Dietary and lifestyle- related factors are
key determinants of the risk of developing
cancer, with certain cancers being more
dependent on dietary habits than others1–9.
Consistent with this notion, obesity is
estimated to account for 14% to 20% of
all cancer- related mortality in the United
States7, leading to guidelines on nutrition
and physical activity for reducing the risk of
developing cancer6. In addition, given the
emerging propensity of cancer cells, but not
of normal tissues, to disobey anti- growth
signals (owing to oncogenic mutations)10
and their inability to properly adapt to
fasting conditions11,12, there is growing
interest in the possibility that certain
calorie- limited diets could also become
an integral part of cancer prevention and,
perhaps, of cancer treatment as a means
to increase efficacy and tolerability of
anticancer agents11–13.
Even though in the past decade we
have witnessed unprecedented changes
and remarkable advances in cancer
treatment14,15, there remains a crucial need
for more effective and, possibly, curative
therapy. In this Opinion article, we discuss
the biological rationale for using fasting
or fasting- mimicking diets (FMDs) to
blunt TEAEs but also to prevent and treat
cancer. We also illustrate the caveats of
this experimental approach18,19 and the
published and ongoing clinical studies in
which fasting or FMDs have been applied to
patients with cancer.
Systemic and cellular fasting response
Fasting leads to changes in the activity of
many metabolic pathways associated with
the switch into a mode able to generate
energy and metabolites using carbon
sources released primarily from adipose
tissue and in part from muscle. The changes
in the levels of circulating hormones and
metabolites translate into a reduction
in cell division and metabolic activity of
normal cells and ultimately protect them
from chemotherapeutic insults11,12. Cancer
cells, by disobeying the anti- growth orders
dictated by these starvation conditions,
can have the opposite response of normal
cells and therefore become sensitized to
chemotherapy and other cancer therapies.
Systemic response to fasting. The
response to fasting is orchestrated in part
by the circulating levels of glucose, insulin,
glucagon, growth hormone (GH), IGF1,
glucocorticoids and adrenaline. During
an initial post- absorptive phase, which
typically lasts 6–24 hours, insulin levels start
to fall, and glucagon levels rise, promoting
the breakdown of liver glycogen stores
(which are exhausted after approximately
24 hours) and the consequent release of
glucose for energy. Glucagon and low levels
of insulin also stimulate the breakdown of
triglycerides (which are mostly stored in
adipose tissue) into glycerol and free fatty
acids. During fasting, most tissues utilize
fatty acids for energy, while the brain relies
on glucose and on ketone bodies produced
by hepatocytes (ketone bodies can be
produced from acetyl- CoA generated from
fatty acid β- oxidation or from ketogenic
amino acids). In the ketogenic phase of
fasting, ketone bodies reach concentrations
in the millimolar range, typically starting
after 2–3 days from the beginning of the
fast. Together with fat- derived glycerol
and amino acids, ketone bodies fuel
approaches for tumours but also, and just
as importantly, for strategies to reduce
the side effects of cancer treatments15,16.
The issue of treatment- emergent adverse
events (TEAEs) is one of the key hurdles in
medical oncology15,16. In fact, many patients
with cancer experience acute and/or long-
term side effects of cancer treatments,
which may require hospitalization and
aggressive treatments (such as antibiotics,
haematopoietic growth factors and blood
transfusions) and profoundly affect their
quality of life (for example, chemotherapy-
induced peripheral neuropathy)16. Thus,
effective toxicity- mitigating strategies are
warranted and anticipated to have major
medical, societal and economic impact15,16.
Fasting forces healthy cells to enter a
slow division and highly protected mode
that protects them against toxic insults
derived from anticancer drugs while
sensitizing different types of cancer cells
to these therapeutics11,12,17. This discovery
implies that a single dietary intervention
could potentially help address different
and equally important aspects of cancer
OPINION
Fasting and cancer: molecular
mechanisms and clinical application
Alessio Nencioni, Irene Caffa, Salvatore Cortellino and Valter D. Longo
Abstract | The vulnerability of cancer cells to nutrient deprivation and their
dependency on specific metabolites are emerging hallmarks of cancer. Fasting or
fasting- mimicking diets (FMDs) lead to wide alterations in growth factors and in
metabolite levels, generating environments that can reduce the capability of
cancer cells to adapt and survive and thus improving the effects of cancer
therapies. In addition, fasting or FMDs increase resistance to chemotherapy in
normal but not cancer cells and promote regeneration in normal tissues, which
could help prevent detrimental and potentially life- threatening side effects of
treatments. While fasting is hardly tolerated by patients, both animal and clinical
studies show that cycles of low- calorie FMDs are feasible and overall safe. Several
clinical trials evaluating the effect of fasting or FMDs on treatment- emergent
adverse events and on efficacy outcomes are ongoing. We propose that the
combination of FMDs with chemotherapy , immunotherapy or other treatments
represents a potentially promising strategy to increase treatment efficacy , prevent
resistance acquisition and reduce side effects.

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gluconeogenesis, which maintains glucose
levels at a concentration of approximately
4 mM (70 mg per dl), which is mostly
utilized by the brain. Glucocorticoids and
adrenaline also contribute to direct the
metabolic adaptations to fasting, helping
maintain blood sugar levels and stimulating
lipolysis20,21. Notably, although fasting can
at least temporarily increase GH levels (to
increase gluconeogenesis and lipolysis and
to decrease peripheral glucose uptake),
fasting reduces IGF1 levels. In addition,
under fasting conditions, IGF1 biological
activity is restrained in part by an increase
in the levels of insulin- like growth factor-
binding protein 1 (IGFBP1), which binds
to circulating IGF1 and prevents its
interaction with the corresponding cell
surface receptor22. Finally, fasting decreases
the levels of circulating leptin, a hormone
predominantly made by adipocytes that
inhibits hunger, while increasing the levels
of adiponectin, which increases fatty acid
breakdown23,24. Thus, in conclusion, the
hallmarks of the mammalian systemic
response to fasting are low levels of glucose
and insulin, high levels of glucagon and
ketone bodies, low levels of IGF1 and leptin
and high levels of adiponectin.
Cellular response to fasting. The response
of healthy cells to fasting is evolutionarily
conserved and confers cell protection, and
at least in model organisms, has been shown
to increase lifespan and healthspan12,22,25–31.
The IGF1 signalling cascade is a key
signalling pathway involved in mediating the
effects of fasting at the cellular level. Under
normal nutrition, protein consumption and
increased levels of amino acids increase
IGF1 levels and stimulate AKT and mTOR
activity, thereby boosting protein synthesis.
Vice versa, during fasting, IGF1 levels and
downstream signalling decrease, reducing
AKT- mediated inhibition of mammalian
FOXO transcription factors and allowing
these transcription factors to transactivate
genes, leading to the activation of enzymes
such as haem oxygenase 1 (HO1),
superoxide dismutase (SOD) and catalase
with antioxidant activities and protective
effects32–34. High glucose levels stimulate
protein kinase A (PKA) signalling, which
negatively regulates the master energy sensor
AMP- activated protein kinase (AMPK)35,
which, in turn, prevents the expression of
the stress resistance transcription factor
early growth response protein 1 (EGR1)
(Msn2 and/or Msn4 in yeast)26,36. Fasting
and the resulting glucose restriction inhibit
PKA activity, increase AMPK activity
and activate EGR1 and thereby achieve
cell-protective effects, including those in
the myocardium22,25,26.
Lastly, fasting and FMDs (see below
for their composition) also have the ability
to promote regenerative effects (Box 1) by
molecular mechanisms, some of which
have been implicated in cancer, such as
increased autophagy or induction of sirtuin
activity22,37–49.
Dietary approaches in cancer
FMDs. The dietary approaches based on
fasting that have been investigated more
extensively in oncology, both preclinically
and clinically, include water fasting
(abstinence from all food and drinks except
for water) and FMDs11,12,17,25,26,50–60 (TaBle 1).
Preliminary clinical data indicate that a
fast of at least 48 hours may be required
to achieve clinically meaningful effects in
oncology, such as preventing chemotherapy-
induced DNA damage to healthy tissues
and helping to maintain patient quality of
life during chemotherapy52,53,61. However,
most patients refuse or have difficulties
completing water fasting, and the
potential risks of the extended calorie and
micronutrient deficiency associated with it
are difficult to justify. FMDs are medically
designed dietary regimes very low in calories
(that is, typically between 300 and 1,100 kcal
per day), sugars and proteins that recreate
many of the effects of water- only fasting
but with better patient compliance and
reduced nutritional risk22,61,62. During an
FMD, patients typically receive unrestricted
amounts of water, small, standardized
portions of vegetable broths, soups,
juices, nut bars, and herbal teas, as well
as supplements of micronutrients.
In a clinical study of 3 monthly cycles of
a 5-day FMD in generally healthy subjects,
the diet was well tolerated and reduced
trunk and total body fat, blood pressure
and IGF1 levels62. In previous and ongoing
oncological clinical trials, fasting or FMDs
have typically been administered every
3–4 weeks, for example, in combination with
chemotherapy regimens, and their duration
has ranged between 1 and 5 days52,53,58,61,63–68.
Importantly, no serious adverse events
(level G3 or above, according to Common
Terminology Criteria for Adverse Events)
were reported in these studies52,53,58,61.
Ketogenic diets. Ketogenic diets (KDs) are
dietary regimens that have normal calorie,
high- fat and low- carbohydrate content69,70.
In a classical KD, the ratio between the
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Box 1 | Regenerative effects of fasting and FMDs
Fasting and fasting- mimicking diets (FmDs) can cause substantial regenerative effects in mouse
models. mice fed an FmD starting at 16 months of age for 4 days twice a month show signs of adult
neurogenesis, as measured by an increase in the proliferation of immature neurons and by the
representation of neural precursors and neural stem cells22. This effect is accompanied by a
reduction in circulating and hippocampal IGF1 and in hippocampal protein kinase A (PKA) activity
and by a twofold increase in the hippocampal expression of the transcription factor neuroD1,
which is important for neuronal protection and differentiation39. An FmD also led to signs of
skeletal muscle rejuvenation in mice — it countered the age- dependent decline in the expression
of PAX7, a transcription factor that promotes myogenesis by regulating skeletal muscle satellite
cell biogenesis and self- renewal22,40. Periodic fasting also promotes haematopoietic stem cell self-
renewal and ameliorates age- dependent myeloid- bias in mice25. IGF1 or PKA deficiency led to
similar effects, highlighting a key role for these two signalling pathways in the pro- regenerative
effects of fasting in the haematopoietic system. Strikingly, periodic FmD cycles can also promote
pancreatic β- cell regeneration, by reducing PKA and mTor activity and by increasing the
expression of developmental markers such as Nanog, Sox17, Sox2, Ngn3 and Ins, followed by
Ngn3-mediated generation of insulin- producing β- cells41.
Fasting or FmDs induce autophagy, a naturally occurring, evolutionarily conserved mechanism
that disassembles unnecessary or dysfunctional cellular components and allows survival by
feeding cell metabolism and repair mechanisms22,42,43. Studies show that autophagy improves
healthspan, promotes longevity in mammals and contributes to the lifespan- prolonging effects of
calorie- limited diets44,45. In healthy cells, autophagy exerts multiple effects that converge to avoid
the risk of malignant transformation, including the preservation of an optimal energetic and redox
metabolism, the disposal of potentially harmful and genotoxic molecules, the fight of infections
linked to cancer and the preservation of healthy stem cell compartments46–48. A periodic FmD
prevented the age- dependent accumulation of p62, a marker of defective autophagy, which
suggests that the healthspan- promoting effects of FmDs are carried out at least in part by
promotion of autophagic activity22.
Finally, sirtuins, which function as nAD+-dependent deacetylases and were ascribed protective
and lifespan- extending effects in model organisms, also become more active during fasting37,38.
The nAD+-producing enzyme nicotinamide phosphoribosyltransferase (nAmPT) and, consequently,
intracellular nAD+ levels are upregulated during nutrient deprivation as well, further promoting the
activity of mitochondrial sirtuins, particularly SIrT3 and SIrT4, and ultimately protecting cells from
genotoxic agents, including chemotherapeutics49.
weight of fat and the combined weight of
carbohydrate and protein is 4:1. Of note,
FMDs are also ketogenic because they have
high- fat content and have the ability to
induce substantial elevations ( ≥0.5 mmol
per litre) in the levels of circulating ketone
bodies. In humans, a KD can also reduce
IGF1 and insulin levels (by more than
20% from baseline values), although
these effects are affected by the levels and
types of carbohydrates and protein in
the diet71. KDs can reduce blood glucose
levels, but they normally remain within
the normal range (that is, >4.4 mmol per
litre)71. Notably, KDs may be effective for
preventing the increase in glucose and
insulin that typically occurs in response to
PI3K inhibitors, which was proposed
to limit their efficacy72. Traditionally, KDs
have been used for treating refractory
epilepsy, mainly in children69. In mouse
models, KDs induce anticancer effects,
particularly in glioblastoma70,72–86. Clinical
studies indicate that KDs probably have no
substantial therapeutic activity when used
as single agents in patients with cancer
and suggest that potential benefits of these
diets should be sought in combination with
other approaches, such as chemotherapy,
radiotherapy, antiangiogenic treatments,
PI3K inhibitors and FMDs72,73. KDs
were reported to have neuroprotective
effects in peripheral nerves and in the
hippocampus87,88. However, it remains to
be established whether KDs also have pro-
regenerative effects similar to fasting or
FMDs (Box 1) and whether KDs also can
be used to protect living mammals from
the toxicity of chemotherapy. Notably, the
regenerative effects of fasting or FMDs
appear to be maximized by the switch
from the starvation- response mode,
which involves the breakdown of cellular
components and the death of many cells,
and the re- feeding period, in which cells and
tissues undergo reconstruction22. Because
KDs do not force entry into a starvation
mode, do not promote a major breakdown
of intracellular components and tissues
and do not include a refeeding period,
they are unlikely to cause the type of
coordinated regeneration observed during
the FMD refeeding.
Calorie restriction. While chronic calorie
restriction (CR) and diets deficient in
specific amino acids are very different from
periodic fasting, they share with fasting and
FMDs a more or less selective restriction
in nutrients, and they have anticancer
effects81,89–112. CR typically involves a chronic
20–30% reduction in energy intake from the
standard calorie intake that would allow an
individual to maintain a normal weight113,114.
It is very effective in reducing cardiovascular
risk factors and cancer incidence in model
organisms, including primates108,109,114.
However, CR can cause side effects, such as
changes in physical appearance, increased
cold sensitivity, reduced strength, menstrual
irregularities, infertility, loss of libido,
osteoporosis, slower wound healing, food
obsession, irritability and depression. In
patients with cancer, there are substantial
concerns that it may exacerbate malnutrition
and that it will unavoidably cause excessive
loss of lean body mass18,113–116. CR reduces
fasting blood glucose levels, though they
remain within the normal range114. In
humans, chronic CR does not affect IGF1
levels unless a moderate protein restriction
is also implemented117. Studies show that
by reducing mTORC1 signalling in Paneth
cells, CR augments their stem cell function
and that it also protects reserve intestinal
stem cells from DNA damage118,119, but it is
unknown whether pro- regenerative effects
in other organs are also elicited by CR. Thus,
the available data suggest that fasting and
FMDs create a metabolic, regenerative
and protective profile that is distinct and
probably more potent than that elicited by a
KD or CR.
Fasting and FMDs in therapy
Effects on hormone and metabolite
levels. Many of the changes in the levels of
circulating hormones and metabolites that
are typically observed in response to fasting
have the capability to exert antitumour
effects (that is, reduced levels of glucose,
IGF1, insulin and leptin and increased
levels of adiponectin)23,120,121 and/or to afford
protection of healthy tissues from side effects
(that is, reduced levels of IGF1 and glucose).
Because ketone bodies can inhibit histone
deacetylases (HDACs), the fasting- induced
increase of ketone bodies may help slow
tumour growth and promote differentiation
through epigenetic mechanisms122. However,
the ketone body acetoacetate has been
shown to accelerate, instead of reduce,
the growth of certain tumours, such as
melanomas with mutated BRAF123. Those
changes for which there is the strongest
evidence for a role in the beneficial effects
of fasting and FMDs against cancer are the

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Table 1 | Dietary approaches with proposed applications in oncology
Type of
diet
Restriction
in calories
Composition
Schedule
IGF1
reduction
(humans)
Glucose
reduction
(humans)
Ketone
bodies
increase
(humans)
Location of
pro-regenerative
effects
Protection from
chemotherapy
toxicity
Fasting or
FMD
>50%
Vegan and
low-protein
and low-sugar,
high-plant-based
fat composition,
with micronutrient
supplementation
Typically 2–5
consecutive
days per
month
Yes
Yes
Yes
Haematopoietic
system, central
nervous system,
skeletal muscle and
pancreatic β- cells
(mouse data)22,25,41,153
Yes (mouse data
and DNA damage
analyses in patient
leukocytes)12,25,26,29,51–53
Calorie
restriction
20–40%
Reduction in all
diet constituents
except for
vitamins and
minerals
Chronic
Only in the
presence
of protein
restriction117
No
No
Intestinal niche
stem cells (mouse
data)118,119
Yes (effect lower than
that with fasting or
FMDs; mouse data)51
Ketogenic
diet
None
(isocaloric)
High-fat, low-
carbohydrate
composition, with
adequate protein
content
Chronic
Yes
No
Yes
Peripheral nerves
(rat data)87
NA
FMD, fasting- mimicking diet; NA , not available.
reductions in the levels of IGF1 and glucose.
At the molecular level, fasting or an FMD
reduces intracellular signalling cascades
including IGF1R–AKT–mTOR–S6K and
cAMP–PKA signalling, increases autophagy,
helps normal cells withstand stress and
promotes anticancer immunity25,29,56,124.
Differential stress resistance: increasing
chemotherapy tolerability. Some yeast
oncogene orthologues, such as Ras
and Sch9 (functional orthologue of
mammalian S6K), are able to decrease stress
resistance in model organisms27,28.
In addition, mutations that activate IGF1R,
RAS, PI3KCA or AKT, or that inactivate
PTEN, are present in the majority of
human cancers10. Together, this led to the
hypothesis that starvation would cause
opposite effects in cancer versus normal
cells in terms of their ability to withstand
cell stressors, including chemotherapeutics.
In other words, starvation can lead to a
differential stress resistance (DSR) between
normal and cancer cells. According to the
DSR hypothesis, normal cells respond to
starvation by downregulating proliferation-
associated and ribosome biogenesis and/or
assembly genes, which forces cells to enter
a self- maintenance mode and shields them
from the damage caused by chemotherapy,
radiotherapy and other toxic agents.
By contrast, in cancer cells, this self-
maintenance mode is prevented through
oncogenic changes, which cause constitutive
inhibition of stress response pathways12
(Fig. 1). Consistent with the DSR model,
short- term starvation or the deletion of
proto- oncogene homologues (that is, Sch9
or both Sch9 and Ras2) increased protection
of Saccharomyces cerevisiae against oxidative
stress or chemotherapy drugs by up to
100-fold as compared with yeast cells
expressing the constitutively active oncogene
homologue Ras2val19. Similar results were
obtained in mammalian cells: exposure to
low- glucose media protected primary mouse
glia cells against toxicity from hydrogen
peroxide or cyclophosphamide (a pro-
oxidant chemotherapeutic) but did not
protect mouse, rat and human glioma and
neuroblastoma cancer cell lines. Consistent
with these observations, a 2-day fasting
effectively increased the survival of mice
treated with high- dose etoposide compared
with non- fasted mice and increased the
survival of neuroblastoma allograft-
bearing mice compared with non- fasted
tumour-bearing mice12.
Subsequent studies found that reduced
IGF1 signalling in response to fasting
protects primary glia and neurons, but
not glioma and neuroblastoma cells, from
cyclophosphamide and from pro- oxidative
compounds and protects mouse embryonic
fibroblasts from doxorubicin29. Liver
IGF1-deficient (LID) mice, transgenic
animals with a conditional liver Igf1 gene
deletion that exhibit a 70–80% reduction
in circulating IGF1 levels (levels similar
to those achieved by a 72-hour fast in
mice)29,125, were protected against three out
of four chemotherapy drugs tested, including
doxorubicin. Histology studies showed signs
of doxorubicin- induced cardiac myopathy
in only doxorubicin- treated control mice
but not in LID mice. In experiments
with melanoma- bearing animals treated with
doxorubicin, no difference in terms of
disease progression between control and
LID mice was observed, indicating that
cancer cells were not protected from
chemotherapy by reduced IGF1 levels.
Yet, again, tumour- bearing LID mice
exhibited a remarkable survival advantage
compared with the control animals owing
to their ability to withstand doxorubicin
toxicity29. Thus, overall, these results
confirmed that IGF1 downregulation is a
key mechanism by which fasting increases
chemotherapy tolerability.
Both dexamethasone and mTOR
inhibitors are widely used in cancer
treatment, either because of their efficacy
as anti- emetics and anti- allergics (that is,
corticosteroids) or for their antitumour
properties (that is, corticosteroids and
mTOR inhibitors). However, one of their
main and frequently dose- limiting side
effects is hyperglycaemia. Consistent with
the notion that increased glucose–cAMP–
PKA signalling reduces resistance to
toxicity of chemotherapeutic drugs12,26,126,
both dexamethasone and rapamycin
increase toxicity of doxorubicin in mouse
cardiomyocytes and mice26. Interestingly
it was possible to reverse such toxicity by
reducing circulating glucose levels through
either fasting or insulin injections26. These
interventions reduce PKA activity while
increasing AMPK activity and thereby
activating EGR1, indicating that cAMP–
PKA signalling mediates the fasting- induced
DSR via EGR1 (reF.26). EGR1 also promotes
the expression of cardioprotective peptides,
such as the atrial natriuretic peptide (ANP)
and the B- type natriuretic peptide (BNP)
in heart tissue, which contributes to the
resistance to doxorubicin. Furthermore,
fasting and/or FMD might protect mice
from doxorubicin- induced cardiomyopathy
by boosting autophagy, which may promote
cellular health by reducing reactive oxygen
species (ROS) production through the
elimination of dysfunctional mitochondria
and by removal of toxic aggregates.
In addition to reducing chemotherapy-
induced toxicity in cells and increasing
survival of chemotherapy-treated
mice, cycles of fasting induce bone
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Basal membrane
Healthy cell
Cancer cell
Chemotherapy
Chemotherapy combined
with fasting or an FMD
Dead cell
Fig. 1 | Differential stress resistance versus differential stress sensitization. Chemotherapy acts
on both cancer cells and normal cells, inducing tumour shrinkage but almost inevitably also causing
side effects that can be severe or even life threatening because of the damage to many epithelial and
non- epithelial tissues. On the basis of the available preclinical data, fasting or a fasting-mimicking diet
(FMD) could prove useful to separate the effects of chemotherapy , and possibly of newer cancer drugs,
on normal versus cancer cells. Owing to the presence of oncogenic mutations that constitutively
activate growth- promoting signalling cascades, cancer cells fail to properly adapt to starvation con-
ditions. As a result, many types of cancer cells, but not normal cells, experience functional imbalances,
becoming sensitized to toxic agents, including chemotherapy (differential stress sensitization).
Conversely , fasting or an FMD initiates an evolutionarily conserved molecular response that makes
normal cells but not cancer cells more resistant to stressors, including chemotherapy (differential
stress resistance). The predicted clinical translation of these differential effects of fasting or FMDs on
normal versus cancer cells is a reduction in the side effects of cancer treatments, on the one hand, and
improved tumour responses, patient progression- free survival and overall survival, on the other.
marrow regeneration and prevent the
immunosuppression caused by cyclo-
phosphamide in a PKA- related and
IGF1-related manner25. Thus, compelling
preclinical results indicate the potential of
fasting and FMDs to increase chemotherapy
tolerability and to avoid major side effects.
Because initial clinical data lend further
support to this potential, these preclinical
studies build a strong rationale for evaluating
FMDs in randomized clinical trials with
TEAEs as a primary end point.
Differential stress sensitization: increasing
the death of cancer cells. If used alone,
most dietary interventions, including
fasting and FMDs, have limited effects
against cancer progression. According to
the differential stress sensitization (DSS)
hypothesis, the combination of fasting or
FMDs with a second treatment is much
more promising11,12. This hypothesis
predicts that, while cancer cells are able
to adapt to limited oxygen and nutrient
concentrations, many types of cancer cells
are not able to execute changes that would
allow survival in the nutrient- deficient
and toxic environment generated by the
combination of fasting and chemotherapy,
for example. Early experiments in breast
cancer, melanoma and glioma cells found
a paradoxical increase in the expression
of proliferation- associated genes or of
ribosome biogenesis and assembly genes
in response to fasting11,12. Such changes
were accompanied by unexpected AKT and
S6K activation, a propensity to generate
ROS and DNA damage and a sensitization
to DNA- damaging drugs (via DSS)11. We
consider such an inappropriate response
of cancer cells to the altered conditions
including the reduction in IGF1 and glucose
levels caused by fasting or FMDs as a key
mechanism underlying the antitumour
properties of these dietary interventions
and their potential usefulness for separating
the effects of anticancer treatments on
normal versus malignant cells11,12 (Fig. 1).
In line with the DSS hypothesis, periodic
cycles of fasting or of FMDs are sufficient
to slow the growth of many types of
tumour cells, ranging from solid tumour
cell lines to lymphoid leukaemia cells,
in the mouse and, most importantly, to
sensitize cancer cells to chemotherapeutics,
radiotherapy and tyrosine kinase inhibitors
(TKIs)11,17,22,25,50,54–57,59,60,124,127,128.
By reducing glucose availability and
increasing fatty acid β- oxidation, fasting
or FMDs can also promote a switch from
aerobic glycolysis (Warburg effect) to
mitochondrial oxidative phosphorylation
in cancer cells, which is necessary for
sustaining cancer cell growth in the most
nutrient- poor environment50 (Fig. 2). This
switch leads to increased ROS production11
as a result of increased mitochondrial
respiratory activity and may also involve
a reduction in cellular redox potential
owing to decreased glutathione synthesis
from glycolysis and the pentose phosphate
pathway50. The combined effect of ROS
augmentation and reduced antioxidant
protection boosts oxidative stress in
cancer cells and amplifies the activity of
chemotherapeutics. Notably, because a
high glycolytic activity demonstrated by
high- lactate production is predictive of
aggressiveness and metastatic propensity in
several types of cancer129, the anti- Warburg
effects of fasting or FMD have the potential

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Cancer cell
M2 macrophages
Immunosuppression
Adenosine
Fasting or an FMD
Autophagy
CD73
Insulin
IGF1
IGF1R
HO1
↑ ROS
Regulatory
T cells
Cytotoxic
T lymphocytes
Chemotherapy
Nucleus
Aerobic
glycolysis
GLUT
Glucose
Glucose
Insulin receptor
DNA
damage
p53
Cell death
Mitochondrion
↑ OxPhos
Fig. 2 | Mechanisms of fasting or FMD- dependent killing of cancer cells
in solid tumours. Preclinical and initial clinical data indicate that fasting or
fasting- mimicking diets (FMDs) reduce the levels of tumour growth-
promoting nutrients and factors, including glucose, IGF1 and insulin. Fasting
can cause an anti- Warburg effect by reducing glucose uptake via glucose
transporters (GLUTs) and aerobic glycolysis and forcing cancer cells to
increase oxidative phosphorylation (OxPhos); this increases the production
of reactive oxygen species (ROS) in cancer cells and, resultantly , oxidative
DNA damage, p53 activation, DNA damage and cell death, particularly in
response to chemotherapy. By activating autophagy , fasting can reduce
CD73 levels in some cancer cells, thereby blunting adenosine production in
the extracellular environment and preventing the shift of macrophages
towards an immunosuppressive M2 phenotype. Finally , fasting or FMDs can
downregulate haem oxygenase 1 (HO1) expression in breast cancer cells,
which makes them more susceptible to CD8+ cytotoxic T cells, possibly by
countering the immunosuppressive effect of regulatory T (Treg) cells. Notably ,
fasting or an FMD can have very different and even opposite effects in
different cancer cell types or even within the same cancer cell type.
to be particularly effective against aggressive
and metastatic cancers.
Apart from a change in metabolism,
fasting or FMDs elicit other changes that
can promote DSS in pancreatic cancer
cells. Fasting increases the expression levels
of equilibrative nucleoside transporter 1
(ENT1), the transporter of gemcitabine
across the plasma membrane, leading
to improved activity of this drug128.
In breast cancer cells, fasting causes
SUMO2-mediated and/or SUMO3-mediated
modification of REV1, a DNA polymerase
and a p53-binding protein127. This
modification reduces the ability of REV1
to inhibit p53, leading to increased
p53-mediated transcription of pro- apoptotic
genes and, ultimately, to cancer cell demise
(Fig. 2). Fasting also increases the ability of
commonly administered TKIs to stop cancer
cell growth and/or death by strengthening
MAPK signalling inhibition and, thereby,
blocking E2F transcription factor- dependent
gene expression but also by reducing glucose
uptake17,54. Finally, fasting can upregulate
the leptin receptor and its downstream
signalling through the protein PR/SET
domain 1 (PRDM1) and thereby inhibit
the initiation and reverse the progression
of B cell and T cell acute lymphoblastic
leukaemia (ALL), but not of acute myeloid
leukaemia (AML)55. Interestingly, an
independent study demonstrated that
B cell precursors exhibit a state of chronic
restriction in glucose and energy supplies
imposed by the transcription factors PAX5
and IKZF1 (reF.130). Mutations in the genes
encoding these two proteins, which are
present in more than 80% of the cases of
pre- B cell ALL, were shown to increase
glucose uptake and ATP levels. However,
reconstituting PAX5 and IKZF1 in pre-
B-ALL cells led to an energy crisis and cell
demise. Taken together with the previous
study, this work indicates that ALL may
be sensitive to the nutrient and energy
restriction imposed by fasting, possibly
representing a good clinical candidate for
testing the efficacy of fasting or FMD.
Notably, it is likely that many cancer
cell types, including AML29, can acquire
resistance by circumventing the metabolic
changes imposed by fasting or FMDs, a
possibility that is further increased by the
metabolic heterogeneity that characterizes
many cancers129. Thus, a major goal for the
near future will be to identify the types of
cancer that are most susceptible to these
dietary regimens by means of biomarkers.
On the other hand, when combined with
standard therapies, fasting or FMDs have
rarely resulted in the acquisition of resistance
in cancer mouse models, and resistance to
fasting combined with chemotherapy is also
uncommon in studies in vitro, underlining
the importance of identifying therapies
that, when combined with FMDs, result
in potent toxic effects against cancer cells
with minimal toxicity to normal cells and
tissues11,17,50,55–57,59,124.
Antitumour immunity enhancement
by fasting or FMDs. Recent data suggest
that fasting or FMDs by themselves, and
to a greater extent when combined with
chemotherapy, trigger the expansion
of lymphoid progenitors and promote
tumour immune attack via different
mechanisms25,56,60,124. An FMD reduced
the expression of HO1, a protein that
confers protection against oxidative
damage and apoptosis, in cancer cells
in vivo but upregulated HO1 expression in
normal cells124,131. HO1 downregulation
in cancer cells mediates FMD- induced
chemosensitization by increasing CD8+
tumour- infiltrating lymphocyte- dependent
cytotoxicity, which may be facilitated by
the downregulation of regulatory T cells124
(Fig. 2). Another study, which confirmed the
ability of fasting or FMDs and CR mimetics
to improve anticancer immunosurveillance,
implies that the anticancer effects of
fasting or FMDs may apply to autophagy-
competent, but not autophagy- deficient,
cancers56. Finally, a recent study of
alternate- day fasting for 2 weeks in a
mouse colon cancer model showed that,
by activating autophagy in cancer cells,
fasting downregulates CD73 expression and
consequently decreases the production of
immunosuppressive adenosine by cancer
cells60. Ultimately, CD73 downregulation via
fasting was shown to prevent macrophage
shift to an M2 immunosuppressive
phenotype (Fig. 2). On the basis of these
studies, it is appealing to speculate that
FMDs could be particularly useful instead
of or in combination with immune
checkpoint inhibitors132, cancer vaccines
or other drugs that prompt antitumour
immunity, including some conventional
chemotherapeutics133.
Anticancer diets in mouse models
Overall, the results of preclinical studies
of fasting or FMDs in animal cancer
models, including models for metastatic
cancer (TaBle 2), show that periodic fasting
or FMDs achieve pleiotropic anticancer
effects and potentiate the activity of
chemotherapeutics and TKIs while exerting
protective and regenerative effects in
multiple organs22,25. Achieving the same
effects without fasting and/or FMDs would
require first the identification and then
the use of multiple effective, expensive and
frequently toxic drugs and would probably
be without the advantage of inducing
healthy cell protection. It is noteworthy
that in at least two studies fasting combined
with chemotherapy proved to be the only
intervention capable of achieving either
complete tumour regressions or long- term
survival in a consistent fraction of the
treated animals11,59.
Chronic KDs also show a tumour
growth- delaying effect when used as
a monotherapy, particularly in brain cancer
mouse models77,78,80–82,84,134. Gliomas in mice
maintained on a chronic KD have reduced
expression of the hypoxia marker carbonic
anhydrase 9 and of hypoxia- inducible factor
1α, decreased nuclear factor- κB activation
and reduced vascular marker expression
(that is, vascular endothelial growth factor
receptor 2, matrix metalloproteinase 2 and
vimentin)86. In an intracranial mouse model
of glioma, mice fed a KD exhibited increased
tumour- reactive innate and adaptive
immune responses that were primarily
mediated by CD8+ T cells79. KDs were shown
to improve the activity of carboplatin,
cyclophosphamide and radiotherapy in
glioma, lung cancer and neuroblastoma
mouse models73–75,135. In addition, a recent
study shows that a KD could be very useful
in combination with PI3K inhibitors72. By
blocking insulin signalling, these agents
promote glycogen breakdown in the
liver and prevent glucose uptake in the
skeletal muscle, which leads to transient
hyperglycaemia and to a compensatory
insulin release from the pancreas (a
phenomenon known as ‘insulin feedback’).
In turn, this raise in insulin levels, which can
be protracted, particularly in patients with
insulin resistance, reactivates PI3K–mTOR
signalling in tumours, thus strongly limiting
the benefit of PI3K inhibitors. A KD was
shown to be very effective at preventing
insulin feedback in response to these drugs
and to strongly improve their anticancer
activity in the mouse. Finally, according to a
study in a murine tumour- induced cachexia
model (MAC16 tumours), KDs could help
prevent the loss of fat and non- fat body mass
in patients with cancer85.
CR reduced tumorigenesis in genetic
mouse cancer models, mouse models with
spontaneous tumorigenesis and carcinogen-
induced cancer mouse models, as well as
in monkeys91,92,97,98,101,102,104–106,108,109,136–138.
By contrast, a study found that CR
from middle age actually increases the
incidence of plasma cell neoplasms in
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Table 2 | Fasting or FMDs in cancer mouse models
Cancer model
Mouse strains
Dietary regimen
Main findings
Refs
Metastatic neuroblastoma model
(intravenous cancer cell injection):
NXS2 (mouse neuroblastoma
allograft)
A/J, CD-1 and
athymic nude mice
48 h fasting (water only) given
once prior to high- dose etoposide
injection versus ad libitum diet
Fasting cycles reduced toxicity of
high- dose etoposide in mice but did
not reduce etoposide activity profile
against neuroblastoma allografts
12
Subcutaneous tumour models: 4T1
(mouse breast cancer allograft),
B16 (mouse melanoma allograft),
GL26 (mouse glioma allograft),
ACN (human neuroblastoma
xenograft), MDA- MB-231 (human
breast cancer xenograft) and
OVCAR3 (human ovarian cancer
xenograft).
Metastatic cancer models
(intravenous cancer cell injection):
4T1 (allograft), B16 (allograft),
NXS2 (mouse neuroblastoma
allograft) and Neuro-2a (mouse
neuroblastoma allograft)
BALB/c, C57Bl/6 and
athymic nude mice
48 h fasting (water only) given once
a week between 1 and 4 times, 24 h
prior to and 24 h after chemotherapy
injection versus ad libitum diet
Fasting cycles combined with
doxorubicin or cyclophosphamide
were superior to each treatment
alone in retarding the growth of
subcutaneously growing tumours
and extending survival in metastatic
models of breast cancer, melanoma
and neuroblastoma
11
Subcutaneous tumour models:
ZL55 (human mesothelioma
xenograft) and A549 (human lung
cancer xenograft)
Nude mice
48 h fasting (water only) given once
a week for 3 times, 32 h prior to and
16 h after cisplatin injection versus
ad libitum diet
Fasting sensitized human
mesothelioma and lung cancer
xenografts to cisplatin. Complete
remissions were observed in only the
combination treatments (in 40–60% of
the mice)
59
Subcutaneous tumour models:
H2133 (human lung cancer
xenograft) and HCT116 (human
colorectal cancer xenograft)
Athymic nude mice
48 h fasting (water only) given
once a week for 3 times during
daily treatment with crizotinib or
regorafenib versus ad libitum diet
Fasting improved the clinical activity
of crizotinib and of regorafenib and
boosted their ability to block MAPK
signalling
17
Subcutaneous tumour model: CT26
(mouse colon cancer allograft)
BALB/c mice
48 h fasting (water only) given once
a week for 2 times, 24 h prior to and
24 h after oxaliplatin injection versus
ad libitum diet
Fasting potentiated the anticancer
effects of oxaliplatin, exerted anti-
Warburg effects and promoted
oxidative stress and apoptosis in
cancer cells
50
Subcutaneous tumour models: 4T1
(mouse breast cancer allograft),
B16 (mouse melanoma allograft)
and MCF7 (human breast cancer
xenograft)
BALB/c, C57Bl/6 and
athymic nude mice
48–60 h fasting (water only) or a 96 h
FMD given once a week for 2 to 4
times versus ad libitum diet. Animals
were injected with chemotherapy at
the end of each fasting and/or
FMD cycle
An FMD was as effective as fasting
at reducing tumour progression
when combined with doxorubicin
or cyclophosphamide. The FMD
downregulated HO1 expression in
cancer cells, expanded lymphoid
progenitors in the bone marrow and
boosted anticancer immunity
124
Subcutaneous tumour model:
MCA205 (mouse fibrosarcoma
allograft)
C57Bl/6 and athymic
nude mice
48 h fasting (water only) given once
versus ad libitum diet. Animals
were injected with mitoxantrone or
oxaliplatin at the end of fasting
Fasting and calorie restriction mimetics
improved the efficacy of chemotherapy
in an immune system- dependent
and autophagy- dependent fashion.
Autophagy was shown to allow for
optimal release of ATP from dying
cancer cells, leading to the depletion
of intratumoural regulatory T cells
and thereby improving the anticancer
immune response
56
B- ALL , T- ALL and AML models: Lin−
bone marrow cells were infected
with retroviruses expressing
MYC–IRES–GFP (B- ALL), NOTCH1–
IRES–GFP (T- ALL) or MLL–AF9–
IRES–YFP (AML) and subsequently
transplanted into irradiated mice
C57Bl/6 mice
1 day of fasting followed by 1 day of
feeding, for a total of 6 cycles starting
from day 2 after transplantation
versus ad libitum diet
Fasting inhibited B- ALL and T- ALL
development by upregulation of the
leptin receptor and its downstream
signalling. AML growth was not
affected
55
Subcutaneous tumour model: CT26
(mouse colon cancer allograft)
BALB/c mice
24 h fasting on alternate days for
2 weeks
Fasting inhibited colon cancer growth
and decreased the production of
extracellular adenosine by cancer cells
by supressing CD73 expression
60
Subcutaneous tumour model:
BxPC-3 (human pancreatic cancer
xenograft)
Nu/Nu nude mice
24 h fasting (water only) before the
administration of gemcitabine
Fasting before gemcitabine injection
delayed pancreatic cancer progression
and increased tumour ENT1 levels
128
C57Bl/6 mice139. However, in the same
study, CR also extended maximum
lifespan by approximately 15%, and the
observed increase in cancer incidence
was attributed to the increased longevity
of mice undergoing CR, the age at which
tumour- bearing mice undergoing CR died
and the percentage of tumour- bearing
mice undergoing CR that died. Thus,
the authors concluded that CR probably
retards promotion and/or progression of
existing lymphoid cancers. A meta- analysis
comparing chronic CR with intermittent
CR in terms of their ability to prevent cancer
in rodents concluded that intermittent CR
is more effective in genetically engineered
mouse models, but it is less effective in
chemically induced rat models90. CR was
shown to slow tumour growth and/or to
extend mouse survival in various cancer
mouse models, including ovarian and
pancreatic cancer140,94 and neuroblastoma81.
Importantly, CR improved the activity
of anticancer treatment in several cancer
models, including the activity of an anti-
IGF1R antibody (ganitumab) against
prostate cancer141, cyclophosphamide against
neuroblastoma cells135 and autophagy
inhibition in xenografts of HRAS- G12V-
transformed immortal baby mouse kidney
epithelial cells100. However, CR or a KD in
combination with anticancer therapies seems
to be less effective than fasting. A mouse
study found that, in contrast to fasting
alone, CR alone was not able to reduce the
growth of subcutaneously growing GL26
mouse gliomas and that, again, in contrast
to short- term fasting, CR did not increase
cisplatin activity against subcutaneous 4T1
breast tumours51. In the same study, fasting
also proved substantially more effective than
CR and a KD at increasing the tolerability of
doxorubicin51. Although fasting or an FMD,
CR and a KD likely act on and modulate
overlapping signalling pathways, fasting or
an FMD probably affects such mechanisms
in a more drastic fashion during an intense
acute phase of a maximum duration of
a few days. The phase of refeeding could
then favour the recovery of homeostasis of
the whole organism but also activate and
invigorate mechanisms that can promote
the recognition and removal of the tumour
and regenerate the healthy cells. CR and a
KD are chronic interventions that are able
to only moderately repress nutrient- sensing
pathway, possibly without reaching certain
thresholds necessary to improve the effects
of anticancer drugs, while imposing a major
burden and often a progressive weight loss.
CR and a KD as chronic dietary regimens
in patients with cancer are difficult to
implement and likely bear health risks.
CR would likely lead to severe loss of lean
body mass and the reduction of steroid
hormones and possibly immune function142.
Chronic KDs are also associated with similar
although less severe side effects143. Thus,
periodic fasting and FMD cycles lasting less
than 5 days applied together with standard
therapies have a high potential to improve
cancer treatment while reducing its side
effects. Notably, it will be important to study
the effect of the combination of periodic
FMDs, chronic KDs and standard therapies,
particularly for the treatment of aggressive
cancers such as glioma.
Fasting and FMDs in cancer prevention
Epidemiological studies and studies in
animals, including monkeys108,109,144, and
humans lend support to the notion that
chronic CR and periodic fasting and/or
an FMD could have cancer- preventive
effects in humans. Nevertheless, CR can
hardly be implemented in the general
population owing to issues of compliance
and to possible side effects115. Thus, while
evidence- based recommendations of foods
to prefer (or to avoid) as well as lifestyle
recommendations to reduce cancer risk are
becoming established6,8,9,15, the goal now
is to identify and, possibly, standardize
well tolerated, periodic dietary regimens
with low or no side effects and evaluate
their cancer- preventive efficacy in clinical
studies. As discussed earlier, FMD cycles
cause downregulation of IGF1 and glucose
and upregulation of IGFBP1 and ketone
bodies, which are changes similar to those
caused by fasting itself and are biomarkers of
the fasting response22. When C57Bl/6 mice
(which spontaneously develop tumours,
primarily lymphomas, as they age) were
fed such an FMD for 4 days twice a month
starting at middle age and an ad libitum
diet in the period between FMD cycles, the
incidence of neoplasms was reduced from
approximately 70% in mice on the control
diet to approximately 40% in mice in the
FMD group (an overall 43% reduction)22.
In addition, the FMD postponed by over
3 months the occurrence of neoplasm-
related deaths, and the number of animals
with multiple abnormal lesions was
more than threefold higher in the control
group than in the FMD mice, indicating that
many tumours in the FMD mice were less
aggressive or benign. A previous study of
alternate- day fasting, which was performed
in middle- aged mice for a total of 4 months,
also found that fasting reduced the incidence
of lymphoma, bringing it from 33% (for
control mice) to 0% (in fasted animals)145,
although because of the short duration of
the study it is unknown whether this fasting
regimen prevented or simply delayed the
tumour onset. Furthermore, alternate-day
fasting imposes 15 days per month of
complete water- only fasting, whereas in
the FMD experiment described above mice
were placed on a diet that provided a limited
amount of food for only 8 days per month.
In humans, 3 cycles of a 5-day FMD once
a month were shown to reduce abdominal
obesity and markers of inflammation as
well as IGF1 and glucose levels in subjects
with elevated levels of these markers62,
indicating that periodic use of an FMD
could potentially have preventive effects for
obesity- related or inflammation- related, but
also other, cancers in humans, as it has been
shown for mice22. Therefore, the promising
results of preclinical studies combined with
the clinical data on the effect of an FMD on
risk factors for ageing- associated diseases,
including cancer62, lend support to future
Table 2 (cont.) | Fasting or FMDs in cancer mouse models
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Cancer model
Mouse strains
Dietary regimen
Main findings
Refs
p53+/− mice; these mice are prone
to spontaneous neoplasms (most
commonly sarcoma and lymphoma)
C57Bl/6 mice
24 h fasting (water only) once a week
Fasting delayed the onset of tumours in
adult mice and lowered leptin and IGF1
compared with mice fed ad libitum
89
Age- associated lymphoma
OF-1 mice
Alternate- day fasting initiated at 8
months of age through a 4-month
period
Fasting reduced the incidence
of lymphoma (0% versus 33% for
controls), decreased the mitochondrial
generation of ROS and increased
spleen mitochondrial SOD activity
145
B- ALL , B cell acute lymphoblastic leukaemia; ENT1, equilibrative nucleoside transporter 1; FMD, fasting- mimicking diet; GFP, green fluorescent protein; HO1, haem
oxygenase 1; ROS, reactive oxygen species; SOD, superoxide dismutase; T- ALL , T cell acute lymphoblastic leukaemia; YFP, yellow fluorescent protein.
randomized studies of FMDs as a possibly
effective tool to prevent cancer, as well as
other ageing-associated chronic conditions,
in humans.
Clinical applicability in oncology
Four feasibility studies of fasting and FMDs
in patients undergoing chemotherapy
have been published as of today52,53,58,61.
In a case series of 10 patients diagnosed
with various types of cancer, including
breast, prostate, ovarian, uterus, lung
and oesophageal cancer, who voluntarily
fasted for up to 140 hours before and/or up
to 56 hours following chemotherapy, no
major side effects caused by fasting itself
other than hunger and lightheadedness
were reported58. Those patients (six) who
underwent chemotherapy with and without
fasting reported a significant reduction
in fatigue, weakness and gastrointestinal
adverse events while fasting. In addition, in
those patients in which cancer progression
could be assessed, fasting did not prevent
chemotherapy- induced reductions in
tumour volume or in tumour markers.
In another study, 13 women with HER2
(also known as ERBB2) negative, stage II/III
breast cancer receiving neo- adjuvant
taxotere, adriamycin and cyclophosphamide
(TAC) chemotherapy were randomized to
fast (water only) 24 hours before and after
beginning chemotherapy or to nutrition
according to standard guidelines52.
Short- term fasting was well tolerated and
reduced the drop in mean erythrocyte
and thrombocyte counts 7 days after
chemotherapy. Interestingly, in this study,
the levels of γ- H2AX (a marker of DNA
damage) were increased 30 minutes after
chemotherapy in leukocytes from non- fasted
patients but not in patients who had fasted.
In a dose escalation of fasting in patients
undergoing platinum- based chemotherapy,
20 patients (who were primarily treated
for either urothelial, ovarian or breast
cancer) were randomized to fast for
24, 48 or 72 hours (divided as 48 hours
before chemotherapy and 24 hours after
chemotherapy)53. Feasibility criteria (defined
as three or more out of six subjects in each
cohort consuming ≤200 kcal per day during
the fast period without excess toxicity)
were met. Fasting- related toxicities were
always grade 2 or below, the most common
being fatigue, headache and dizziness. As in
the previous study, reduced DNA damage
(as detected by comet assay) in leukocytes
from subjects who fasted for at least 48 hours
(as compared with subjects who fasted for
only 24 hours) could also be detected in this
small trial. In addition, a nonsignificant
trend towards less grade 3 or grade 4
neutropenia in patients who fasted for
48 and 72 hours versus those who fasted
for only 24 hours was also documented.
Very recently, a randomized crossover
clinical trial was conducted assessing the
effects of an FMD on quality of life and
side effects of chemotherapy in a total of
34 patients with breast or ovarian cancer61.
The FMD consisted of a daily caloric intake
of <400 kcal, primarily by juices and broths,
starting 36–48 hours before the beginning
of chemotherapy and lasting until 24 hours
after the end of chemotherapy. In this study,
the FMD prevented the chemotherapy-
induced reduction in quality of life and
it also reduced fatigue. Again, no serious
adverse events of the FMD were reported.
Several other clinical trials of FMDs in
combination with chemotherapy or with
other types of active treatments are currently
ongoing at US and European hospitals,

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a
b
Treatment
schedule
Dose reductions
Metabolic or
genetic rewiring
Change of therapy
Relapse
Treatment
schedule
Reduced metabolic
or genetic rewiring
Relapse-free
survival
Treatment
dose
Sensitive cancer
cell clones
Resistant cancer
cell clones
G3 and/or
G4 TEAE
G1 and/or
G2 TEAE
Cycle of
fasting or FMD
Cancer-free survival
Dead
cancer cell
Fig. 3 | Working hypothesis for the effects of the combination of fasting and/or FMDs with standard therapy in oncology. a | The benefit of cancer
treatments is limited by the development of resistance to the agents that are employed but also by treatment- emergent adverse events (TEAEs), which
can be severe or even life threatening and may require hospitalization (G3 and/or G4 TEAEs according to Common Terminology Criteria for Adverse Events).
Disease progression under treatment and G3 and/or G4 TEAEs are the main causes of treatment discontinuations and of the switch to other lines of treat-
ment or to palliative care. b | Fasting- mimicking diets (FMDs) combined with standard treatments are predicted to increase the ability of the latter to be
curative or, at least, to delay the emergence of resistant cancer cell clones. In addition, cycles of fasting or FMDs are anticipated to reduce treatment toxicity ,
possibly switching G3 and/or G4 TEAEs to less severe G1 and/or G2 TEAEs, and to help patients maintain their quality of life throughout therapy.
primarily in patients who are diagnosed
with breast or prostate cancer63,65–68. These
are either one- arm clinical studies to assess
FMD safety and feasibility or randomized
clinical studies focusing either on the effect
of the FMD on the toxicity of chemotherapy
or on the quality of life of patients during
chemotherapy itself. Altogether, these
studies have now enrolled over 300 patients,
and their first results are expected to become
available in 2019.
Challenges in the clinic. The study of
periodic fasting or of FMDs in oncology
is not devoid of concerns, particularly
in relation to the possibility that this
type of dietary regimen could precipitate
malnutrition, sarcopenia and cachexia
in predisposed or frail patients (for
example, patients who develop anorexia
as a consequence of chemotherapy)18,19.
However, no instances of severe (above
grade 3) weight loss or of malnutrition
were reported in the clinical studies of
fasting in combination with chemotherapy
published as of now, and those patients who
did experience a weight loss during fasting
typically recovered their weight before the
subsequent cycle without detectable harm.
Nevertheless, we recommend that periodic
anorexia and nutritional status assessments
using gold- standard approaches18,19,146–150
should be an integral part of these
studies and that any ensuing nutritional
impairment in patients undergoing fasting
and/or FMDs is rapidly corrected.
Conclusions
Periodic fasting or FMDs consistently show
powerful anticancer effects in mouse cancer
models including the ability to potentiate
chemoradiotherapy and TKIs and to trigger
anticancer immunity. FMD cycles are more
feasible than chronic dietary regimens
because they allow patients to consume
food regularly during the FMD, maintain
a normal diet between cycles and do not
result in severe weight loss and possibly
detrimental effects on the immune and
endocrine systems. Notably, as standalone
therapies, periodic fasting or FMD cycles
would probably show limited efficacy against
established tumours. In fact, in mice, fasting
or FMDs affect the progression of a number
of cancers similarly to chemotherapy, but
alone, they rarely match the effect obtained
in combination with cancer drugs which
can result in cancer- free survival11,59. Thus,
we propose that it is the combination
of periodic FMD cycles with standard
treatments that holds the highest potential
to promote cancer- free survival in patients,
as suggested by the mouse models11,59 (Fig. 3).
This combination may be particularly
potent for several reasons: first, cancer
drugs and other therapies can be effective,
but a portion of patients do not respond
because cancer cells adopt alternative
metabolic strategies leading to survival.
These alternative metabolic modes are much
more difficult to sustain under fasting or
FMD conditions because of the deficiencies
or changes in glucose, certain amino acids,
hormones and growth factors, as well as in
other unknown pathways leading to cell
death. Second, fasting or FMDs can prevent
or reduce resistance acquisition. Third,
fasting or FMDs protect normal cells and
organs from the side effects caused by a
wide variety of cancer drugs. On the basis of
preclinical and clinical evidence of feasibility,
safety and efficacy (at reducing IGF1,
visceral fat and cardiovascular risk factors),
FMDs also appear as a viable dietary
approach to be studied in cancer prevention.
An important future challenge will be
to identify those tumours that are the best
candidates to benefit from fasting or FMDs.
Even in cancer types that are apparently less
responsive to fasting or FMDs, it may still
be possible to identify the mechanisms of
resistance and to intervene with drugs able
to revert that resistance. Conversely, more
caution should be adopted with other types
of diets, especially if high in calories, as they
could lead to exacerbated and not inhibited
growth of certain cancers. For example,
the KD increases growth of a melanoma
model with mutated BRAF in mice123, and
it was also reported to accelerate disease
progression in a mouse AML model72.
Furthermore, it is essential to apply FMDs
with an understanding of the mechanisms
of action, since their potency if applied
incorrectly could generate negative effects.
For example, when rats were fasted and
treated with a potent carcinogen before
refeeding, this resulted in the growth of
aberrant foci in liver, colon and rectum
when compared with non- fasted rats151,152.
Although the mechanisms involved in this
effect are not understood, and these foci
may have not resulted in tumours, these
studies suggest that a minimum period of
24–48 hours between the chemotherapy
treatment and the return to the normal
diet is important to avoid combining
the regrowth signals present during the
refeeding after fasting with high levels of
toxic drugs such as chemotherapy.
The clinical studies of fasting or FMD in
patients undergoing chemotherapy support
its feasibility and overall safety52,53,58,61. In a
small- size randomized trial that enrolled 34
patients, an FMD helped patients maintain
their quality of life during chemotherapy
and reduced fatigue61. In addition,
preliminary data suggest the potential of
fasting or FMDs to reduce chemotherapy-
induced DNA damage in healthy cells in
patients52,53. Ongoing clinical studies of
FMDs in patients with cancer63,65–68 will
provide more solid answers as to whether
prescribing periodic FMDs in combination
with conventional anticancer agents helps
improve tolerability and activity of the latter.
It is important to consider that FMDs will
not be effective in reducing the side effects of
cancer treatments in all patients and neither
will they work to improve the efficacy of all
therapies, but they have great potential to
do so at least for a portion and possibly for
a major portion of patients and drugs. Frail
or malnourished patients or patients at risk
of malnutrition should not be enrolled in
clinical studies of fasting or FMDs, and
patient nutritional status and anorexia
should be carefully monitored throughout
clinical trials. An appropriate intake of
proteins, essential fatty acids, vitamins and
minerals combined, where possible, with
light and/or moderate physical activity
aimed at increasing muscle mass should be
applied between fasting or FMD cycles in
order for the patients to maintain a healthy
lean body mass18,19. This multimodal dietary
approach will maximize the benefits of
fasting or FMDs while at the same time
protecting patients from malnutrition.
Alessio Nencioni1,2, Irene Caffa1, Salvatore Cortellino3
and Valter D. Longo3,4*
1Department of Internal Medicine and Medical
Specialties, University of Genoa, Genoa, Italy.
2IRCCS Ospedale Policlinico San Martino, Genoa, Italy.
3IFOM, FIRC Institute of Molecular Oncology, Milano,
Italy.
4Longevity Institute, Leonard Davis School of
Gerontology and Department of Biological Sciences,
University of Southern California, Los Angeles, CA, USA.
*e- mail: vlongo@usc.edu
https://doi.org/10.1038/s41568-018-0061-0
Published online 16 October 2018
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Acknowledgements
This work was supported in part by the Associazione Italiana
per la Ricerca sul Cancro (AIRC) (IG#17736 to A.N. and
IG#17605 to V.D.L.), the Seventh Framework Program
ATHERO- B-CELL (#602114 to A.N.), the Fondazione
Umberto Veronesi (to A.N. and V.D.L.), the Italian Ministry of
Health (GR-2011-02347192 to A.N.), the 5 × 1000 2014
Funds to the Istituto di Ricovero e Cura a Carattere Scientifico
per l’Oncologia (IRCCS) Ospedale Policlinico San Martino (to
A.N.), the BC161452 and BC161452P1 grants of the Breast
Cancer Research Program (US Department of Defense) (to
V.D.L. and to A.N., respectively) and the US National Institute
on Aging–National Institutes of Health (NIA–NIH) grants
AG034906 and AG20642 (to V.D.L.).
Author contributions
V.D.L. substantially contributed to discussion of content,
wrote the manuscript and reviewed and/or edited it before
submission. A.N. researched data for the manuscript, sub-
stantially contributed to discussion of content and wrote the
manuscript. I.C. and S.C. researched data for the manuscript
and reviewed and/or edited the manuscript before
submission.
Competing interests
A.N. and I.C. are inventors on three patents of methods for
treating cancer by fasting- mimicking diets that are currently
under negotiation with L- Nutra Inc. V.D.L. is the founder of
L- Nutra Inc.
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional
claims in published maps and institutional affiliations.
Reviewer information
Nature Reviews Cancer thanks O. Yilmaz, C. C. Zhang and the
anonymous reviewer for their contribution to the peer review
of this work.

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