Fasting is one of the oldest practices in history, used across the globe as part of religious practices as well as a form of alternative treatment in traditional medicine to promote healing and prevent future disease. Hippocrates, himself, believed that fasting empowered the body to heal itself.
Many of the great prophets of the world’s oldest religions including Jesus, Buddha, and Mohammed fasted for mental and spiritual clarity, and fasting has even been used as a form of political protest as demonstrated by Gandhi’s 21 day fast to foster peace and freedom in India.
Related - Modified Fasting Diet for Big Eaters
Yes, fasting is an integral part of human history that has helped us survive periods of famine, crop disease, and gain clarity of mind and spirit. Today, fasting is still embraced in many religions on cultures, but due to some emerging research, it appears that fasting may be being investigated for its ability to treat, and potentially cure, cancer.
Let’s take a look at some of the recent claims that dry fasting cures cancer.
What is Dry Fasting?
Before getting into the claims of fasting curing cancer, let’s give a brief overview of what fasting is. Believe it or not, there are two types of fasting:
- Wet fasting
- Dry fasting
Dry fasting is a form of fasting that does not allow any food or water intake. This is a more extreme and advanced form of conventional fasting (wet fasting) that allows water but prohibits the intake of food. The reasoning behind dry fasting is that proponent believes the removal of water may “accelerate” some of the protective effects that occur during a water fast, including those affecting metabolic health and inflammation.
Dry fasting is less frequently used than wet or water fasting due to the belief that it’s more dangerous due to the lack of water, but dry fasts are actually quite common in certain parts of the world. For example, during Ramadan, Muslims dry fast during daylight hours, which is typically 12 hours, but in some polar regions, it can be as long as 22 hours!
Some of the benefits attributed to fasting (as well as calorie restriction) include: 
- Increased lifespan (longevity)
- Increased neurogenesis
- Regulated insulin levels
- Reduced oxidative markers
- Improved neural plasticity
- Decreased inflammation
- Lower blood pressure
- Balanced blood sugar levels
Recently, a new claim has been made in regards to the benefits of fasting - it can cure cancer.
So, let’s take a deeper look at our biology and see how fasting impacts the inner workings of our body to uncover the truth about this claim.
Cancer, Fasting, and Human Biology
The topic of fasting, calorie-restriction, and time-restricted feeding has been studied for well over 100 years, particularly in regards to extending lifespan. Most of the research to this point has been conducted in mice and fruit flies, but there have been a fair amount of human trials as well that have shown a positive correlation between fasting and aging.
Specifically, with fasting and calorie-restriction comes reductions in markers of diabetes and atherosclerosis along with reductions in inflammatory markers such as tumor necrosis factor (TNF) and C-reactive protein (CRP).
So, what exactly happens inside the body when its deprived of nutrition?
Well, in response to starvation, an organism diverts energy to its various protective systems so as to reduce any damage that might reduce its “fitness”. These systems are also believed to impact lifespan, as well as decrease cancer risk. In fact, according to a recent review from researchers at the University of Southern California, calorie-restriction may be one of the most effective weapons we have for preventing cancer: 
“Data from experimental and epidemiological studies indicate that excessive adiposity due to excessive energy intake and minimal physical activity increase the risk of developing cancer. In contrast, calorie restriction without malnutrition, and possibly protein restriction, prevent cancer.” 
Fig. 2 CR causes several key metabolic/hormonal adaptations, that alter the expression of several genes and signaling pathways (up-regulation of certain genes/signaling pathways and down-regulation of others as indicated by the arrows), which produce major cellular adaptations (e.g. a reduction in cell proliferation, increased removal of damaged organelles or cells via autophagy or apoptosis, up-regulation of DNA repair systems and genomic stability) that result in a reduced cancer incidence. 
As we discussed up top, calorie restriction decreases inflammatory cytokines and oxidative stress, but it also reduces levels of several anabolic hormones and growth factors. It also upregulates autophagy (cell destruction and recycling) and several DNA repair processes. 
One of the critical growth factors we alluded to is insulin-like growth factor-1 (IGF-1), which plays a major role in cancer (promoting tumor development).  Research has noted that when protein is restricted (as part of calorie restriction) IGF-1 levels are reduced, which is interesting to note, as cancer patients are often recommended to maintain a high protein intake during treatment. 
Now, during fasting, your body is trying to conserve energy. It enjoys being alive and will do anything and everything to keep it going. In this life-preserving effort, your body goes through three “phases” when searching for energy. The first phase uses up stored glycogen for energy. This phase lasts 10 hours or more depending on your glycogen levels.
After glycogen has been depleted, the body turns to stored fat and breaks it down into glycerol and fatty acids, which are used to create ketones. These ketones provide energy for the brain and body (as seen with ketogenic diets), and this phase can last for several weeks if you’re a bigger individual.
The final phase starts when the fat reserves are exhausted, catabolism - muscle tissue is broken down to continue to sustain gluconeogenesis.
But, the body isn’t just robbing you of your gains and unwanted fat. It also recycles a lot of immune cells that aren’t needed, especially the ones that are damaged.
Along with these immune cells comes a decrease in several inflammatory markers, including: 
- Tumor Necrosis Factor-alpha (TNF-α) - A signaling protein involved in systemic inflammation and has been shown to increase chances of cancer and other degenerative diseases, including Alzheimer’s.
- C-Reactive Protein (CRP) - Elevated levels of this protein are correlated with increased risk of cardiovascular disease, hypertension, and diabetes.
- Interleukin 1 beta (IL-1b) - Lymphocyte activating factor and mediator of inflammation that has been linked to heart failure.
- Interleukin 6 (IL-6) - Pro-inflammatory cytokine and an anti-inflammatory myokine that’s associated with a greater risk of diabetes and various forms of cancer.
- CXC Chemokines - Proteins that bind to cytokines and cause inflammation when unregulated.
Dry fasting may also promote cancer-killing T-cells and decrease leukocytes (immune cells), which subsequently reduces the progression of inflammatory diseases.[9,13] Fasting also lowers insulin, which many know as the hormone responsible for shuttling nutrients into muscle cells after a workout, but it is also a powerful promoter of cancer cell growth.
Essentially, doctors believe that be fasting, you’re ultimately “starving” the cancer cells of the nutrients they need to thrive and multiply, which is primarily sugar (glucose). Without sufficient nutrients, the cancer cells are stripped of their protective coating, making them more easily recognized and targeted by your body’s immune system.
Now let’s take a look at the studies that have been conducted to see if fasting can offer any benefit from protection against cancer.
Fasting Cancer Research
Animal & Cell Culture Studies
Calorie restriction and fasting in regards to cancer was first studied in 1909 when the researcher Carlo Moreschi showed that calorie restriction stunted tumor growth in mice. Since that time, volumes of work have been published demonstrating that calorie restriction has beneficial effects on reducing tumor growth in various animals.
Other studies conducted have noted that when calorie restriction was instituted by 12 months of age, lifespan was significantly increased, and incidence of cancer was reduced by 50%!  However, it should be noted that cancer cells are pretty clever, and they’ve been shown to mutate and become resistant to the effects of calorie restriction. 
A 1988 study using 48 rats was one of the earliest ones to utilize full fasting (calorie restriction allows for very minimal food). In this study, one group of rats ate as they desired, while the other group was put on an alternate day fasting protocol (one day on food, one day “off” -- fasting). 
After one week of following this diet, both groups were injected with breast cancer (isn’t that pleasant...). Nine days after injection, ⅔ of the fasted rats (24) were still alive, while only 5 of the rats eating “ad libitum” were still cranking away on their wheel.
In the late 90s, a researcher by the name of Dr. Valter Longo started investigating the effects of fasting on cellular resistance to oxidative stress. With the understanding that chemotherapy kills cells (good cells and bad ones) by inducing oxidative stress, and knowing that fasting activates certain “survival” mechanisms in healthy cells, but not cancer cells, he held a study to see if fasting might protect healthy cells in mice subjected to chemotherapy. 
For the study, tumor-infected mice were either fed normally or fasted for 48 hours leading up to a chemotherapy treatment. Half of the mice who ate normally survived the chemo treatment, while the other half died. Here’s where things get interesting…
The group of mice who have fasted for 48 hours prior to chemotherapy ALL SURVIVED.  Longo and colleagues have also observed that “starvation-dependent stress” (i.e. stress induced by fasting) protects normal, healthy cells, but not cancer cells, against the effects of chemotherapy. 
Fig.1 Fasting provides differential stress resistance (DSR) to chemotherapy. The investment of the finite energy available in a cell or an organism is efficiently balanced between growth/reproduction and maintenance/repair. 
Furthermore, researchers have also shown that “modified” fasting, whereby mice consume 15% of their normal calories on fasting days, decreased rate of tumor cell growth.  What’s really interesting is that the “modified” fasting approach was found to be more effective than 100% abstinence from food!
Additional research from 2008 noted that fasting retards tumor growth, and it also “sensitizes” cancer cells (multiple types) to the effects of chemotherapy.  In other words, fasting prior to undergoing chemo may enhance the effects of the treatments in killing cancer cells, while also protecting your healthy cells.
But, these studies are only in isolated cell cultures and animals (rats), what happens when human cancer patients undertake a fast?
How does that affect cancer progression and the effects of chemotherapy?
Recently, Longo et al investigated the effects of fasting for three days prior to chemotherapy treatment. 20 patients participated in the study with an average age of 61 years old. They were divided into three groups that fasted for 24, 48, and 72 hours prior to chemotherapy.
Researchers found that fasting for 72 hours (3 days) improved the patients’ resistance to chemotherapy treatments. Patients in the 48-hour fasting group showed less DNA damage than those who had fasted for only 24 hours. Now, it should be noted that this was a very small study group, but the results are extremely interesting, to say the least.
An older case study conducted by Longo and friends tracked a woman with breast cancer who underwent four rounds of chemotherapy.  Prior to her first round of chemo, she fasted for six days, and aside from fatigue and dry mouth, she fell well enough to continue working.
However, for the next two rounds of chemotherapy, she DID NOT fast and reported feeling awful following treatment and could not work. She also complained of severe pain, nausea, and fatigue. The first round came during a six-day fast. 
Other than dry mouth, fatigue, and hiccups, she felt well enough to continue working. For the second and third rounds of chemo, she didn’t fast. She felt awful the entire time, couldn’t work and complained of severe nausea, fatigue, and pain.
For the fourth and final round of chemotherapy, the woman decided to return to fasting and following treatment, she showed improved white blood cell, neutrophil, and platelet counts. 
This echoes the results of another recent case study that suggests that fasting potentially combats cancer directly.  A woman with non-Hodgkin’s lymphoma undertook a 21-day water fast that significantly reduced lymph size.
Following the fast, she adopted a plant-heavy diet focused on whole foods, and 9 months after making the switch, her lymph notes remained a normal size.  She decided to fast for the fourth and final round, which went as well as the first round. Fasting also improved her biomarkers, including white blood cell, platelet, and neutrophil counts.
Based on these results, Longo has begun to promote the “fasting-mimicking diet” (FMD) which is a low-protein, high-moderate-carb, moderate-fat diet. The diet is a 5 day “quick fix” fast that allows you to get the benefits of fasting without having to actually completely abstain from food for a prolonged period of time. In reality, the fasting-mimicking diet is more akin to calorie-restriction than a hard fast.
On the first day of the diet, you’ll consume 1090 calories, consisting of 10% protein (27 grams), 56% fat (68 grams), and 34% carbohydrates (93 grams). The following four days only allow you to consume 725 calories, comprised of 9% protein (16 grams), 44% fat (35 grams), and 47% carbohydrates (85 grams).
Regarding the fasting-mimicking diet, Dr. Longo has said:
“But by undergoing a fasting-mimicking diet, you are able to let the body use sophisticated mechanisms able to identify and destroy the bad but not good cells in a natural way.” 
Concerns with Fasting and Calorie Restriction
While the research regarding fasting and its effects on human metabolism and cancer cell progression is promising, there are still several concerns that need to be mentioned with calorie restriction and fasting.
The first one, obviously, is weight loss. Anytime you deprive the body of food for a considerable amount of time, it’s going to start feeding on its energy stores to fuel the variety of processes it needs to sustain life. Research has shown that as much as 15-20% weight loss can occur as a result of calorie restriction. While this might seem like a great idea for those who are overweight or obese, if you are underweight or at a healthy weight, it may lead to malnourishment and nutrient deficiencies.
You may also suffer a significant drop in blood pressure when you stand, which is known as orthostatic hypotension. This is also common when fasting.  Furthermore, if you’re currently prone to migraines or headaches, or dealing with dry eye syndrome, cataracts, or glaucoma, it’s best to avoid dry fasting as it can exacerbate the symptoms of these conditions.
If you’re concerned about dehydration when dry fasting (a valid concern when you’re not drinking any water), consider this research conducted in Malaysian Muslims which showed that total body water content was conserved during a dry fast. Essentially, the body compensated for the lack of water intake by minimizing water excreted from the body, creating an “internal balance” or sorts. 
So, is dry fasting a “cure” for cancer? Science hasn’t conclusively proven that to be the case yet. However, current research does suggest that fasting for 1-3 days leading up to chemotherapy is safe and may help protect the healthy, normal cells in your body from chemotoxicity. This means that dry fasting could be used as an effective adjunct treatment to chemotherapy, but by no means is it a replacement for chemotherapy or “cure” for cancer.
The research is still ongoing, but results published thus far make it worthwhile to incorporate fasting into your daily life if you’re seeking to improve other markers of health and potentially combat the effects of aging.
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