Why Fast? Part Two – Cancer

“Everyone has a physician inside him or her; we just have to help it in its work. The natural healing force within each one of us is the greatest force in getting well. Our food should be our medicine. Our medicine should be our food. But to eat when you are sick is to feed your sickness.” – Hippocrates

and:

“Instead of using medicine, rather fast a day.” – Plutarch

or even:

“No kibble today, thanks. I’m feeling a bit under the weather.” – Fido

For thousands upon thousands of years (during most of which overweight, let alone obese, people were fairly rare), therapeutic fasting was a common protocol for the healing of many a malady. From famous sages like Plato, Aristotle, and the aforementioned Hippocrates and Plutarch to cancer patients unable to eat during chemotherapy to pet dogs and cats who suddenly lose once-voracious appetites upon falling ill, it seems like the natural response to – and perhaps therapy for – major illness is to stop eating for a while.

Now, “natural” is not always good. “Is” does not necessarily imply “ought.” But I think the persistence of this phenomenon throughout nature demands that we look a little more closely into whether or not there’s something to it. From babies putting items they found on the ground into their mouths to introduce novel bacteria to their bodies, to weight lifters craving meat after a hard workout to introduce protein to their hungry muscles, to pregnant women experiencing strong food aversions to minimize the chance of introducing a toxin or poison to the growing fetus, I’m generally of the opinion that there’s usually a physiological explanation for most of our odd cravings and behaviors. I see no reason why a sudden lack of appetite wouldn’t have a similar explanation – especially one that transcends species. What if skipping meals for a day or two kickstarted internal healing in some way? Is that really so outlandish? You already know where I stand on the importance of lessons learned from watching our animal companions, and I think this time is no different.

Luckily for us, we aren’t just flailing around and making guesses. Modern science has deigned research into the phenomenon, particularly regarding cancer, worth pursuing. According to Valter Longo, a cancer researcher from USC, “normal cells” go into survival mode during starvation. They display “extreme resistance to stresses” until the “lean period” ends, much like an animal in hibernation mode. Cancer cells, on the other hand, are always “on.” Their “goal” is to grow and reproduce and consume resources. For cancer cells, there is no novel survival mode to switch on. If this is the case, fasting should both improve our resistance to cancer and our body’s ability to survive it (and the treatments used against it, like chemotherapy).

Though human trials are scant (you can’t exactly inject people with cancer cells and then try out different therapeutic protocols, the animal research is intriguing. Let’s take a look into the literature, shall we?

Animal Trial

In one of the earliest studies, forty-eight rats were split up into two groups of twenty-four. One group ate ad libitum for a week, while the other group underwent alternate day fasting. After one week of the various dietary protocols, both groups were injected with breast cancer. At nine days post-injection, 16 of 24 fasted rats remained alive, while just five of 24 ad-libitum fed rats lived. At ten days post-injection, only three of the 24 ad libitum-fed rats survived; 12 of the 24 fasted rats remained alive. Pretty large disparity, right?

That was in 1988. It wasn’t until the late 90s that more promising research was undertaken. That’s when Longo began studying in earnest the phenomenon of increased cellular resistance to oxidative stress during fasting. Figuring that since chemotherapy exerts its effects on cancer by inducing oxidative stress (to all cells, not just cancerous ones), and fasting triggers survival mode in normal cells but not cancer cells, he conducted a study on mice to determine whether fasting protected the healthy, normal cells from chemotherapy’s side effects while leaving the cancer cells sensitive to the treatment. Tumor-ridden mice were either fasted or fed normally 48 hours prior to a large dose of chemotherapy. Half of the normally-fed mice died from chemotherapy toxicity, while all of the fasted mice survived (PDF). Furthermore, fasting did not improve the survival rate of cancerous cells, meaning it only protected normal, healthy cells.

Research has continued. Longo found that “starvation-dependent stress” protects normal cells, but not cancer cells, against the effects of chemotherapy. Even a “modified” alternate day fasting regimen, in which mice were given 15% of their normal calories on “fasting” days, reduced proliferation rates of tumor cells. This “85%” fasting regimen was even more effective than the full 100%. And most recently, Longo et al found that fasting both retarded the growth of tumors while sensitizing cancer cells to the effects of chemotherapy – across a wide range of tumor types. Most importantly, they concluded that fasting could “potentially replace or augment” certain existing chemotherapy regimens! That’s not some crazy fad diet guru spouting off about ancient traditional wisdom, folks. That’s a cancer researcher.

Human Trial(s)

There has been just one of which I’m aware: a 2009 case study that delivered promising results. Ten cancer patients – four with breast cancer, two with prostate cancer, one each with ovarian, lung, uterine, and esophageal cancers – underwent fasting prior to and after chemotherapy treatment. Fasting times ranged from 48-140 hours prior to and 5-56 hours after; all were affective at reducing side effects of chemotherapy.

In the first case, a 51-year old woman with breast cancer did her first round of chemotherapy in a fasted state of 140 hours. Other than dry mouth, fatigue, and hiccups, she felt well enough to go to work and resume her normal daily activities. For the subsequent two rounds, she did not fast and instead ate her normal diet, and the side effects were extremely pronounced – severe fatigue, diarrhea, weakness, abdominal pain, nausea – and prevented her from returning to work. For her fourth round of chemotherapy, she fasted, and the side effects were again minimized. And it wasn’t just the subjective effects that improved with fasting, but also her physiological markers. Total white blood cell, absolute neutrophil counts, and platelet counts were all highest after the fasting regimens.

More human trials are underway, however. Hopefully we’ll eventually know whether the loss of appetite commonly reported during chemotherapy treatment is a bug or actually a built-in feature (I’m leaning toward the latter, personally).

Other Possible Protective Mechanisms of Prevention

Improved insulin sensitivity. As I showed in last week’s post on fasting and weight loss, intermittent fasting improves insulin sensitivity and reduces insulin resistance. Insulin resistance has been linked to several cancers, including prostate, breast, and pancreatic. Metabolic syndrome, which fasting seems to help prevent and reduce, is linked to cancer in general.

Autophagy. While autophagy – the process by which cells “clean up” cellular “garbage” – has a complex relationship with cancer, it’s generally a positive process that protects cells from excessive oxidative stress. Fasting has been shown to induce “profound” neuronal autophagy, as well as general autophagy.

Fasting versus caloric restriction.

It’s true that caloric restriction appears to offer anti-cancer benefits, but there are a couple ways in which fasting might be superior:

1. Fasting (acute bouts of caloric restriction) is easier than CR (chronic caloric restriction) for most people. As I mentioned in last week’s post, fasting – for some – is just an easier, more natural, more effortless way to reduce your calorie intake. That can pay huge dividends when it comes to weight loss, and it appears likely that it will help with cancer, too. If fasting is easier than constantly counting your calories, fasting is going to work better.

2. Fasting is more effective in a shorter amount of time. Whereas studies on caloric restriction and cancer employ weeks- and months-long CR regimens, studies on fasting and cancer employ hours- and days-long fasting regimens. In most cases, fasting just seems to require far less time to be effective.

It’s an exciting time for fasting and cancer research. While it’s still viewed in most circles as an “alternative” modality, fasting is now being seriously considered as a possible treatment (both adjunct and even primary) for various cancers, including breast and prostate. I can’t wait to see what comes out in the coming years.

Of course, my own feeling is that fasting is both easier and more effective if you have made the transition to a Primal Blueprint way of eating. In other words, when you have up-regulated those fat-burning systems and down-regulated the reliance on glucose, many of the other issues that can make fasting less appealing to “sugar-burners” tend to go away: cortisol levels out, muscle protein is spared, hunger subsides naturally and energy is steady.

What does this mean for you – the person who either has cancer and wants to get rid of it or who doesn’t have cancer and wants to stay that way? Researchers like Valter Longo can’t officially recommend it to cancer patients, but it seems well-tolerated and basically safe. If you or anyone you know has cancer, suggest fasting as a possible strategy. As long as a person keeps their oncologist apprised of the situation and any relevant research on the subject, it might prove helpful. And if you’re currently cancer-free, consider implementing occasional (intermittent) fasts, just to be safe. I know research like the stuff I’ve just outlined has convinced me that it’s definitely worth a shot, and there’s little if any downside.

For those of you readers who currently practice fasting, do the potential cancer benefits motivate and drive you? If you aren’t currently fasting, does this evidence make you want to? Thanks for reading!

Here’s the entire series for easy reference:

Why Fast? Part One – Weight Loss

Why Fast? Part Two – Cancer

Why Fast? Part Three – Longevity

Why Fast? Part Four – Brain Health

Why Fast? Part Five – Exercise

Why Fast? Part Six – Choosing a Method

Why Fast? Part Seven – Q&A

Dear Mark: Women and Intermittent Fasting



About the Author Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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