The Evidence for Intermittent Fasting

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I have been advocating intermittent fasting (IF) to my patients for some time now after having tried it out for myself with impressive results (for details see this post).  The problem with most diets that you read on the internet is that they make broad claims but are usually without proof that they work.  The strategy they typically employ is taking a few scientifically proven facts that they then exaggerate and misapply to other contexts. They use the science to make them sound credible but oversimplify and overgeneralize.

The way the scientific process works is that small bits of evidence accumulate from multiples studies done over a long time.  Each of these pieces of information only provides a small piece of the overall picture.  That’s why you can never rely on a media report of a single study, its too narrow a focus.  One of the hallmarks of the scientific method is replication and a single study can’t provide that. The process of science changes and evolves with time.

NEJMThe reason I advocated IF were listed in the post I linked to above but I was quite excited to see a review in the New England Journal of Medicine which summarizes the published articles to date.   This article published in the most prestigious medical journal in the world officially takes IF explains why it is not just a “fad” diet and lends it the credibility of a strategy with broadly proven benefits.  I thought I would summarize some of the highlights.

The rationale for IF is that our bodies are not designed for three regularly spaced,
large meals (plus snacks) every day in combination with a sedentary lifestyle.  Much of the data comes from animal studies the findings of which are not always found in humans but the accumulation of evidence is compelling.  The full picture is coming into view.

Studies in animals and humans have shown that many of the health benefits
of IF are not simply the result of weight loss.  Intermittent fasting leads to responses in cells that improves glucose regulation, increases stress resistance, and suppress inflammation.  During fasting, cells activate pathways that enhance intrinsic defenses against chemical stresses and those that remove or repair damaged molecules.  In animals IF has been shown to have a beneficial impact on wide range of chronic disorders, including obesity, diabetes, cardiovascular disease, cancers, and neurodegenerative brain diseases.

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When you don’t eat for beyond about 14 hours your body starts making chemicals called ketone bodies which provides a major source of energy for the body, especially the brain.  This process is called ‘metabolic switching’.  Ketone bodies are not just fuel used during periods of fasting; they are potent signaling molecules with major effects on cell and organ functions.  They regulate the activity and production of many proteins and molecules that are known to influence health and aging.   They also stimulate genes that are known to be important for brain health with implications for psychiatric and neurological diseases.  These benefits are over and above the benefits of the weight loss they induce.  As an added benefit, they suppress appetite as well. 

The Intermittent Fasting Detox

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Many people are concerned about exposure to various dangerous environmental toxins.  It turns out the greatest producer of harmful toxins that can threaten your health is your own body.  When exposed to overeating and sedentary lifestyle produces toxins as bad or worse as can be found in most industrial factories.  On the cellular level repeated exposure to fasting periods leads to increased production of the cells’ natural defenses leading to improved function and resistance to a broad range of potentially damaging toxins.  In addition to decreasing production IF also improves cells’ ability to remove accumulated toxic substances.  These defenses and improved toxin clearance are suppressed in those who overeat and are sedentary.

Impact on Overall Health

After nearly a century of research on caloric restriction in animals reduced food intake clearly increases life span.   Trials have shown that IF has a more pronounced effect on waist circumference than other diets.  Emerging evidence suggests that intermittent fasting may enhance athletic performance as well.

Impact on Brain Function and Neurologic Disease

Studies in animals show that IF improves brain function and memory and reverses the adverse effects of obesity on learning and memory.  One study of older adults on a short-term regimen of caloric restriction showed improved verbal memory. Another study involving overweight adults with mild cognitive impairment showed that 12 months of caloric restriction led to improvements in verbal memory, executive function, and global cognition.  A large recent clinical trial showed that 2 years of daily caloric restriction led to a significant improvement in working memory.

plato-fasting-quoteThere is strong evidence that alternate-day fasting can delay the onset and progression of disease in animal models of Alzheimer’s and Parkinson’s disease.  Studies in humans are lacking, however.  Two small pilot studies showed that patients with multiple sclerosis who adhere to IF regimens have reduced symptoms in as short a period as 2 months

Impact on Chronic Disease

IF improves blood pressure; resting heart rate; cholesterol and triglyceride levels, and insulin resistance.  In addition, intermittent fasting reduces markers of systemic inflammation and oxidative stress that are associated with heart disease.  Improvements in cardiovascular health indicators typically become evident within 2 to 4 weeks after the start of alternate day fasting and then dissipate over a period of several weeks after resumption of a normal diet.

Impact on Cancer

Numerous studies in animals have shown that daily caloric restriction or alternate-day fasting affects metabolism in cancer cells reducing the occurrence of spontaneous tumors while increasing their sensitivity to chemotherapy and radiation.  Trial in humans are ongoing.

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The Challenges

 

There is much evidence for the benefits of IF but it is not easy to start.  Once you get going, however, it gets easier with time.  A diet of three meals with snacks every day is so ingrained in our culture that a change in this eating pattern will rarely be contemplated even though there is no evidence that three meals a day is necessary.  In fact, all the evidence supports the fact that three meals a day is harmful.

Summary

There is a large and growing body of evidence proving that intermittent fasting has multiple broad  benefits for many health conditions.  More studies are ongoing but  the data listed above is the reason I advocate IF as the most effective way to lose weight and improve overall health.

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