Hungry for Health: Fasting's Medical Benefits

John Watson


July 12, 2018

In This Article

Why Fasting May Work

When our bodies enter a fasting state, we deplete the stores of glucose in our livers and convert to fat-derived ketone bodies. Depending on your physical output during the fasting period, you can enter a ketogenic state within hours.

Proponents of fasting as a dietary intervention will probably have little difficulty communicating why there might be benefits to substituting ketones for glucose and the myriad negative health effects it can cause when poorly regulated. However, they may find more resistance in overcoming the common belief that fasting slows down metabolic rates, which raises the question: If your body is compensating for lack of food in this manner, wouldn't this simply offset or limit any advantages to be gained?

In fact, this long-standing assumption began to change toward the end of the 20th century, when research emerged indicating that fasting for durations of a few days had the opposite effect of increasing metabolism.[3,4] The full spectrum of physiologic mechanisms contributing to increased metabolism during early food restriction is complex, involving such factors as circadian rhythm and upticks in the fat-burning hormone norepinephrine.[3,5] However, the utility of this approach is borne out by clinical studies of metabolic outcomes. A recent review[6] identified 16 such studies that, although primarily consisting of cohorts of less than 50 patients, nonetheless show different fasting regimens produced notable decreases in glucoregulatory markers, lipids, inflammatory markers, and weight.

The increasing popularity of fasting diets among the general public may also be due to how easily these align with the consensus that there is something amiss with the modern diet. Although our bodies retain the ability to get by quite capably for long periods in a ketogenic state, we happen to live in a society where the predominant eating schedule makes doing so extremely difficult.

"If you look back in the literature, the recommendation that we eat three meals a day with some snacking on top is mainly based on studies of diabetics, and the notion was that you don't want to have big spikes in glucose," said Mark P. Mattson, PhD, chief of the Laboratory of Neurosciences at the National Institute on Aging, and professor of neuroscience at Johns Hopkins University in Baltimore, Maryland. "But it turns out that intermittent fasting actually improves glucose regulation in both animals and humans."

If you consider that our bodies evolved over millennia to function in one way (hunter-gatherer systems defined by periodic food scarcity) but have been wrenched into another system in a relatively short period, it takes only a small mental leap to see how this may play a role in our contemporary crisis of food-related illnesses.

The epidemic of obesity...occurred in the past 40 years with the eating pattern of three meals a day plus snacks.

"The epidemic of obesity, including childhood obesity, occurred in the past 40 years with the eating pattern of three meals a day plus snacks," Mattson added. "So clearly, that is not necessarily a healthy eating pattern. If people can avoid overeating by skipping meals, once they adapt to that, it can only be a good thing."


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