Fasting Can Be Good for You

By Temma Ehrenfeld @temmaehrenfeld
August 21, 2015

Animals and early humans didn’t eat every day.

We’ve all heard the rule that skipping meals, especially breakfast, is a bad way to diet. But experienced dieters know that alternating periods of more or less food is also helpful. After all, our three-meals-a day routine and environment peppered with vending machines is a vast change from our savannah origins.

In fact, some research suggests that semi-fasting routines — for example, eating only 500 calories for 16 hours, twice a week — could be healthier than eating consistent meals every day. The reason is that we once ate more like lions do — carnivores kill and eat prey a few times a week or less often. Today’s hunter-gatherers also can’t count on a steady supply of food. Our overall makeup of genes today probably derives from the Late-Paleolithic era, when we had to expend lots of energy to acquire our food and cycled between feast and famine. Our metabolisms may expect us to live off berries for a stretch until we nail some antelope-meat. We also ate during daylight hours, not round the clock.

Now that we’re rich in food options, why live like we’re poor? Because wild animals and modern hunter-gatherers rarely suffer from obesity, diabetes, and heart disease — the epidemics of overfed civilization.

A growing body of research suggests that diet advice should shift towards recommendations about timing, according to Satchidananda Panda, PhD, an associate professor of regulatory biology at the Salk Institute for Biological Studies in San Diego, California, and his co-authors. His team suggests further research into the effects of eating only 500 calories every other day, eating that much two days a week, or skipping breakfast and lunch for several days a week. On routines like these, they report, people can feel energized and become more sensitive to insulin, a desirable result to prevent diabetes — more so than if they cut back calories every day and lost the same amount of weight. People have seen fewer symptoms of asthma and arthritis, possibly because breaks from peak consumption reduce inflammation and give the body a chance to rejuvenate and repair. For example, “fasting ‘cleanses’ cells of damaged molecules and organelles,” the coauthors write. Data from animal studies suggests that intermittent eating could counteract multiple sclerosis, lupus erythematosus, and type 1 diabetes. Fasting also makes the body burn fat for energy, which can lead to weight loss. Too much fasting, though, can break down your body’s muscle protein.

Emulating our hunter-gatherer forbears would also mean eating earlier in the day. A variety of research suggests that eating late makes it harder to lose weight. Shifting to more calories at breakfast and less at dinner, for example, improves insulin sensitivity.  

Studies with mice suggest that eating within a 12-hour window is best, which means that a 7:30 a.m. breakfast would effectively keep you away from food throughout the evening. In a human study, people who tended to eat at night ate about 300 more calories each day. After three years, they had gained 14 pounds, on average. People who didn’t eat near bedtime had gained only 4 pounds.

You may have heard of the Paleo Diet, which cuts out foods hunter-gatherers didn’t eat, including grains, dairy, and legumes. In this approach, you eat more fruits, vegetables, nuts and seeds, nut oils, fish, and grass-fed lean meat or game. And yes, it’s absolutely clear that Americans will benefit from eating more fruits and vegetables, and, of course, less junk food with added sugar, fats, and refined carbs.

It remains unclear, however, whether anyone should avoid grains, beans, and dairy. Early humans may have eaten wild grains before we became farmers, and our bodies have evolved since then to break down dietary starch. All that said, you might rethink the idea that you’re “starving” if you feel a little hungry. Instead of grabbing a candy bar, you might eat a few nuts or seeds, drink some water, and remember that you’re only here because a prehistoric man survived a drought. 


August 21, 2015

Reviewed By:

Janet O’Dell, RN

Easy access to health records and personalized content.