Science makes a case for healthy fasting

Fasting is sometimes used as a form of protest or within religious practices. But a growing body of research shows that our health may depend on eating more like our ancestors did when food was scarce.

“This is an exciting area,” said Mark Mattson, a neuroscience professor at Johns Hopkins University. “Now there are at least 150 clinical trials of intermittent fasting in humans with various disorders — cancer, diabetes, neurological disorders, et cetera.”

Mattson is part of one of the trials, which is testing two groups of adults over 55 who have obesity and insulin resistance. Mattson, former chief of the neurosciences lab at the National Institute on Aging, said the test group is fasting two days a week, when they consume only 500 calories. The study is examining people who are at risk for Alzheimer’s disease.

“Based on animal studies, we think that it’s possible the intermittent fasting eating pattern can shift those brain biomarkers of Alzheimer’s disease in a favorable direction,” he said.

Mattson said research on fasting being done at the Salk Institute in San Diego takes a different approach when it comes to eating patterns. But it’s very similar in terms of the resulting health benefits.

Emily Manoogian is a staff scientist at Salk, who studies what she calls “time-restricted” eating. The principle is to limit your eating to, for instance, a 10-hour window of time — say from 8 a.m. to 6 p.m. This is based on circadian rhythms, the body’s internal clock, which expects eating and activity to occur when it’s light out.

“Your body functions differently at different times of day,” Manoogian said. “So the way you process food in the middle of the day, when you’re active and you’re going to be using the energy to function throughout the day, is very different from how your body processes food at night when your body expects you to be sleeping.”

And the fast that occurs between dinner and breakfast is crucial for the body to process the sugar and fat you’ve stored away.

“Your body needs to be in at least a mildly fasted state to be able to break down the energy stores that you have. So if you’re constantly eating late into the night, you’re never going to break down your own energy stores,” she said. “Because you need to be fasting for at least 12 hours before you’re really tapping into breaking down fat that you have, and turning it back into energy for your body.”

Mattson says this shift in the body’s use of food stores, from glucose to fat, is a metabolic shift that comes with fasting and is very important to a body’s health. The scientists say research is ongoing but it has shown that fasting can have a preventive effect not only on cognitive diseases like Alzheimer’s but also obesity, diabetes and cardiovascular disease.

“If you look at this from an evolutionary perspective the major driver of evolution was food scarcity — overcoming food scarcity," Mattson said. "Individuals who were successful in competing for limited amounts of food were successful and passed their genes on."

He says fasting and exercise place a mild stress on the nerve cells in the brain, but it’s a good stress.