Fasting can be good for your health — if you do it right.

Published: August 2, 2016 | Updated: November 26, 2019

In the 18th century, Benjamin Franklin wrote that “to lengthen thy life, lessen thy meals.” Researchers now say he might have been on to something.

Franklin didn’t give it a name, but scientists, physicians and dietitians are now giving more attention to what they call “intermittent fasting.”

“Most people hear the word ‘fasting’ and think no food. But intermittent fasting refers to the practice of alternating days with lower calories or delayed meals with the regular pattern of meals,” said Jeanne Thompson, M.D., internal medicine, Norton Weight Management Services.

Dr. Thompson says that intermittent fasting is going a longer period of time with very few or no calories.

Intermittent fasting is safe if you follow one of these three general methods:

1. Eight-hour daily eating window. This means that you restrict eating to a specific window of time, like 8 a.m. to 4 p.m. or noon to 8 p.m. A popular method is to skip breakfast, which allows you to include sleep in your fasting cycle. Studies of time-restricted eating practices in animals and humans have suggested that it may lower cancer risk and help people maintain their weight.
2. Alternate day or every other day fasting. Eat normally on one day, then restrict to about 500 calories — roughly the equivalent to a light meal — on the next day.
3. 5:2 method. Eat normally for five days, then restrict to 500 calories for two days. Celebrity trainer Bob Harper, talk show host Jimmy Kimmel (who lost a significant amount of weight) and a BBC documentary called “Eat, Fast and Live Longer” have popularized this approach.

“Intermittent fasting is not starving yourself. Instead it’s repositioning when we eat and the duration between meals,” Dr. Thompson said.

She adds that although it seems logical that people would overeat on the days when they don’t fast, research shows that often is not the case.

A flurry of recent research has found several health benefits of intermittent fasting, from weight loss to slowed aging. Studies have shown that the result of fasting can protect against age-related cognitive delay and neurodegenerative diseases such as Alzheimer’s and epilepsy. It also may help regulate insulin levels.

Mark Mattson, senior investigator, National Institute on Aging, says that fasting challenges your brain in a way that’s similar to exercising muscle.

In addition, an analysis of six studies that took place from 1975 to 2014 found participants were able to successfully lose weight and maintain that weight loss at a better rate than other methods.

Though research is backing anecdotal claims from both 18th and 21st century devotees, Dr. Thompson has a word of caution.

“Fasting, or any restriction of calories away from the norm, is not for everyone,” she said.

Those who have low blood sugar (hypoglycemia), diabetes or are on certain medications should not fast, as prolonged periods of little to no calories can be uniquely damaging to them.

If you are considering fasting to reach our health goals, first consult with a health professional to help you design a plan that ensures you are eating the right foods on fasting and nonfasting days.

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