Intermittent Fasting May Help Support Brain and Body

Some research finds it’s not just what you eat, it’s when you eat it

Candy Sagon

Updated September 28, 2022

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While typical diets are built around restrictive lists of foods that you should and shouldn’t eat, one of the most popular strategies in recent years takes a very different tack. Intermittent fasting focuses on when you should eat, not what.

More of an eating pattern than a diet, intermittent fasting doesn’t exclude specific food groups, such as carbohydrates, fats, sugar or animal protein, which may be part of its appeal. The idea is that by restricting the number of hours we can be munching, we will reduce our calorie intake.

In addition, the science suggests that daily fasting for a long block of time — for example, after dinner ends at 7 or 8 p.m. until around 11 a.m. the next morning — helps reduce the levels of insulin, blood pressure and cholesterol and causes the body to burn off more fat.

It’s also a pattern of eating that is more in sync with the way the human body naturally operates. Our metabolism is programmed for daytime eating and nighttime sleep. Eating at night can throw off this balance, leading to weight gain and a greater risk of diabetes and heart disease, to say nothing of sleep problems, studies show.

For people at midlife and older, there may be additional benefits. Studies of older adults using intermittent fasting suggest that it can help reduce inflammation in some people, and several studies found it was linked to improvements in short-term memory in older adults. Intermittent fasting may also help cells clear out damaged cells, which could potentially improve brain function.

Fasting is nothing new, of course. It’s been practiced throughout history for cultural and religious reasons. The current version took off in 2012 with a documentary by BBC broadcast journalist and physician Michael Mosley called “Eat, Fast, Live Longer,” followed by books like The 5:2 Diet by Kate Harrison and internist Jason Fung’s 2016 bestseller The Obesity Code.”

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The strategies for intermittent fasting generally fall into two categories: a daily window of around eight hours for meals followed by fasting, or the so-called 5:2 weekly method, in which people eat normally for five days, but gradually limit themselves to just 500 to 600 calories on each of two nonconsecutive days.

No matter which strategy you choose, talk to your doctor before trying a fasting plan, stay well-hydrated and choose healthy foods for meals. Those with chronic diseases or who need to take medication at specific times or who have had problems with disordered eating should also take particular care and caution before trying any fasting plan.

Many find the daily meal window method easier to follow than the 5:2 weekly plan where you’re “hardly eating anything two days a week,” Mark Mattson, a neuroscientist with Johns Hopkins University School of Medicine, who has been researching intermittent fasting for 25 years and following it himself since the 1980s, said in an interview.

Fasting 16 hours, from the end of dinnertime to late morning the next day, “is enough to trigger changes in the brain and body, studies suggest,” Mattson said, although it may take the body several weeks to adjust to the new way of eating. And by the way, if you’re caffeine-dependent, having unsweetened coffee or tea in the morning instead of an early breakfast won’t break the fast.

For those who can’t skip breakfast in the morning, Lauri Wright, a spokesperson for the Florida Academy of Nutrition and Dietetics and chair of the department of nutrition and dietetics at the University of North Florida, suggests narrowing the fasting window to eight to 12 hours, with “the bulk of the fast occurring while you sleep,” she said in an email.

The idea, says Mattson, “particularly in people who are overweight, is to use intermittent fasting to change their eating pattern, which may help them keep their weight within healthier limits and also have some cognitive benefits. Exercise and keeping intellectually engaged is also important.”

Mattson and coauthor Rafael de Cabo of the National Institute on Aging, published a paper in December 2019 in the New England Journal of Medicine that reviewed the current state of intermittent fasting research in both animals and humans.

They wrote that studies and clinical trials show that “intermittent fasting has broad-spectrum benefits for many health conditions, such as obesity, diabetes mellitus, cardiovascular disease, cancers and neurologic disorders.”

Animal studies, which make up the bulk of intermittent fasting research, suggest that intermittent fasting improves an animal’s health throughout its life span. Human studies, however, have mainly looked at fasting’s effects over several months, so “it remains to be determined whether people can maintain intermittent fasting for years.” And results of research in animals doesn’t always translate to the same results for research in humans.

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It’s not for everyone. Dietitian Lauri Wright admits she’s not a huge fan of intermittent fasting. Some of her older clients have tried it, but have found it hard to stick with. She worries that “fasting can make some people feel lightheaded or dizzy, which could increase the risk of a fall. I also worry about seniors getting adequate nutrients while intermittent fasting, especially protein.”

Talk to your health provider first. “Anyone considering intermittent fasting should first discuss it with a doctor, especially if they’re taking medications that may need to be adjusted, have a chronic disease or a history of eating disorders or disordered eating,” Wright advises. A better idea may be working with a registered dietitian who can individualize a meal plan to fit your needs and goals.

Learn more about the research in this article

• “Clinical application of intermittent fasting for weight loss: progress and future directions,” Nature Reviews Endocrinology, February 2022. In this review, researchers analyze multiple studies to investigate the health benefits of intermittent fasting. Results showed that weight loss achieved through intermittent fasting was equivalent to weight loss achieved through traditional dieting. Additionally, some studies showed intermittent fasting lowered blood pressure, improved cholesterol and improved insulin resistance. Read a summary of the study. (A fee is required to access the full study.)

• “Intermittent Fasting and Metabolic Health,” Nutrients, January 2022. In this review, 66 studies were reviewed to analyze the effects of intermittent fasting on the major components of metabolic syndrome. Researchers found that intermittent fasting had positive effects on weight loss and insulin resistance. Additionally, intermittent fasting was shown to have benefits for hypertension and improving cardiovascular risk factors. Read the full study.

• “Effects of Intermittent Fasting in Human Compared to a Non-intervention Diet and Caloric Restriction: A Meta-Analysis of Randomized Controlled Trials,” Frontiers in Nutrition, May 2022. In this review, 43 randomized controlled trials were reviewed to investigate the effects of intermittent fasting compared to non-intervention diets or caloric restriction diets. Researchers found that intermittent fasting improved weight loss, insulin resistance and cholesterol compared with non-intervention diets. Read the full study.

• “Daytime eating prevents internal circadian misalignment and glucose intolerance in night work,” Science Advances, December 2021. In this study, 19 healthy adults (average age of 26.5) underwent 14 days of simulated night work. Researchers randomly assigned participants to consume their meals during the day and night or to consume their meals only during the day. Results showed that participants under night work simulation who ate during both daytime and nighttime experienced impaired glucose tolerance. Participants under night work simulation who consumed all their meals during the daytime did not experience glucose intolerance. Read the full study.

• “Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity,” Cell Metabolism, October 2022. In this study, researchers investigated the effect of late eating on hunger, appetite and energy expenditure while controlling for nutrient intake, physical activity, sleep and light exposure. Results showed that late eating increased hunger, altered appetite and decreased energy expenditure leading to an increased risk of obesity. Read a summary of the study. (A fee is required to access the full study.)

• “Effects of Intermittent Fasting on Health, Aging, and Disease,” The New England Journal of Medicine, December 2019. Researchers reviewed multiple animal and human studies to explore the health effects of intermittent fasting. Evidence suggests that intermittent fasting may have a wide range of benefits for several health conditions, including diabetes, obesity and cardiovascular disease. Read a summary of the study. (A fee is required to access the full study.)

• “Intermittent Fasting Enhanced the Cognitive Function in Older Adults with Mild Cognitive Impairment by Inducing Biochemical and Metabolic changes: A 3-Year Progressive Study,” Nutrients, August 2020. In this study, researchers compared the cognitive functioning of 99 older adults (age 60 and up) with mild cognitive impairment. Participants were either regularly practicing intermittent fasting, irregularly practicing intermittent fasting or were not fasting at all. After 36 months, those who regularly practiced intermittent fasting had better cognitive scores and improved cognitive functioning compared with those who fasted irregularly and those who did not fast at all. Read the full study.