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It's Not Just What You Eat — It's When You Eat

Can following your body's natural rhythms help you lose weight?

By Steven N. Austad

(Editor’s note: This article is part of an editorial partnership between Next Avenue and The American Federation for Aging Research, a national nonprofit organization whose mission is to support and advance healthy aging through biomedical research.)

When You Eat
Credit: Adobe Stock

Eating less improves health. We have all heard this — and scientists have known this — for decades. From portion control to calorie counting, recommendations on nutrition and dietary choices often focus on limiting our intake of what we eat daily. But new research suggests that when it comes to healthy eating for healthy aging, it’s not just what you eat or how much you eat, but when.

The first evidence of the impact of dietary timing has been seen in mice studies. Mice are the standard laboratory mammals from which we learn much of what we know about human biology.

In a typical mouse study to explore how reducing calories can improve health, the control group of mice always has food available. This group nibbles throughout the 24-hour day. The other “dietary restriction” group typically gets about 60-70 percent of the amount of food the control group eats. Because they are always hungry, mice on this restricted diet gobble their daily food allotment almost immediately when it arrives. They don’t get another meal for more than 23 hours, which means that they “fast” for more than 23 hours. For years in studies, researchers have observed that these dieting mice show numerous signs of improved health and resilience and have attributed those effects to reduced calories. Now, it turns out the 23-hour fast may be as important as the reduced calories.

One of the known benefits of mouse dietary restriction is that they recover faster and more completely from surgery than fully-fed mice. However, mice who fasted for two days prior to surgery recovered just as well as mice fed a restricted diet for a month. Mice who fasted for only two days are also much more resistant to the toxic side effects of drugs, such as those commonly used in cancer chemotherapy.

As a result, clinical trials are now ongoing to see if fasting hastens recovery from surgery and reduces side-effects of chemotherapy in people, too.

Do Fasts and Timed Diets Work for Humans?

Led by researchers supported by The American Federation for Aging Research (AFAR), discoveries about the advantages of short-term, periodic fasts in mice have led to a number of fasting-based diets that are now being tested for their health-enhancing effects in humans.

One approach is the “fasting-mimicking diet” developed by AFAR expert Valter Longo, who is the director of the Longevity Institute at the University of Southern California. Longo’s approach starts at the cellular level. The cells of our bodies are exquisitely sensitive to the food we eat. We have nutrient sensors in all of our cells that turn on or off hundreds of genes when they are triggered by food. Nutrients in food can be better or worse at triggering those sensors.

As explored in his book The Longevity Diet, Longo has developed diets that avoid triggering these nutrient sensors, which is why they are "fasting-mimicking.” These diets have shown some remarkable effects on reversing diabetes in mice. As with various other fasting regimes, studies are underway to assess possible health benefits in people.


Another body of dietary recommendations builds on research on the timing of what we eat relative to our natural body rhythms. Virtually every living creature undergoes daily body rhythms dependent on the day-night, light-dark cycles. Hormones are secreted at certain times of the day, our immune system is more active at certain times compared to others, our blood pressure, digestive system and our body’s ability to repair itself, all have daily or circadian cycles.

Follow Your Circadian Rhythms

Satchin Panda of the Salk Institute has studied these rhythms for years and has concluded, among other things, that one pathway to good health is by timing our meals in alignment with our daily body rhythms.

In his new book, The Circadian Code, Panda documents that most people eat over a 15-hour or longer time period each day, almost like mice with unlimited food. The most healthful way to eat, he suggests, is to have all your meals within an eight-to-10-hour period, stretching from early morning to early evening.

Notice that by doing this, you are actually fasting 14 to 16 hours each day. So this “time-restricted feeding” has elements of fasting associated with it.

Research, again with mice, has shown that eating in this time restricted fashion improves health, even when the mice are eating an unhealthy fat-and-sugar laden diet. Several short-term human studies with this dietary approach have found it to be an excellent way to control weight, but it also seems to have health benefits beyond its impact on weight. Panda’s lab has even developed an app that helps you better understand your body’s rhythms.

Join Valter Longo, Satchin Panda and Steven Austad for a free webinar on Thursday September 27: It’s Not Just What You Eat, But When. These experts will present their research on fasting-mimicking diets, caloric restriction and the Circadian code and answer your questions. Learn more and RSVP here.

Steven N. Austad, Ph.D., is the senior scientific director of the American Federation for Aging Research, the co-principal investigator of the National Institute of Aging’s Nathan Shock Centers of Excellence Coordinating Center, and a distinguished professor and department chair in the Department of Biology at the University of Alabama at Birmingham. He is author of more than 190 scientific articles and more than 100 newspaper columns on science. Follow him on Twitter @StevenAustad. Read More
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