DALLAS — Eating primarily during the day instead of at night could be the key to a longer life, new research reveals. Researchers from the University of Texas Southwestern Medical Center say it’s not just what you consume, but when.
Their study finds that cutting down on fatty and sugary foods and having meals at the right time increased the longevity of mice by 35 percent. Experiments found the body clock’s daily rhythms play a big part in the benefits of a healthy diet. Rodents are nocturnal animals that are most active in the dark. Meanwhile, humans are generally livelier during the day. With that in mind, study authors say people should restrict their dining to the most active hours of the day.
In lab animals tracked over four years, a reduced-calorie diet alone extended survival by 10 percent. However, the improvement increased significantly with an exclusive nighttime feeding schedule. The combination tacked on an extra nine months to their typical two-year average lifespan.
Lead author Professor Joseph Takahashi says a similar plan for people would restrict eating to the daytime hours. Eating less is known to boost health. Studies on a variety of animals have shown it can lead to a longer, healthier life. The latest findings add to the evidence that having a hearty breakfast or lunch instead of dinner is also key — at least for humans.
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Prof. Takahashi, a molecular biologist, adds that their research helps untangle the controversy surrounding diet plans that emphasize eating only at certain times of day — which many people refer to as intermittent fasting. Although these plans may not speed weight loss in humans — according to a recent study in the New England Journal of Medicine — they can lead to other health benefits which increase the average lifespan.
Intermittent fasting diets have become increasingly popular in recent years. They include fasting on alternate days or eating only during a period of six to eight hours per day. Now, Prof. Takahashi and his colleagues have unraveled the effects of calories, fasting, and circadian rhythms on longevity. They housed hundreds of mice with automated feeders to control when and how much each animal ate for its entire lifespan.
Some could gorge as much as they wanted while others had their calories restricted by 30 to 40 percent. The latter group also ate on different schedules. Mice fed the low-calorie diet at night, over either a two-hour or 12-hour period, lived the longest.
The results suggest time-restricted eating has positive effects on the body even if it doesn’t promote weight loss. The study also found no differences in body weight among mice on different eating schedules. “However, we found profound differences in lifespan,” Prof. Takahashi notes in a media release.
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The team hopes that learning how calorie restriction affects the body’s internal clocks as we age will help scientists find new ways to extend healthy lifespan. That could come through calorie-restricted diets or through drugs that mimic the effects of those diets.
Meanwhile, Prof. Takahashi is taking a lesson from his mice, restricting his own eating to a 12-hour period. “If we find a drug that can boost your clock, we can then test that in the laboratory and see if that extends lifespan.”
Rafael de Cabo, a gerontology researcher at the National Institute on Aging in Baltimore, says the new paper “is a very elegant demonstration that even if you are restricting your calories but you are not [eating at the right times], you do not get the full benefits of caloric restriction.”
Nutritionist Dr. Sai Krupa Das of Tufts University, who did not take part in the study, adds that the results highlight the crucial role of metabolism in aging. “This is a very promising and landmark study,” Dr. Sai Das says.
Decades of research has found calorie restriction extends the lifespan of animals ranging from worms and flies to mice, rats, and primates. Those experiments report weight loss, improved glucose regulation, lower blood pressure, and reduced inflammation.
However, it’s been difficult to systematically study calorie restriction in people who can’t live in a laboratory and eat measured food portions for their entire lives. Dr. Sai Das helped conduct the first controlled study in humans called CALERIE (Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy).
It found even a modest reduction “was remarkably beneficial” for reducing signs of aging. Scientists are just beginning to understand how calorie restriction slows aging at the cellular and genetic level. As an animal ages, genes linked to inflammation tend to become more active while those that regulate metabolism slow up.
Prof. Takahashi discovered calorie restriction, especially when timed to the mice’s active period at night, helped offset these genetic changes as they got older.
The findings appear in the journal Science.
South West News Service writer Mark Waghorn contributed to this report.