For healthy eating, timing matters

Limiting mealtimes to a 12-hour period per day helps fruit flies’ hearts

fruit fly heartbeat graph

KEEPING TIME  Fruit flies that eat just 12 hours per day (blue lines) maintain steady heartbeats into middle age (5 weeks old), while the hearts of flies that can eat around the clock (red) beat irregularly. Each red or blue dash represents the contraction of the heart.

S. Gill et al/Science 2015

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When you eat may determine how long and strong your heart beats.

Fruit flies that limited eating to 12-hour stints had steadier heartbeats in old age than flies that ate whenever they wanted, researchers report in the March 13 Science. The study adds to a growing body of evidence that the timing of meals may be as important for health as diet composition and calorie counts are.

The research also “suggests that the body clock is involved in cardiovascular function and risk,” says Frank Scheer, a neuroscientist and physiologist at Brigham and Women’s Hospital in Boston and Harvard Medical School. Scheer was not involved in the fruit fly study, but has shown that disrupting people’s daily, or circadian, rhythms can damage their health.

Circadian clocks work in nearly every cell in the body. They govern a wide variety of body rhythms, such as those associated with body temperature, blood pressure and sleep. The main timekeeper is located in the brain and is set by light, but other clocks synchronize themselves according to feeding time (SN: 4 /10/10, p. 22).

Previous research in mice has suggested that limiting eating to 12 hours per day could protect rodents from obesity and other ravages of high-fat diets. Those studies couldn’t address heart problems associated with poor diet because mice don’t get heart disease the way humans do, says Satchidananda Panda, a circadian biologist at the Salk Institute for Biological Studies in La Jolla, Calif. Fruit flies, on the other hand, develop irregular heartbeats and other heart problems as they age. So Panda and his colleagues set out to test whether limiting the amount of time fruit flies eat, but not cutting back on calories, could affect the insect’s heart health.

One group of flies ate around the clock; the other had access to their cornmeal diet for 12 hours each day. Both groups ate about the same amount overall, but the 24-hour group snacked at night. 

Both groups of flies had similar amounts of activity. The limited-timed feeding flies did most of their moving during the day, though. They also slept better at night.

At 3 weeks old, both groups of flies had regular, healthy hearts. At 5 weeks, the 12-hour eaters’ hearts maintained a steady rhythm of roughly one beat per second. The hearts of the anytime eaters beat irregularly, sometimes skipping a beat and sometimes quivering. By 7 weeks, the anytimers had badly deteriorated heart function. Flies on a 12-hour schedule also lost a few beats, but their heart problems were not as severe.

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IN A HEARTBEAT   The hearts of middle-aged fruit flies beat erratically if the insects are allowed to eat whenever they want (top). But flies of the same age that eat for only 12 hours per day (bottom) still have strong, steady hearts, even though they consume the same amount of food.

Gill et al./Science 2015

Switching anytime flies to a 12-hour schedule at 5 weeks old — fruit fly middle age — improved some measures of heart function, but not all. In other experiments, restricting feeding time also staved off some of the negative heart effects of high-fat diets.

When researchers disabled circadian clocks throughout some fruit flies’ bodies, restricting eating times didn’t help those flies’ hearts, suggesting that functioning clocks are important for heart health.

Researchers also looked at timed eating’s impact on gene activity. Many genes follow circadian rhythms, peaking in activity during certain times of day. In fruit flies with curtailed eating schedules, those peaks crescendoed right before breakfast and just before the last mouthful. Anytime eaters had several smaller peaks throughout the day. That finding suggests that timed feeding improves coordination of gene activity.

Panda likens the effect to getting a tune-up on a car. “The spark plugs need to fire in sequence,” he says. “If you just fire randomly, you’ll have a big problem and the head gasket will blow up.” Similarly, tightly controlling gene activity may allow for more efficient energy usage and prevent metabolic by-products from building up and damaging tissues, he says.

Improved sleep in the 12-hour eaters might account for some of the heart benefits, Scheer says. Lack of sleep is linked to a variety of diseases in people, including heart disease (SN: 10/24/09, p. 28). No one knows whether restricting mealtimes will improve human health, he says. “I don’t think there’s evidence that it’s bad, but there’s too little evidence for me to recommend it.”

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