DIETING
December 4, 2014

The Case Against Midnight Snacks

When you eat may be just as important as what you eat. Eating on a schedule makes the body's metabolism run more efficiently.

When do you eat your last meal of the day? Back in 2012, a team of researchers found that most of the health problems mice get from eating a high-fat diet could be eliminated if they only ate during an eight-hour period. Mice given all-day access to the same food consumed the same number of calories but were much fatter and in poorer health.

This wasn't just a statistical difference. It was clearly visible. Mice with all-day access were considerably fatter.

Now researchers from the same lab have found that restricting the time of day when you eat has the potential to offer additional and substantial health benefits. When you eat can even reverse obesity and diabetes, at least in mice.

When obese mice who had been eating a high-fat diet with 24-hour food access were switched to a nine-hour meal day, they immediately began dropping weight.

The finding suggests a whole new strategy to all who've dieted without success — the idea that when you eat is as important as what you eat.

In the current study, over 400 mice were given various different diets and time restrictions as to when they could eat them. The benefits of a time-restricted diet showed up no matter what the initial weight of a mouse was or what type diet it was eating, though some combinations gave a stronger effect than others.

One of the first findings was that eating time didn't have to be restricted to eight hours. A high-fat diet eaten over nine, ten- or even 12-hour periods all resulted in similarly lean mice. But when the eating period was extended to 15 hours, the benefits were much more modest. This pattern was also seen if the mice ate a high-sugar diet.

Perhaps more importantly, when obese mice who had been eating a high-fat diet with 24-hour food access were switched to a nine-hour meal day, they immediately began dropping weight, losing 5% of their total weight in just a few days.

Maintaining this regimen — still eating the same diet and number of calories that had made them fat — prevented the mice from gaining any more weight over the course of the 38-week study, while mice eating the same diet over a full 24 hours continued to gain weight throughout the study.

Even when time-restricted mice were allowed 24-hour access to food only on weekends, benefits were pretty much the same, suggesting that the routine allows some flexibility.

For mice given a more balanced diet, those who were time-restricted had more lean muscle mass than their eat-all-day littermates. In other words, time restriction offers benefits even to those who have been eating right and are normal weight.

These effects all seem to be linked to the body's biological clock. Eating on a schedule appears to synchronize hundreds of genes and gene products. The synchronization makes the body's metabolism run more efficiently.

Of course, laboratory mice aren't people. Trials in humans are needed to confirm whether this approach will work. But for anyone who has ever struggled with a weight problem or been frustrated by unsuccessful dieting, the study offers another option that's easy to try out, if you can just keep in check those midnight cravings.

The study is published in Cell Metabolism.

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