Those who hope to lose some weight in time for Christmas should be keeping an eye on when they eat, not just what they eat, according to scientists.
In a study focused on time-restricted diet and the effects on diabetes and obesity, researchers found that confining meals to a 12-hour window made a huge difference to whether fat is stored or burned up by the body.
In other words, eating during the day and fasting after dark could be the best way forward for weight loss.
Scientists at The Salk Institute in the US evaluated different diet types and eating patterns on 392 mice with varying degrees of obesity.
They found that those with restricted eating hours were less likely to gain weight and were generally healthier and slimmer than those who were allowed access to the same amount of food for the whole day.
This was despite the fact that all of the mice were on a high fat diet and consumed the same amount of calories per day.
"It's not just what we eat, but when we eat," says Professor Satchidananda Panda who led the study. "If we let mice eat for only 8-9 hours a day, those mice are protected from weight gain, diabetes and obesity."
The researchers gave some of the time-restricted mice a respite on weekends, allowing them free access to high-fat meals for these two days.
These mice had less fat mass and gained less weight than the mice given a freely available, high-fat diet the whole time.
In fact, the mice that were freely fed just on weekends looked much the same as mice given access to food 9 or 12 hours a day for seven days a week, suggesting that the diet can withstand some temporary interruptions.
Rejoice! The odd takeaway on a Saturday night is allowed.
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“The fact that it worked no matter what the diet, and the fact that it worked over the weekend and weekdays, was a very nice surprise,” says the study’s first author Amandine Chaix, a postdoctoral researcher in Professor Panda’s lab.
More importantly, for the mice that had already become obese by eating a freely available high-fat diet, researchers restricted their food access to a nine-hour window.
Although the mice continued to consume the same number of calories, they dropped body weight by five percent within a few days.
Importantly, eating this way prevented the mice from further weight gain (by about 25% by the end of the 38-week study) compared to the group kept on the freely available high-fat diet.
"We were also surprised to find that the obese mice lost bodyweight, reduced their blood sugar levels and had lower cholesterol," says Professor Panda.
The study is published in the Cell Metabolism journal.
Moral of the story: keep an eye on the clock, not just the calories.