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That pre-bedtime snack may be doing more harm than you imagine – even if it’s healthy

A new study by researchers at the Salk Institute for Biologic Studies suggests that confining kilojoule consumption to an eight-to-12 hour period – as past generations did – might stave off high cholesterol, diabetes and obesity.

The results, published in Cell Metabolism, add to mounting evidence suggesting that when we eat matters as much to our health as what we eat.

In 2012, Salk Institute associate professor Satchidananda Panda showed that mice fed a high-fat diet, which they could access for just eight hours a day, were healthier and slimmer than mice given 24-hour access to the same food. This despite the two groups consuming the same number of kilojoules.

This latest study reveals the benefits of time restriction are more profound than initially believed, and that in animal models it can actually reverse obesity and diabetes. The authors demonstrated that time restriction better synchronises the function of hundreds of genes and gene products in the body with the predictable time of eating.

These days, most of the advice is… ‘you have to eat a healthy diet’, ” says Panda. “But many people don’t have access to healthy diets. So the question is, without [such] access, can they still practise time-restricted feeding and reap some benefit?”

To determine just how forgiving time-restricted feeding is, Panda and his team fed almost 400 mice, ranging from normal to obese, various types of diets with differing length-of-time restrictions. They found the benefits of time-restricted feeding showed up regardless of the mouse’s weight, type of diet and length of the time restriction (to some degree).

Image: Courtesy of the Salk Institute for Biological Studies

  • Mice whose diets were restricted within a time frame developed less body fat.
  • Large fat droplets (white, left panel) accumulated in brown adipose tissue of mice freely fed a high-fat diet.
  • The tissue of mice fed the same diet in a nine-hour time window (right) was less fat-filled.
  • Regardless of whether their diets were high in fat, fat and sucrose, or just fructose, mice that were given time restrictions of nine to 12 hours, and consumed the same amount of daily kilojoules as their unrestricted counterparts, gained less weight than the controls.
  • Variations in the time window in which the mice were allowed to eat a high-fat diet – including nine, 10 and 12-hour periods – all resulted in similarly lean mice. However, for a 15-hour group, the benefits conferred by time restriction became more modest.
  • Some of the time-restricted mice were given a respite on weekends, allowing them free access to high-fat meals for the 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, mice that were freely fed just on weekends looked much the same as mice given access to food nine or 12 hours a day for seven days a week, suggesting this diet can withstand some temporary interruptions.
  • Researchers restricted the food access of mice that had already become obese by eating a freely available high-fat diet over a nine-hour period. Although they continued to consume the same number of kilojoules, their body weight dropped by five percent within a few days. And importantly, eating this way prevented the mice from further weight gain – by about 25 percent by the end of the 38-week study – compared to the group kept on the freely available high-fat diet.
  • When the group compared mice given a more balanced diet, they found the time-restricted mice had more lean muscle mass than the unfettered group.
  • A comprehensive analysis of the blood metabolites in time-restricted mice revealed that multiple molecular pathways that go awry in metabolic disease are turned back to normal, and protective pathways are dialed up.

“It’s an interesting observation that although the mice on a normal diet did not lose weight, they changed their body composition,” Panda comments. “That brings up the question: what happens? Are these mice maintaining muscle mass that might have been lost with free feeding, or are they gaining muscle mass?”

Next steps include looking more in-depth at these molecular pathways, as well as investigating the effects of time-restricted eating in humans.

Written for the Australian Traditional-Medicine Society (ATMS) by Rosemary An Ogilvie from materials released by the Salk Institute for Biological Studies

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