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Working late-night shifts or eating at the wrong time can increase the risk of metabolic syndrome, obesity, and diabetes.

New research from Vanderbilt University explains why it matters not only what you eat, but also when you eat it. Insulin action rises and falls according to a 24-hour, circadian rhythm, the researchers team led by Carl Johnson, Ph.D. found. What's more, mice unable to keep the time for one reason or another get stuck in an insulin-resistant and obesity-prone mode.
Insulin, which is made in the pancreas, plays a key role in regulating the body's fat and carbohydrate metabolism. When we eat, our digestion breaks down the carbohydrates in our food into the simple sugar glucose, which is absorbed into the blood stream.

Too much glucose in the blood is toxic, so one of insulin's roles is to stimulate transfer of glucose into our cells, thereby removing excess glucose from the blood. Specifically, insulin is required to move glucose into liver, muscle and fat cells. It also blocks the process of burning fat for energy.

Insulin action - the hormone's ability to remove glucose from the blood - can be reduced by a number of factors and is termed insulin resistance. The study found that normal "wild-type" mouse tissues are relatively resistant to insulin during the inactive/fasting phase whereas they become more sensitive to insulin (therefore better able to transfer glucose out of the blood) during the high activity/feeding phase of their 24-hour cycle. As a result, glucose is converted primarily into fat during the inactive phase and used for energy and to other tissue building during the high activity phase.
According to Research News at Vanderbilt

Professor Johnson's team took careful measurements of insulin in mice at different hours to reveal a regular pattern. Normal mice become insulin resistant during the day, when the nocturnal animals are mostly sleeping.

But mice unable to keep the time based on a genetic defect or constant exposure to light lost that rhythm. They also gained more weight when fed on high-fat mouse chow.

And so it is that insulin action and blood sugar metabolism are tied to the time of day and to the internal mechanisms that keep track of that time.

That's why Professor Johnson says it is probably best to eat a light supper and avoid snacking after dinner.

Reference

Current Biology, Shi et al.: "Circadian disruption leads to insulin resistance and obesity."