Eat and Work Earlier in the Day for Better Glucose Tolerance

September 24, 2015 Brigham and Women's Hospital

Eating late at night and working overnight both increase the risk of developing type 2 diabetes.

A new research study by Brigham and Women’s Hospital (BWH) suggests that it’s not only what we eat that impacts our health, but when we eat.

According to the research, eating later in the day lowers the body’s ability to regulate blood sugar levels, also known as low glucose tolerance.  The study, published in Proceedings of the National Academy of Sciences in March 2015, also found that night shift workers who sleep during the day and work overnight had lower glucose tolerance than those who are awake during the day and sleep at night. This, in turn, can impact health issues like weight gain, insulin resistance, and risk for developing type 2 diabetes.

The study compared circadian rhythms, sleep/wake cycles, and mealtime to blood glucose levels in 14 healthy participants. All subjects participated in two protocols. In one protocol, the individuals were awake during the day, had their first meal at 8 a.m., their last meal at 8 p.m., and slept at night. In the second, they slept during the day, had their first meal at 8 p.m., stayed up all night, and had their last meal at 8 a.m.

They discovered two interesting things. Compared to eating earlier in the day, eating later in the day at 8 p.m. led to lower glucose tolerance (higher blood sugar), regardless of their sleep cycle times. Second, compared to sleeping at night, sleeping during the day and staying awake all night disrupts the body’s circadian system, which, in turn, decreases insulin sensitivity. Just one shift of night work can cause a circadian misalignment that lowers glucose tolerance throughout multiple days.

The circadian system, which is the body’s internal clock, regulates important daily functions, like the sleep/wake cycle and metabolism. Working night shifts has been proven to disrupt the circadian system. Disruptions in the circadian system are associated with decreased insulin sensitivity, which results in increased blood sugar levels and elevated risk for type 2 diabetes. This can explain why night shift workers are at increased risk of type 2 diabetes.

Though the study included all races, another study at the Slone Epidemiology Center at Boston University discovered that non-Hispanic blacks who worked night shifts, especially for longer duration, had a significantly higher risk for type 2 diabetes. Those who worked night shifts for one to two years had a 17 percent increased risk for type 2 diabetes; those who worked three to nine years had a 23 percent higher risk; and those worked more than 10  years had a 42 percent increased risk.

What does this mean? Avoid late-night snacking and try eating your meals – especially dinner – before 8 p.m. Researchers at the BWH Division of Sleep and Circadian Disorders are working on strategies to help night shift workers reduce their risk for type 2 diabetes. “Because night work will never disappear, we’re investigating whether it’s possible to schedule food intake to occur at more advantageous times,” says Frank A. J. L. Scheer, PhD, Director of the Medical Chronobiology Program at BWH.

These discoveries have significant public health implications, especially for those who have other risk factors for type 2 diabetes.

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- Skylar M.

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