Scientists discover why late-night eating promotes weight gain, diabetes

EVANSTON, Ill. — The occasional midnight snack can be a tasty change of pace, but doctors and nutritionists agree late-night eating isn’t a healthy habit on a regular basis. Now, researchers from Northwestern University may have uncovered why evening eating often leads to weight gain and diabetes.

The intricate relationship between when we eat, when we sleep, and obesity risk is a generally well-known but poorly understood health topic. Prior research, however, does suggest over-nutrition can disrupt circadian rhythms and change fat tissue. This latest work details, for the first time ever, that releasing energy may be the molecular catalyst through which our bodily internal clocks control energy balance.

Additionally, study authors report eating in the daytime appears to be the most ideal or optimal time — in the light environment of the Earth’s rotation to dissipate energy as heat. They explain that these discoveries hold broad implications across various health topics such as dieting, sleep loss, and the best way to feed patients requiring long-term nutritional assistance.

“It is well known, albeit poorly understood, that insults to the body clock are going to be insults to metabolism,” says corresponding study author and endocrinologist Dr. Joseph T. Bass, the Charles F. Kettering Professor of Medicine at the Feinberg School of Medicine, in a university release.

“When animals consume Western style cafeteria diets — high fat, high carb — the clock gets scrambled,” Bass adds. “The clock is sensitive to the time people eat, especially in fat tissue, and that sensitivity is thrown off by high-fat diets. We still don’t understand why that is, but what we do know is that as animals become obese, they start to eat more when they should be asleep. This research shows why that matters.”

Releasing heat helps the body avoid weight gain

During the study, mice (nocturnal animals) were given a high-fat diet either exclusively during their inactive (light) period or during their active (dark) period. Within just a week, the mice fed during light hours showed notably more weight gain than those fed in the dark. Study authors were also sure to set the temperature to 30 degrees, which is the temperature at which mice expend the least energy. This was done to mitigate the effects of temperature on their findings.

“We thought maybe there’s a component of energy balance where mice are expending more energy eating at specific times,” explains first study author Chelsea Hepler, a postdoctoral fellow in the Bass Lab. “That’s why they can eat the same amount of food at different times of the day and be healthier when they eat during active periods versus when they should be sleeping.”

The observed increase in energy expenditure inspired researchers to analyze the metabolism of fat tissue in an effort to see if the same effects took place within the endocrine organ. The same effects were in fact observed, and mice with genetically enhanced thermogenesis, or heat release through fat cells, didn’t gain weight and showed improved health.

Dr. Hepler also discovered futile creatine cycling within fat tissues, which describes the process by which creatine (a molecule that helps maintain energy) undergoes storage and release of chemical energy. This discovery strongly suggests creatine could be the mechanism underlying heat release.

This could change how hospitals feed patients

The scientific groundwork for these findings was actually put in place over 20 years ago by research performed by Dr. Bass and colleagues at Northwestern. Back then, researchers found a relationship between the internal molecular clock and body weight, obesity, and metabolism in animals. Since then, the big challenge for Bass’s lab has been determining what it all means and identifying the control mechanisms underlying the relationship. This latest work represents a major step forward.

Dr. Bass explains this study could better inform chronic care, especially cases in which patients must use a gastric feeding tube. In such scenarios, patients are typically fed through a tube in the evening while the sleep – which is when they’re releasing the least amount of energy. Rates of diabetes and obesity tend to be higher among patients using gastric feeding tubes, and this study may finally explain why.

Dr. Bass also wonders how this research may impact Type 2 diabetes treatments. For instance, should mealtimes be considered when insulin is given?

“We need to figure out how, mechanistically, the circadian clock controls creatine metabolism so that we can figure out how to boost it,” Dr. Hepler concludes. “Clocks are doing a lot to metabolic health at the level of fat tissue, and we don’t know how much yet.”

The study is published in the journal Science.

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