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Why does eating late lead to obesity and diabetes?

Scientists have long investigated the connection between meal timing, sleep, and obesity, arguing that overnutrition could disrupt circadian rhythms and change fat tissues. However, the mechanism behind why eating late at night is linked to weight gain and health issues such as diabetes is still poorly understood.

Now, a team of scientists from the Northwestern University has found that energy release may be the molecular mechanism through which our internal clocks control energy balance – an aspect which suggests that, for humans, daytime is the ideal time in the light environment of the Earth’s rotation when it is optimal to dissipate energy as heat. These finding could have a range of implications, from dieting and sleep loss to how clinicians feed patients who require long-term nutritional assistance.

“It is well known, albeit poorly understood, that insults to the body clock are going to be insults to metabolism,” said study corresponding author Joseph T. Bass, a professor of Medicine at Northwestern. “When animals consume Western style cafeteria diets — high fat, high carb — the clock gets scrambled. 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.”

In this recent study, the scientists focused on mice, which are nocturnal animals. By feeding them a high-fat diet either exclusively during their inactive or active period – while setting the lab temperature to 30 degrees, at which mice expand less energy, to mitigate the effects of temperature on their findings – the researchers discovered that those fed during light hours gained more weight compared to those fed in the dark.

“We thought maybe there’s a component of energy balance where mice are expending more energy eating at specific times,” said study first author Chelsea Hepler, a postdoctoral fellow in Professor 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.” 

These findings could inform chronic care, particularly in cases where patients have gastric feeding tubes. Such patients are commonly fed at night while they sleep and they are releasing the least amount of energy. Since many of them tend to develop obesity and diabetes, medical professional should re-think their strategy to improve their patients’ health and well-being.

The study is published in the journal Science.

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By Andrei Ionescu, Staff Writer

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