The weight of summer hibernation

The calendar may say October, but the temperature still screams it's oppressively hot outside. That could explain why food ranks low on the priority list. Here's the kicker: Your waistline may still be expanding.

Pennington Biomedical Research Center scientists have found a brain mechanism that connects warm temperatures to appetite and calorie burning. Heat makes you eat less, but it makes you burn even less.

Why it matters: Weight isn't only about diet and exercise. Temperature may play a role too, and most of us hunker down in air conditioning through the hot months.

Details matter: The study, published in Communications Biology, focused on the hypothalamus. That region of the brain regulates body temperature and energy balance. Researchers identified a group of neurons that respond to warmth.

In animal models, warm temperatures activated those neurons. Hunger dropped and fullness rose. But energy expenditure fell by more than food intake did. Over time, the result was weight gain.

Researchers call that an "obesogenic" effect of warm environments.

The Big Picture: The team stops short of blaming the thermostat. Heike Muenzberg-Gruening, director of Pennington's Central Leptin Signaling Laboratory, said modern, temperature-controlled environments "may contribute to obesity in ways we are only beginning to understand."

The researchers say the work could eventually inform new obesity treatments that target these brain pathways.

The Bottom Line: This is early, animal-based research. It does not show that air conditioning makes people gain weight, and nobody is suggesting you turn it off. But it is a reminder that the brain weighs more than calories in and calories out.