Snacking nonstop during the summer? If you’re a boy, blame the sun! Two human and mouse investigations by international researchers found that exposure to sunshine increased food intake and weight gain in males but had no effect on females.

Sunlight exposure boosts food intake and weight gain in males, but not in females, via a hormone released by skin fat cells.

The research, which was published in Nature Metabolism, sheds light on a process that has largely gone unnoticed: how sunshine may impact eating habits and overall energy balance.

The brain and peripheral tissues communicate to a large extent in order to regulate the urge to eat. Several organs, including the liver, adipose tissue, and the gastrointestinal tract, release hormones that then travel to specific brain areas, including the hypothalamus, which determines whether or not eating is necessary based on the body’s current energy needs.

Carmit Levy and colleagues examined epidemiological data from almost 3,000 people in Israel over the course of three years, and they found that men, but not women, increased their food intake during the summer, when sun radiation is at its highest.

Studies on male mice showed that daily exposure to ultraviolet (UVB) radiation for ten weeks caused the release of the hunger hormone ghrelin from the skin’s fat tissue, supporting the conclusion.

These male mice’s ghrelin enhanced appetite once it reached the hypothalamus, encouraging food consumption and weight gain.

However, in female mice, this impact was diminished because the sex hormone estrogen inhibited the release of ghrelin from fat cells in the skin.

Additionally, male human skin samples exposed to UVB over a five-day period in an experimental setting resulted in increased ghrelin expression, which is consistent with the increased food-seeking behavior seen following solar exposure.

The study’s findings, according to the authors, suggest that skin fat may act as a mediator of feeding behavior by influencing exposure to sunlight, possibly introducing a new subtype of fat tissue into the energy balance equation.

Carlos Dieguez and Ruben Nogueiras write in a related News & Views article that this work will surely pave the way for further studies on the role of the skin in energy and metabolic homeostasis”.

Image Credit: Getty

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