It is generally accepted that in the heat the appetite is not as strong as in the cold winter months. So, this is a misconception, at least in relation to men, scientists from Tel Aviv University found out. In an article published in the journal Nature Metabolism, they write that men consume more calories in the summer than at any other time of the year, because sunlight, hitting the skin, increases the secretion of an appetite-enhancing hormone. Women are not affected, NewScientist reports.
The researchers noticed this effect in lab mice they were experimenting with while studying the mechanisms behind skin cancer: the males ate more when they were exposed to ultraviolet light. To test whether this is true in humans, the researchers used data from 3,000 people who completed diet questionnaires as part of the regular National Health Survey. It turned out that from March to September, men consumed about 17% more calories than in the rest of the year. In women, this pattern was not observed.
Appetite is a product of many body systems, but the only hormone that stimulates it is ghrelin, which signals the need to fill the stomach. A further study of laboratory mice showed that ultraviolet radiation increases the secretion of ghrelin by fat cells located in the skin. In female mice (and women) this does not occur because ghrelin production is blocked by the female sex hormone estrogen. Scientists tested this theory by taking skin samples from men, and found that ultraviolet light caused increased secretion of ghrelin.
Whether increased appetite affects weight gain, Israeli researchers did not study.