THE heatwave could be making men fatter, science suggests.

Men may eat more calories in the summer, but womens' appetites don't change.

Tel Aviv University in Israel used existing data on about 3,000 people who had filled in a detailed dietary questionnaire over 12 months. 

Between March and September, men consumed about 17 per cent more calories per day than they did during the rest of the year, the study showed.

Women’s food intake stayed about the same, New Scientist reported.

Dr Carmit Levy, lead author, said it could be that sunlight causes men to produce more of the hormone ghrelin – one of many appetite stimulating hormones.

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The theory was tested on mice by Dr Levy and her team at the Department of Human Molecular Genetics and Biochemist.

They exposed a group of male mice to UVB radiation – found in sunlight – and discovered that they had raised levels of ghrelin secretion by fat cells in their skin.

This was blocked by the female sex hormone oestrogen, which may explain why women did not eat more calories in the summer.

The mice increased their food intake and food-seeking behaviour, researchers reported in the journal Nature Metabolism.

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The findings were further supported by human studies – five men were exposed to UV in the lab for 25 minutes for five days.

They had higher ghrelin in their skin cells, but female participants did not react in the same way. 

Levy suggested the phenomenon was an evolutionary tool in which the body is driven to refuel with food when the weather is warm, or to provide energy for more physical activity. 

She said: “The skin is the largest organ of the body, so it makes sense that this huge organ can sense the environment, sensing that there is UV now, that now is the time to go out.”

The team didn’t look at whether the men actually gained weight in the summer due to raging hunger hormones and more food consumption.

Dr Mir Ali, medical director of MemorialCare Surgical Weight Loss Center at Orange Coast Medical Center, California, who was not involved in the study, told Medical News Today: “Age, genetic predisposition, activity level and concurrent health conditions all affect hormonal secretion.

“Much more research is necessary to understand how we can use this information to help someone attain and maintain a healthy weight.”

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Caroline Gorvin at the University of Birmingham said it hadn’t been shown before that skin was involved in appetite.

She added: “If it’s real, it’s quite exciting.”

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