Heat can make you gain WEIGHT – if you’re a man, study shows

With temperatures hitting 86°F (30°C) in parts of the UK this week, many of us may be tempted to grab an ice cream or a few chilled pints of beer in the beer garden.

But scientists say it may not be just our desire to cool off that makes us crave those extra treats while out in the sun.

A new study has shown that exposure to sunlight stimulates the release of the hunger hormone from the skin, but this effect is specific to men.

Researchers from Tel Aviv A university in Israel claims that men are more likely to gain weight in the summer because of this hormone.

However, in women, the sex hormone estrogen interferes with the release of this hunger hormone, which means it does not result in a change in appetite.

“These results indicate that the skin is a major mediator of energy homeostasis and may open up therapeutic options for the treatment of endocrine diseases through sex,” the scientists wrote.

A new study has shown that exposure to sunlight stimulates the release of the hunger hormone from the skin, but this effect only occurs in men (file image).

In women, the sex hormone estrogen prevents the release of this hunger hormone, meaning it does not change appetite.

In women, the sex hormone estrogen prevents the release of this hunger hormone, meaning it does not change appetite.

Scatter plot of monthly energy intake (kcal per day) from 1999 to 2001 for 2991 men (blue) and women (pink).  Men's energy intake was significantly higher in summer (2188 kcal versus 1875 kcal), while women's energy intake remained constant.

Scatter plot of monthly energy intake (kcal per day) from 1999 to 2001 for 2991 men (blue) and women (pink). Men’s energy intake was significantly higher in summer (2188 kcal versus 1875 kcal), while women’s energy intake remained constant.

Exposure to UV-B stimulates foraging in males but not in females.  In male skin adipocytes, the p53 protein increases ghrelin transcription.  However, in women, estrogens block this transcription, so they don't have this increase in appetite.

Exposure to UV-B stimulates foraging in males but not in females. In male skin adipocytes, the p53 protein increases ghrelin transcription. However, in women, estrogens block this transcription, so they don’t have this increase in appetite.

WHAT IS GRELIN?

Ghrelin is known as the “hunger hormone” because it stimulates appetite, increases food intake, and promotes fat storage.

It is released primarily by the stomach, with small amounts also excreted by the small intestine, pancreas, and brain.

It circulates in the bloodstream and acts on the hypothalamus, an area of ​​the brain critical for appetite control.

Ghrelin has also been shown to act on areas of the brain involved in reward processing, such as the amygdala, and may stimulate activity of dopamine neurons.

Blood levels of ghrelin rise just before meals and during fasting, with the timing of this rise depending on our usual eating patterns.

Source: you and your hormones

The need for food is mainly controlled by communication between peripheral tissues such as the intestines and liver and the brain.

Hormones are released from peripheral organs and reach areas of the brain such as the hypothalamus, which controls functions such as temperature and sleep, as well as hunger.

A study published today in Nature Metabolismstudied the results of a survey of 3,000 Israeli participants who recorded their diets between 1999 and 2001.

Carmit Levy and her team noticed that men, on average, increase their calorie intake from food during the summer months, when solar radiation is highest.

However, a similar summer peak was not observed in women.

The study was supported by a study of mice that were exposed to ultraviolet (UV) radiation daily for ten weeks.

The researchers observed a “significant increase in food intake” in male mice, but not in female mice.

Ultraviolet light has been found to stimulate the release of the hunger hormone ghrelin from fat cells in male mouse skin tissue called adipocytes.

Once reaching the hypothalamus, ghrelin increased appetite in these male mice, promoting food intake and weight gain.

The researchers also noted that the mice exhibited increased food-seeking behavior, suggesting that increased food intake was also associated with the beneficial properties of the food, and not just meeting the energy requirement.

However, this effect was blunted in female mice because the sex hormone estrogen interfered with the release of ghrelin from fat cells in the skin.

Female mice with low circulating estrogen levels also consumed more food when exposed to UVB.

The researchers conducted three more experiments, two of which examined cultures of human cells in the laboratory and their response to UV radiation.

Results of male mice subjected to the

Results of male mice subjected to the “ladder test” where they have to paw down a narrow ladder from an elevated platform in order to grab the desired food. The results showed that males treated with UV-B ate significantly more food pellets than males not exposed to UV-B (control).

Results of female mice subjected to the

Results of female mice subjected to the “ladder test”. Females exposed to UV-B had a modest reduction in food intake compared to those not exposed to UV-B (control).

Average weekly body weights of male (left) and female (right) mice, some of which were exposed to UV-B radiation (blue) or served as controls (grey).  Males exposed to UV-B showed weight gain compared to the control group, while females exposed to UV-B and the control group had no significant difference.

Average weekly body weights of male (left) and female (right) mice, some of which were exposed to UV-B radiation (blue) or served as controls (grey). Males exposed to UV-B showed weight gain compared to the control group, while females exposed to UV-B and the control group had no significant difference.

They found that samples of human male skin exposed to UV-B for five days resulted in an increase in ghrelin expression.

In another experiment, the appetite of people with skin conditions treated with UV-B light therapy was studied.

Men generally reported feeling more hungry a month after starting treatment, but women reported no change in their appetite.

The researchers believe their results identify sebum as a possible regulator of eating behavior, adding a new type of adipose tissue to the energy balance equation.

However, Professor Kevin McConway, Emeritus Professor of Applied Statistics at the Open University, believes that other factors could have influenced these results.

He said: “The results in mice and cell cultures, as well as other studies in humans, at least make it plausible that solar radiation and sex differences may be associated with the occurrence of patterns, but they cannot rule out other possible explanations.”

“It is also likely that men and women behave differently with respect to sunny weather for social reasons.

“Because of social norms and customs regarding how much skin men and women can expose to the sun, because of the different jobs they can do, or because of a long list of other reasons, and that all of this can have some related to differences in calorie expenditure.

Duane Mellor, registered dietitian and senior scientist at Aston Medical School, added: “This study provides five pieces of a very interesting scientific puzzle, but unfortunately, gaps in the data make the pieces not quite fit together.

“What it does show is a potential mechanism for how UV-B can affect hormone metabolism, which is similar to how it works to help our skin produce vitamin D, and how this could be related to an increase in male appetite hormone ghrelin. at least in mice.

“It is important to recognize that this article does not claim that exposure to sunlight and UV-B will cause weight gain in men.

“Instead, it provides some interesting insights into how moderate UV-B exposure may be associated with health benefits, including reduced risk of cardiovascular disease and inflammation, as ghrelin has anti-inflammatory effects.

“It’s also important to remember that when most people are exposed to increased UV-B exposure from sunlight, they may also be more physically active, which may partly explain more food intake, although there is no data in this current study to support this.”

WHAT WAYS TO KEEP COOL DURING THE HEAT?

The NHS has some tips for staying cool during unusually hot weather.

– Drink plenty of fluids

– Open windows or other vents in the house

– Shade or cover windows that are exposed to direct sunlight.

– Grow plants indoors and outdoors to provide shade and cool the air

– Turn off lights and electrical equipment that is not in use.

– Take a break if your house gets too hot: go to the nearest air-conditioned building, like the library or the supermarket.