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Junk food diet worse for male brains

Mouse study Stuffing down a burger and coke may be more harmful for men than women, if the results of a new mouse study apply to humans.

The detrimental impact of junk food seems to be connected to inflammation in the brains of male mice, with the brains of females protected by oestrogen, according to research published today in Cell Reports.

Dr Deborah Clegg, who led the study while at University of Texas Southwestern Medical Centre, Dallas, USA, was building on existing research that links brain inflammation with obesity and heart disease in male mice.

"We embarked on this research because [the link with inflammation] had been shown in male mice, so we asked ourselves, do the same processes occur in females?" explains Clegg.

Previous research has shown that one cause of inflammation in the hypothalamus - the part of the brain that controls energy balance - is palmitic acid, a saturated fatty acid found in palm oil, dairy products and meat, and common in high fat food.

The team looked at male and female mice, fed either their normal diet or a 'high fat' diet. Besides containing 42 per cent fat, the high fat diet was also high in carbohydrates making it a good correlate of human junk food, says Clegg.

"The high fat food was tasty - like cookie dough," says Clegg. "It would be like eating a burger and a coke."

After 16 weeks on the high fat- junk food diet the male mice showed markers of inflammation in their brains - but there was no inflammation in the female mice's hypothalamuses.

"It completely surprised us. It was shocking that we didn't see the inflammation," says Clegg.

They also found that male mice on the junk food diet were more likely than females to become glucose-intolerant and to have impaired heart function.

The team went on to demonstrate that a particular type of oestrogen receptor was protecting the female brain from inflammation.

This fits nicely with the fact that premenopausal women (who have high levels of oestrogen) suffer far fewer harmful effects of obesity, such as diabetes and heart disease, than men. Once women reach menopause, though, they are no longer protected.

No sex equality when it comes to fat

Another surprise finding was that male and female brains are different in terms of their fatty acid composition, even when comparing male and female mice on the normal diet.

"It was striking. The male brain more mirrors the composition of the fatty acids in the diet they consumed. The female brain doesn't.

"We found there was more palmitic acid and that ceramide levels were higher in the male brain. And linoleic acid was absolutely missing in the male brain but was elevated in the female brain."

She says as far as she is aware this is the first time that differences in brain fat composition have been noted in the two sexes.

"I've never seen data like this before," she says.

Clegg is now working at Cedars-Sinai Medical Centre, Los Angeles, USA where she plans to see whether the results apply to humans.

"I think that's the number one question. The work was all done in mice and now it begs to be done in humans."

Commenting on the paper, Professor Margaret Morris of the University of New South Wales says: "I think it's a really amazing story. It's a very interesting and complete investigation."

"We think diet is partly affecting the brain through an inflammatory response, and their thesis is that this is different in males and females because of oestrogen acting at the oestrogen receptor in females."

Morris says that Clegg's study points the finger at palmitic acid as the component in the diet that is driving inflammation.

However, Morris's team are doing similar research and they have found that sugar can cause hypothalamic inflammation in rats.

"It could be that there are multiple drivers [of inflammation]. It's a fascinating area," she concludes.