Obesity causes brains to shrink – increasing the risk of Alzheimer’s disease later in life, researchers say.

A study has found that people who carry a gene linked to overeating and excess body weight tend to have smaller brains than the rest of the population.

The finding adds to the evidence that obesity is a cause of dementia – and raises new concerns that the obesity epidemic sweeping the West could send Alzheimer’s rates soaring.

The findings come from brain scans of 206 healthy pensioners.

Scientists found that those carrying a gene mutation called FTO had 8 per cent fewer cells in the frontal lobes of the brain –the region involved in making complex judgments.

They also had 12 per cent fewer brain cells in the occipital lobes involved in processing mental images.

The fatter the volunteers, the more the damage.

Shrinkage of the brain is an indicator of Alzheimer’s disease.

The faulty FTO gene can cause people to overeat. It is carried by almost half of white Europeans but only 16 per cent of Asians.

Neurologist Paul Thompson, who led the study at the University of California, said the differences in brain size could not be directly linked to other by-products of obesity – such as cholesterol levels, diabetes or high blood pressure.

However, the researchers are unsure exactly how the gene shrinks the brain – or how it makes people fat.

Dr Susanne Sorensen, of the Alzheimer’s Society, said: ‘This is a relatively small study but the findings support the need for more research. One million people will develop dementia in the next 10 years but dementia research is desperately underfunded. With the right investment, it can be defeated.’

The findings are published in the Proceedings of the National Academy of Sciences journal. The Daily Mail