Being fat is bad for your brain.
That, at least, is the gloomy conclusion of several recent studies. For example, one long-term study of more than 6,500 people in northern California found that those who were fat around the middle at age 40 were more likely to succumb to dementia in their 70s. A long-term study in Sweden found that, compared to thinner people, those who were overweight in their 40s experienced a more rapid, and more pronounced, decline in brain function over the next several decades.
Consistent with this, the brains of obese people often show signs of damage. One study of 60 healthy young adults (in their 20s and 30s) found that the fatter members of the group had significantly lower gray-matter densities in several brain regions, including those involved in the perception of taste and the regulation of eating behavior. A study of 114 middle-aged people (aged between 40 and 66) found that the obese tended to have smaller, more atrophied brains than thinner people; other studies have found similar results.
Brains usually atrophy with age, but being obese appears to accelerate the process. This is bad news: pronounced brain atrophy is a feature of dementia.
Why fatness should affect the brain in this way is not clear, although a host of culprits have been suggested. A paper published this week in the early edition of Proceedings of the National Academy of Sciences has identified a gene that seems to be involved. FTO, as the gene is known, appears to play a role in both body weight and brain function. This gene comes in different versions; one version -- let's call it "troublesome"-- appears to predispose people to obesity. Individuals with two copies of the troublesome version tend to be fatter than those with only one copy of it, who in turn tend to be fatter than those with two copies of the "regular" version. Now, the troublesome form has been linked to atrophy in several regions of the brain, including the frontal lobes, though how and why it has this effect remains unknown.