We continue with Sunday's Neuroblogging adventures with a foray into what can only be a contentious field of study, grey matter in the brain...and BMI.

Smith et al. "Decreased gray matter volume in overweight and obese individuals" University of Cambridge, 192.07/UU35

With increased rates of obesity in the United States and elsewhere, a lot of studies have begun to look at effects. While you might have heard about the cardiovascular, the metabolic, and the orthopedic effects of higher BMIs...have you heard about the ones on your brain?

This study was actually a side effect. They had a bunch of healthy controls from a previous study, negative for all psychiatric diseases, addiction, etc, etc. But they noticed some interesting trends, and started correlating the BMI from these healthy individuals with grey matter volumes.

What they found was that, the higher the BMI, the smaller the overall grey matter volume. The correlation has an r=-0.66, a very good correlation in a human study. The differences in grey matter volume appear to be localized to the orbitofrontal cortex and the inferior frontal gyrus.

Of course, with differences in these areas, which are thought to be important in decision making and impulsivity, we have to figure out whether the grey matter deficits translate to functional impairments. So the authors of the study performed a sustained attention task and then an impulse control task, but found no differences. There may be differences in grey matter, but we aren't sure if they DO anything yet.

And then, they found one other difference: cannabis use. It turned out that their samples had significantly higher cannabis use in those with a BMI of over 25 compared to their lower BMI counterparts. But since there was no difference in sustained attention tasks or impulsivity score from the impulse control task, it's not certain why this difference exists, maybe a difference in sensation seeking?

What's particularly interesting about this study is that...the people in it are not that overweight. They have BMIs up to a little above 30, sure, but most of them are not severely obese. Many of the studies looking at grey matter and BMI have examined the severely obese (with BMIs over 40), and also found decreases in grey matter volume. But this is the first to look in a sample of BMIs that represents a much larger percentage of the population, and it goes along with the previous studies of people with higher BMIs, indicating that grey matter decreases as BMI increases.

But the question remains, what are these changes in grey matter for? Why do they exist and are they functional? That's for future studies to find out.