Obesity and Mental Function

There are certainly more important things going on, but I can't resist a flawed study (or flawed reporting of a good study). Today it's this study, reported Monday by Reuters, on the connection between obesity and cognition. Here are the facts:

The study included 2,223 healthy French adults who were between the ages of 32 and 62 in 1996. At that time, they took a battery of standard cognitive tests, assessing abilities like memory, attention and speed of learning. Five years later, they took the tests again.

In general, the researchers found, people with a high body mass index (BMI) garnered lower test scores than those with a lower BMI. They also tended to show greater cognitive decline between the two test periods.

So far, so good. Fat people have lower cognitive results, and they decline more, than thinner people do.

But the article goes into what appears to be speculation:

The findings, they say, suggest that a heavier weight in middle age may mean a higher risk of dementia later in life.

"Our results, along with other previous studies, strongly suggest a greater risk of dementia in these (overweight) persons at middle-age," Cournot told Reuters Heath.

What results of their study showed a higher rate of dementia among fat people? What studies show that lower cognitive ability in middle age leads to dementia? Maybe lower cognitive ability in middle age only leads to lower cognitive ability in old age. Maybe. The article doesn't have a link to the actual study being discussed or to related studies.

So I googled the study and came up with a bunch of other articles talking about it. A Fox News article goes into more detail about the study, then offers these hypotheses to explain the obesity-lower cognition correlation:

What's behind the link? "There are two strong hypotheses," Cournot says. Since obesity can lead to heart and blood vessel disease, including hardening of the blood vessels or atherosclerosis, the brain's blood vessels might be affected and not function as well.

Excess weight can also lead to poorer management of the body's insulin, and that could be affecting brain cells as well.

I can see another explanation, one that looks at what we already know about the brain: When we use our brains, they develop stronger, more complex neural connections, which in turn helps us use our brains more effectively.

When kids (or adults) are plunked in front of the TV for hours on end, they don't develop the complex neural networks that allow for strong cognitive ability. But send a kid outside to play, where he can interact with others and be challenged, or give him some good books to read and puzzles to play with, and those neurons will be stimulated, improving his mental function.

TV Slugs of any age tend to get fat. TV Slugs of any age tend not to be as strong cognitively. In my book, there's a strong likelihood for a common cause of both obesity and poor cognitive ability, and that is inactivity/lack of mental stimulation during childhood. In fact, the Fox News article could be used to support this:

Others familiar with the association say the new study makes sense. "It provides even more support for the ideas that there is a link between excess weight and brain function," says John Gunstad, PhD, an assistant professor of psychology at Kent State University in Kent, Ohio. He gave 486 healthy adults, aged 21 to 82, memory tests and also found that an obese BMI, at any age, reduced memory performance. In his study, published in March 2006 in the journal Eating and Weight Disorders, he found a relationship between obesity and reduced memory performance to be independent of a person's age. (emphasis added)

Both the Reuters and Fox News articles bandied about the word, "Alzheimer's," quoting various researchers who speculated that Alzheimer's could be the end result of obesity's alleged influence on mental performance. But over at the Alzheimer's website, the page on "What is Alzheimer's" makes a distinction between Alzheimer's Disease and vascular dementia. It describes vascular dementia as, "result[ing] from reduced blood flow to the brain’s nerve cells."

So heart disease, which can be but isn't always associated with obesity, can lead to vascular dementia. But not necessarily the other forms of dementia.

In the end, the results of this study boil down to this: If you're fat, you might be stupid. If you're fat and stupid, you'll probably stay that way. All the rest of it is still speculation.