Based on a meta-analysis of 20 studies, mental performance may be improved with even moderate

weight loss among overweight individuals, though that may be due not to the weight loss per se,

but rather the prescribed exercise.

For example, one study randomized obese elders to one of four groups for a year.

A weight loss diet alone, exercise without weight loss, both or neither.

Compared to the control group that did neither, global cognition improved in all the three

other groups.

But while weight loss and exercise beat out weight

loss alone, weight loss and exercise didn't beat the exercise alone, suggesting that exercise

is the most potent component. The American College of Sports Medicine cites meta-analyses

of dozens of prospective studies following tens of thousands of people for years that suggest

that those who are active have a 38% lower risk of cognitive decline. dozens of prospective studies following tens of thousands of people for years that suggest that

those who are active have a 38% lower risk of cognitive decline and a 39% lower risk of developing

Alzheimer's disease. And apparently, the more, the better. Every extra 500 calories expended a week

appears to correlate with an additional 10% drop in dementia risk.

However, even light physical activities such as low-intensity walking or how yoga and

tai-chi are often practiced by older adults has been associated with at least some sort of

cognitive gain in about half the studies done to date. If the relationship between exercise and dementia prevention is cause and effect, as much

as 20% of all cases of Alzheimer's disease in Western countries may be attributable to physical

inactivity.

That would mean more than a million cases of Alzheimer's just in the U.S. alone. As with all observational data, though,

there's the potential for confounding or reverse causation. Maybe there's a shared factor causing

...