Tuesday, April 20, 2010

Exercise, weight loss and dementia

It's not that exercise doesn't work as a weight loss method, it's just inefficient ....
Weighing the Evidence on Exercise - NYTimes.com:
... When researchers affiliated with the Pennington center had volunteers reduce their energy balance for a study last year by either cutting their calorie intakes by 25 percent or increasing their daily exercise by 12.5 percent and cutting their calories by 12.5 percent, everyone involved lost weight. They all lost about the same amount of weight too — about a pound a week. But in the exercising group, the dose of exercise required was nearly an hour a day of moderate-intensity activity, what the federal government currently recommends for weight loss but “a lot more than what many people would be able or willing to do,” Ravussin says."
An hour a day would be wonderful -- if my kids were grown.

The NYT article has the complex details. The effect of exercise on weight varies by age and gender, and between individuals as well. In general, however, it's not a good way to lose weight. Diet is more efficient.

On the other hand exercise seems to be essential to keeping weight stable after a weight loss diet. How and why? Nobody knows for sure.

Sitting turns out to be really, really, bad. We've had hints of that over the past years, but now it's getting pinned down. We don't know why, but sitting promotes obesity.

Incidentally, it's all harder for women. But you knew that.

Elsewhere in the NYT, Olivia Judson deepens the cheer with claims that obesity causes brain damage. She's a bit below her par though; she obscures correlation with causation in the interests of more hits(she well knows the difference, so two demerits to her). It is likely that obesity is associated with early dementia, but it's also associated with lower socioeconomic status, lower IQ, and the anger of the gods.

On the other hand, there's a weird association between exercise and brain function, even though I didn't believe it years ago. Exercise seems to help the health of neurons associated with cognition and memory in various animals -- for no particularly good reason. Since exercise is associated with lower obesity (in both directions) this further murkens the muddies.

Exercise also seems to help sleep, and I do suspect that sleep will turn out to be very important for brain health. Since obesity does impact sleep quality there may be an effect of obesity on the brain both by diminishing interest/ability to exercise and by worsening sleep quality.

Lastly, the idea that brain activity (bridge, crosswords, etc) slows dementia seems to be, at long last, good and dead. It doesn't work. Forget the bridge, forget the crosswords, go for a walk.

To sum it all up, my best guess at how this will all turn out:
  • Sleep is more important for brain health than we've imagined.
  • Exercise is more important for brain health than I thought 4-7 years ago. (I like to exercise, so it wasn't a prejudice against activity. It's just weird science.)
  • Exercise helps both sleep and brain health - so it's a double good. It doesn't lead to weight loss, but it's essential to maintain a stable weight.
  • We all need to diet all the time, so we need cultural and industry changes to make that very hard activity easier.
  • Obesity is almost inevitable in a food rich world, especially when we eliminate smoking and increase sitting (at computers). We need a miracle drug, we need cultural changes, we need mobile devices, we need gas to hit $10 a gallon.
  • Sitting is oddly bad for us. We should all be standing and walking.
  • Try not to get a concussion (but almost all enjoyable exercise increases head injury risk :-). Don't let your kids play football (which will eventually go the way of boxing).
See also:

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