Saturday, 27 July 2013
Q. Does extra mental effort burn more calories?
A. Yes, “but it would take years for the difference to show up on the scales,” said David A. Levitsky, professor of nutrition and psychology at Cornell University.
“It is true that the metabolic rate increases when engaged in mental activity,” Dr. Levitsky said. “However, the amount of calories in terms of total daily intake is trivial.”
The amount of energy spent in all the different types of mental activity is rather small, he said. Studies show that it is about 20 percent of the resting metabolic rate, which is about 1,300 calories a day, not of the total metabolic rate, which is about 2,200 calories a day, so the brain uses roughly 300 calories.
“There are good, sophisticated studies that show that concentrated mental activity, like doing a difficult multiplication problem in your head, increases the glucose uptake to the brain,” he said. By how many calories? Less than, say, 20 calories of the 300, he estimated.
But you do not engage that long in such an activity, he said, so the difference might amount to only about 10 calories a day. That means thinking hard is not a good way to lose weight.
There are various ways to measure the brain’s glucose uptake, he said. PET scans of the brain are a noninvasive technique, and there are also actual measurements of glucose in the blood that runs to and from the brain.