New Study Shows How People Eat More After Intellectual Work
The human brain needs a lot of energy to carry out its complex functions. When the body is at rest, so the muscles aren't consuming a lot of energy, it is estimated that the brain uses 20% of the total energy used by the whole body, and a whopping 60% of the glucose (muscles can use fat for a lot of their energy, but the brain can't).
The brain constitutes only 2% of the weight of the body, so its energy use is disproportionately large in comparison to its size.
Because of this relatively large energy consumption by the brain, I've always thought that perhaps if I spent a lot of time lounging around and thinking, I could increase my brain's utilization of glucose and energy, lower my blood glucose levels, and lose a lot of weight without having to walk for miles or lift weights for hours.
Unfortunately, someone once did a study of college students taking final exams and found that the increase in metabolism during the exams was miniscule, and they attributed it primarily to muscular tension.
Now comes a study suggesting that increased mental effort, instead of helping us lose weight, might actually make us gain.
A research team at Laval University in Quebec, led by Dr. Angelo Tremblay, has found that after difficult intellectual work, people tend to eat more, even though they don't feel any hungrier.
The researchers measured the food intake of 14 female students after relaxing in a sitting position, reading and summarizing a text, and completing a "comprehensive battery of computerized tests." The intellectual tasks were estimated to require only 3 more calories than sitting and relaxing.
After 45 minutes of these activities, the students were taken to a buffet and told to eat as much as they wanted. The students who summarized a text ate an extra 203 more calories and the students doing the computer work ate 253 more calories than the students sitting and relaxing, despite the fact that they burned only an extra 3 calories. The difference between the two intellectual tasks was not statistically significant.
The increased food intake after the intellectual work was not balanced by lower food intake for the rest of the day.
Blood tests showed that cortisol levels were higher in the students taking the tests, and the students doing the intellectual work also had greater fluctuations (2.2 and 8.3 times larger) in blood glucose and insulin levels than the students sitting and relaxing.
The authors speculated that perhaps these glucose and insulin fluctuations triggered the extra food intake. Cortisol has also been shown in previous research to result in greater food intake.
I think it might also be psychological. When I get good news, I tend to run to the fridge to have something to eat to celebrate. When I get bad news, I tend to run to the fridge to console myself. When I've been doing something difficult, either a mental task or a physical one, when it's done, I want to sit down, have a nice cuppa java, and have something to eat.
If I've been just sitting and relaxing, with no stress, I'm not apt to want to eat until I'm very hungry. So the students' response makes perfect sense to me.
Some research has also suggested that eating can serve as a "consolation and/or compensation" for emotional stress. Other research has shown an increase in chocolate intake after a cognitive task.
Regardless of the reason for the effect, the authors of the paper speculate that because so many people these days are doing intellectual work rather than hoeing corn or digging ditches, this might account for the "obesity epidemic" everyone is talking and writing about.
The physical labor would undoubtedly cause increased appetite. But because one also needs more calories when doing physical work, those increased calories might not contribute to weight gain.
The students didn't report feeling extra hungry. They just ate more. And eating more without compensating with physical activity can lead to weight gain.
Time will tell if this finding is a major contributor to the current trend toward gaining weight in industrialized countries. It's probably just one more small piece of the puzzle.
But in the meantime, I think I'll do my serious thinking after lunch, rather than before.