We often seek food after focused mental activity, like preparing for an exam. Researchers guess that too much thinking consumes a lot of energy from the brain. So the brain, sensing that it may soon require more calories to keep going, apparently leads to bodily hunger, and even though there has been little physical movement, we eat.
The researchers note that tiring activity both increases the amount of blood sugar and lactate(乳酸盐)circulating in the blood and increases blood flow to the head.
Because the brain uses sugar and lactate as fuel, researchers wondered if the increased flow of fuel—rich blood during exercise could feed a worn—out brain and reduce the urge to overeat.
Thirty—eight healthy college students were invited to determine their fitness and metabolic(新陈代谢)rates and to report what their favorite pizza was. Afterward, they sat quietly for 35 minutes before being given as much of their favorite pizza as they wanted. At a later date, the volunteers returned and spent 20 minutes making selections from college and graduate-school entrance exams.
Next, half the students sat quietly for 15 minutes, before being given pizza. The rest of the volunteers spent those 15 minutes doing intervals on a treadmill(跑步机)two minutes of hard running followed by about one minute of walking, repeated five times. These students were then allowed to gorge on pizza, too. But by and large, they did not overeat.
When the researchers factored in(将……作为因素考虑)the calories burnt on running, they determined that those students actually consumed 200 fewer total calories after their brain workouts than the resting students.
The researchers do not know if the runners consumed extra calories at dinner. They also cannot tell whether other types of exercise would have the same effect as running, although the researchers say they suspect that if an activity causes someone to break into a sweat, it should also increase blood sugar and lactate, feeding the brain and weakening hungers call.
