Although our brain accounts for just 2 percent of
our body weight, the organ consumes half of our daily carbohydrate
requirements—and glucose is its most important fuel. Under acute stress
the brain requires some 12 percent more energy, leading many to reach
for sugary snacks.
Carbohydrates provide the body with the quickest
source of energy. In fact, in cognitive tests subjects who were stressed
performed poorly prior to eating. Their performance, however, went back
to normal after consuming food.
When we are hungry, a whole network of brain regions activates. At the
center are the ventromedial hypothalamus (VMH) and the lateral
hypothalamus. These two regions in the upper brain stem are involved in
regulating metabolism, feeding behavior and digestive functions. There
is, however, an upstream gatekeeper, the nucleus arcuatus (ARH) in the
hypothalamus. If it registers that the brain itself lacks glucose, this
gatekeeper blocks information from the rest of the body. That’s why we
resort to carbohydrates as soon as the brain indicates a need for
energy, even if the rest of the body is well supplied.