How the brain reacts
Mattson has, however, identified another effect of fasting that he believes can benefit everyone: It is good for the brain. "If you look at an animal that's gone without food for an entire day, it becomes more active," he says. "Fasting is a mild stressor that motivates the animal to increase activity in the brain." From an evolutionary perspective, this makes sense, because if you are deprived of food, your brain needs to work harder to help you find something to eat.
His studies suggest that alternate-day fasting, with a single meal of about 600 calories on the fast day, can boost the production of a protein called brain-derived neurotrophic factor by 50 to 400 percent, depending on the brain region. This protein is involved in the generation of new brain cells and plays a role in learning and memory. It can also protect brain cells from the changes associated with Alzheimer's and Parkinson's. In mice engineered to develop Alzheimer's-like symptoms, alternate-day fasting begun in middle age delayed the onset of memory problems by about six months. "This is a large effect," Mattson says, perhaps equivalent to 20 years in humans.
So, what about the common advice to start the day with a good breakfast? Mattson believes it is flawed, pointing out that the studies supporting this idea were based on schoolchildren who usually ate breakfast; a decline in their academic performance might simply be due to the ill effects that occur when people begin fasting.
Mattson skips breakfast and lunch five days a week, then has dinner and normal weekend meals with his family. Varady has tried alternate-day fasting, but she likes to eat dinner with her 18-month-old child and husband, so she does all her eating within an eight-hour period each day.