A vertical slice through the brain of a patient with Alzheimer's, left, compared with a normal brain, right. Photograph: Alfred Pasieka/Science Photo Library
Fasting for regular periods could help protect the brain against degenerative illnesses, according to US scientists.
Researchers at the National Institute on Ageing in Baltimore said they had found evidence which shows that periods of stopping virtually all food intake for one or two days a week could protect the brain against some of the worst effects of Alzheimer's, Parkinson's and other ailments.
"Reducing your calorie intake could help your brain, but doing so by cutting your intake of food is not likely to be the best method of triggering this protection. It is likely to be better to go on intermittent bouts of fasting, in which you eat hardly anything at all, and then have periods when you eat as much as you want," said Professor Mark Mattson, head of the institute's laboratory of neurosciences.
"In other words, timing appears to be a crucial element to this process," Mattson told the annual meeting of the American Association for the Advancement of Science in Vancouver.
Cutting daily food intake to around 500 calories – which amounts to little more than a few vegetables and some tea – for two days out of seven had clear beneficial effects in their studies, claimed Mattson, who is also professor of neuroscience at the Johns Hopkins University School of Medicine in Baltimore.
Scientists have known for some time that a low-calorie diet is a recipe for longer life. Rats and mice reared on restricted amounts of food increase their lifespan by up to 40%. A similar effect has been noted in humans. But Mattson and his team have taken this notion further. They argue that starving yourself occasionally can stave off not just ill-health and early death but delay the onset of conditions affecting the brain, including strokes. "Our animal experiments clearly suggest this," said Mattson.
He and his colleagues have also worked out a specific mechanism by which the growth of neurones in the brain could be affected by reduced energy intakes. Amounts of two cellular messaging chemicals are boosted when calorie intake is sharply reduced, said Mattson. These chemical messengers play an important role in boosting the growth of neurones in the brain, a process that would counteract the impact of Alzheimer's and Parkinson's.
"The cells of the brain are put under mild stress that is analogous to the effects of exercise on muscle cells," said Mattson. "The overall effect is beneficial."
The link between reductions in energy intake and the boosting of cell growth in the brain might seem an unlikely one, but Mattson insisted that there were sound evolutionary reasons for believing it to be the case. "When resources became scarce, our ancestors would have had to scrounge for food," said Mattson. "Those whose brains responded best – who remembered where promising sources could be found or recalled how to avoid predators — would have been the ones who got the food. Thus a mechanism linking periods of starvation to neural growth would have evolved."
This model has been worked out using studies of fasting on humans and the resulting impact on their general health – even sufferers from asthma have shown benefits, said Mattson – and from experiments on the impact on the brains of animals affected by the rodent equivalent of Alzheimer's and Parkinson's. Now Mattson's team is preparing to study the impact of fasting on the brain by using MRI scans and other techniques.
If this final link can be established, Mattson said that a person could optimise his or her brain function by subjecting themselves to bouts of "intermittent energy restriction". In other words, they could cut their food intake to a bare minimum for two days a week, while indulging for the other five. "We have found that from a psychological point of view that works quite well. You can put up with having hardly any food for a day if you know that for the next five you can eat what you want."
