moins de calories profite à la mémoire

Published online 26 January 2009 | Nature | doi:10.1038/news.2009.57

Elderly people benefit from caloric restriction.

Heidi Ledford

Cutting calories by 30% for three months has boosted memory and reduced insulin concentrations in a group of healthy elderly people.

Previous research on the possible benefits of calorie restriction has yielded mixed results. Some studies have found no benefits. Others have found that calorie restriction protects rats and mice against age-related memory loss and some neurodegenerative diseases. In humans, cutting calories has been linked to prolonged health, but there have been no previous reports of an effect on memory.

Now, neurologist Agnes Flöel and her colleagues at the University of Münster in Germany have filled that gap. The group looked at 50 people divided into three groups: one maintained its usual diet, one was told to cut calories and the third was was asked to eat more polyunsaturated fatty acids — nutrients found in foods such as fish and olive oil that have previously been linked to reducing the risk of cognitive impairment. The participants were either of normal weight or overweight, and averaged just over 60 years old.

Three months later, the researchers found that those who cut calories were 20% better at remembering a list of words than those who either maintained the same diet or ate more polyunsaturated fatty acids. Their work has been published in the Proceedings of the National Academy of Sciences.

"It is an important advance," says Mark Mattson, chief of the laboratory of neurosciences at the National Institute on Aging in Baltimore, Maryland. "It is taking something that was predicted from animal studies and showing that it works in humans."

Sweet success

Memory improved in both normal and overweight people, but the number of participants was too small to allow a thorough comparison of the two groups, says Flöel. She and her colleagues plan to repeat the study in a larger group, and to study the effects of cutting calories in patients with mild cognitive impairment.

Why would cutting calories improve memory? One possibility is that the body becomes more efficient at processing sugar. Participants who cut calories also had lower concentrations of the hormone insulin, which regulates levels of sugar in the blood. Lower insulin suggests that the participants had become more sensitive to the hormone, and previous work has suggested that improved insulin responses can benefit the brain.

In addition, Flöel and her colleagues found lower concentrations of a protein associated with inflammation in the patients who followed a restricted diet. Preliminary studies of that protein, called C-reactive protein, have shown that low concentrations are associated with improved memory in elderly people.

Flöel's study relied on questionnaires filled out by the participants to ascertain whether everyone was sticking to their diets. That has led some to wonder whether the participants really cut calories by 30%. Andrzej Bartke of the Southern Illinois University School of Medicine in Springfield notes that although participants on a reduced-calorie diet lost weight, he might have expected them to lose a little more on such a strict regimen. "Most people would not stick to 30% below what they normally eat," he says. "That's pretty severe. People get hungry."

If some participants broke the rules, however, it suggests that less-draconian measures might also be effective, he says. "It doesn't take very much weight loss to get, in some regard, significantly healthier," says Bartke.

References : Witte, A. V., Fobker, M., Gellner, R., Knecht, S. & Flöel, A. Proc. Natl Acad. Sci. USA 106, 1255–1260 (2009).

http://www.nature.com/news/2009/090126/full/news.2009.57.html