Cutting calories by 30 percent for three months led to a significant improvement in memory in a group of elderly people, according to recent research.
These results add to previous evidence from animal studies suggesting caloric restriction may protect neurons and benefit brain function. Studies in animals and humans also have indicated that cutting calories may increase longevity.
Neurologist Agnes Flöel and colleagues at the University of Münster in Germany assigned 50 healthy people, ages 50 to 80, to one of three groups: a caloric restriction group, who reduced their calorie intake by 30 percent; an unsaturated fatty acid (UFA) group, who increased their intake of UFAs by 20 percent; and a control group, who did not alter their diet.
Subjects in the caloric restriction group not only lost a significant amount of weight, they also showed a 20 percent improvement in verbal memory scores, as measured before and after three months of intervention. No significant memory changes were seen in the UFA group or the control group. The study was published in the Jan. 27 issue of the Proceedings of the National Academy of Sciences.
Flöel and her colleagues also tried to identify potential mechanisms underlying the improvement in memory by testing various metabolic factors thought to contribute to age-related cognitive impairments. In the restricted-calorie group, researchers found a correlation between improved verbal memory scores and a decrease in peripheral levels of insulin and high-sensitivity C-reactive protein (hs-CRP), a general marker of inflammation. The correlation was most pronounced in those who had adhered best to their low-calorie diet.
“The model, which is derived from animal studies, is that if you are able to lower peripheral insulin and glucose, the sensitivity of the brain to insulin rises,” says Flöel. “Insulin signals in the brain rise, and this is actually good for the brain because it is supposed to increase synaptogenesis [the formation of new synapses] and neuronal function.” Likewise, animal studies have suggested that lowering inflammation is good for the brain.
The researchers also tested peripheral levels of the neurotrophic factors IGF-1 and BDNF, but found no significant difference following the dietary intervention. Evidence from animal studies suggests that caloric restriction and exercise increase levels of neurotrophic factors, which are peptides that regulate certain neurons, It is not known how well peripheral levels reflect brain concentrations, Flöel says: “In humans it is really difficult to get a better grip on these factors.”
A weight issue?
“[This study is] a valuable contribution that extends findings from animals to humans and suggests that, at least in overweight subjects, reducing calorie intake does good things for the brain,” says Mark P. Mattson, a senior investigator at the National Institute on Aging who was not involved in the study. “One way to look at it,” he adds, “is that being overweight impairs cognitive function, and that these people were not performing at optimum because they were overweight. When you get in the normal or low weight range, cutting back on calories may not have an effect.”
Flöel acknowledges that the study was not set up to look at weight but says there was no difference in the results for subjects who were in a more normal weight range and overweight subjects. The average body mass index of the subjects was 28; an index of 18.5 to 25 is considered optimal, and more than 30 is classified as obese, according to the National Institutes of Health.
The Münster research group plans a larger follow-up study of caloric restriction that will use magnetic resonance imaging to look at the brain before and after dietary intervention. Flöel says they also will take another look at the effects of fatty acids, adding fish or capsules of omega-3 fatty acids to the diet of the unsaturated fatty acid group.