The participants also underwent memory tests before and after going on the diet. At the end of three months, the calorie-restricted group increased its scores by about 20 percent, while the performance in the other groups did not change. Flöel says that it’s not clear why eating healthier fats did not seem to benefit the brain in this trial, but her team is now investigating whether boosting just omega-3 fatty acids, rather than all unsaturated fats, could have a stronger effect.
Mattson says that, in addition to showing a boost in memory, the study also suggests that the same underlying mechanisms uncovered in animals could be at work in humans too. The researchers found that people who cut calories had improvements in several indicators of metabolic health, such as blood levels of insulin and C-reactive protein, a marker of inflammation. In fact, the rise in cognitive test scores correlated with lower insulin levels. In animal studies, high insulin levels and low-grade inflammation–products of being overweight and of high calorie intake–have been shown to hamper cognitive function. Mattson says that limiting calories in mice boosts a molecule in the brain called BDNF, which has a key role in memory. Regular exercise, along with calorie restriction, also boosts the growth of new brain cells in mice. Flöel says that the current results “suggest that those pathways from animal studies might also work in humans.”
However, Mattson cautions that older adults are at a higher risk of nutrient deficiencies, and could experience health problems that outweigh the potential benefits if they cut back on calories too severely. “Not everyone is going to benefit from calorie restriction,” he says. But for those who are already consuming more than they need and have a little extra weight to spare, there’s yet another health reason to cut back.