Did Grandma seem forgetful at the holiday parties last month? It could be time to put her on a diet. Sharply reducing calories improves memory in older adults, according to one of the first studies of dietary restriction and cognitive function in humans.
Research on the benefits of an extremely low-calorie diet stretches back to the 1930s, when scientists found that rats lived up to twice as long when they nibbled less than control animals. Since then, some studies with rodents and nonhuman primates have shown that this spare diet, known as calorie restriction, improves some markers of diabetes and heart disease, such as blood glucose and triglyceride levels, and possibly prevents neurological declines similar to those seen with Alzheimer's disease and Parkinson's disease. In humans, however, the results have been mixed. Subjects on low-calorie diets generally have lower blood pressure and blood sugar levels than their chow-happy counterparts. But these studies were small, and none was designed to test how calorie restriction might affect cognitive performance.
To fill that void, neurologist Agnes Flöel and her colleagues at the University of Muenster in Germany recruited 50 healthy elderly subjects. The average volunteer was 60 years old and overweight, with a body mass index of 28. The researchers randomly assigned the volunteers to one of three groups. Twenty people were instructed to reduce their daily calorie intake by 30%, while still eating a balanced diet of nutrient-rich carbohydrates, fats, and lean proteins. Another 20 were told to keep their caloric intake the same but increase their consumption of unsaturated fatty acids, such as those found in salmon or olive oil. (Previous studies have linked a diet rich in these fats to improved cognition.) The remaining 10 volunteers did not change their diets.
After 3 months, all of the volunteers took a memory test in which they were shown 15 words and asked how many they could remember after 30 minutes. On average, those in the calorie-restriction group showed a 20% improvement over their baseline memory scores taken before they started their diets. Subjects in the other two groups showed little or no improvement, the researchers report online this week in the Proceedings of the National Academy of Sciences. "Our study only provides some of the first evidence on the impact of [calorie restriction] on memory in the elderly, but this study has to be followed up now," Flöel wrote in an e-mail to Science. Her team plans to conduct larger studies to determine exactly how calorie restriction enhances memory.
Neuroscientist Laura Dugan of University of California, San Diego, cautions that subjects in the study were overweight at the outset, so their memory improvement could have come from returning to a healthier body weight rather than from simple calorie restriction. Being overweight can cause sleep apnea, for example, which could interfere with cognitive function. But Giulio Pasinetti, a neuroscientist at Mount Sinai School of Medicine in New York City, praises the study as the first controlled test of calorie restriction and memory. "The most important message is that moderation in lifestyle--dietary lifestyle--is probably beneficial for our mental activities," he says.