For Carole Carson, the golden years weren't so shiny when it came to her mental clarity.
"I was sort of a retired lump on a log," said 67-year-old Carson, referring to herself seven years ago.
But after going on a restricted calorie diet, along with an exercise regime, Carson, who lives in Nevada City, Calif., lost about 50 pounds. Her life -- and her mind -- perked up again.
"Every kind of mental function improved," Carson said.
Many people who have cut calories experience the "mental clarity" and increased creativity Carson said was an unexpected benefit of a healthier lifestyle.
Now, researchers have shown a definite link between caloric restriction (CR) and mental function, according to a study published Monday in the journal Proceedings of the National Academy of Sciences.
Researchers from the University of Munster in Germany divided 50 normal and overweight adults with an average age of 60 years into three groups. Group 1 cut their normal daily caloric intake by 30 percent, group 2 increased their normal daily consumption of unsaturated fatty acids, such as those found in fish and olive oil, and group 3 did not alter anything in their diets.
The volunteers had their memories tested at the start of the study and again three months later. Results showed that those who reduced their calorie consumption improved their scores on a word-learning task, suggesting a boost in verbal memory. Other types of memory were not affected, and the other two groups showed no significant cognitive improvements.
But while this study does show a link, the number of participants was small, making it difficult to determine how the dietary programs would affect a wider population. Past studies have not shown a clear relationship between cutting calories and memory.
"We do not yet know if this response is sustained over time and whether it is meaningful enough to benefit our everyday activities," said Dr. P. Murali Doraiswamy, professor of psychiatry and medicine at the Duke University Medical Center.
But experts agreed that the phenomenon makes sense from a physiological standpoint. Dr. Ken Fujioka, director of Nutrition and Metabolic Research at the Scripps Clinic in San Diego, offered an evolution-based explanation.
"Humans used to die from starvation all the time," he said. "Insulin is a messenger to the brain of carbohydrate reserves, and as we restrict calories, we will drop the insulin and signal to the brain we will be going into 'starvation.' It would be adaptive to have better verbal memory to find food or calories in order to survive."
In addition to increased insulin sensitivity, the researchers proposed that better neuron function and reduced inflammatory activity, as a result of caloric restriction, could have resulted in better verbal memory.
Along with her overall well-being, Carson said she noticed clear cognitive benefits from CR after just a few months of her new diet.
"Is my verbal memory improved? Absolutely," she said.
In the past several years, Carson has organized a community weight-loss effort, gives talks about her own weight loss -- from memory -- and has published two children's books.
"I have to use my memory in incredible ways," said Carson, who just bought a new laptop on which she receives about 500 e-mails a week due to her busy schedule, far busier than when she ran her own business prior to retiring. "Something has shifted."
Further research on CR and cognition could have implications for those with Alzheimer's or stroke-related memory loss.
"Our study may help to generate novel prevention strategies to maintain cognitive functions into old age," the authors wrote in the paper.