"The positive effects of carbohydrates on cognition have been well-established by previous research, but this is the first study to show that pure dietary protein and fat also improve memory," says lead author Randall Kaplan, a PhD candidate in the University of Toronto's Department of Nutritional Sciences and a researcher at the Baycrest Centre for Geriatric Care. Until now, scientists believed that increases in blood glucose levels explained the beneficial impact of carbohydrates on memory in elderly people. In the present study, however, people performed better on memory tests after consuming carbohydrate, fat and protein drinks of equal calories compared to a placebo with no food energy, regardless of the drinks' effects on blood glucose levels.
The positive results occurred in verbal recall tests administered 15 minutes after the participants -- 11 males and 11 females, aged 61 to 79 -- consumed each type of drink. "The fact that memory was enhanced soon after the ingestion of energy from any macronutrient may be explained from an evolutionary perspective," Kaplan says. "A mechanism that would allow an animal to remember the details of a successful hunt for food would clearly be beneficial for survival."
Other memory tests involving attention and non-verbal tasks showed variable effects, he says, suggesting that specific types of food energy enhance specific aspects of brain function. Further research is necessary to unravel the unique connections between each nutrient and brain region involved in memory. "The proportion of North Americans with cognitive impairments is increasing as the population ages, so it's important to understand environmental factors such as nutrition that may help to prevent or reduce these deficits," he says.
The research was funded by the Natural Sciences and Engineering Research Council and the Canadian Institutes of Health Research.