A new study in France found that chronic consumption of refined carbohydrates between meals was associated with worse cognitive performance in both men and women. This effect persisted even when energy intake and a number of other factors were controlled. The study was published in Personality and Individual Differences.
Each animal species is adapted to a specific diet. Their digestive processes tend to be specialized to effectively digest a particular type of food. Due to this, when their diet suddenly changes, this typically leads to health problems as the digestive system is not adapted to the new food types.
For most Western people, a substantial diet change occurred in the second half of the 20th century, when industrialized foods started becoming common. These foods often contained high concentrations of refined carbohydrates – primary sucrose, fiber-depleted gelatinous starches, high sugar corn syrup, and others.
This dietary change was associated with an increase in the occurrence of obesity, type II diabetes, cardiovascular diseases, dental caries, hypertension and many other diseases. The physiological mechanisms involved in the development of these diseases are now thought to involve repeated excessive concentrations of glucose (hyperglycemia) and insulin (hyperinsulinemia) in the bloodstream accompanied by cells becoming less responsive to the effects of insulin (insulin resistance). Glucose is a simple sugar that is the primary energy source in our body, while insulin is a hormone that facilitates the uptake of glucose into cells.
Study author Leonard Guillou and his colleagues wanted to explore whether the consumption of refined carbohydrates affects cognition in healthy young adults. They noted that studies of long-term effects of carbohydrate consumption so far were mostly carried out on older individuals and in the context of certain illnesses. Data on effects of chronic consumption of refined carbohydrates on young, healthy adults are lacking. They organized an experiment.
Participants were 95 healthy young adults between 20 and 30 years of age, recruited at the University of Montpellier in France. They came in groups of 3 or 4 early in the morning to the laboratory. Researchers first measured their blood glucose level. Participants then completed a cognitive assessment test (Wechsler’s digit symbol substitution cognitive test). They were then served one of two types of breakfasts.
Each type of breakfast contained 500 kilocalories, but one was composed of non-refined carbohydrates (whole wheat bread, butter, cheese, a raw fruit and a non-sweetened beverage) and the other of refined carbohydrates (French baguette from industrially milled flour, jam, fruit juice and a non-sweetened beverage with sugar available).
The breakfast to be served was randomly chosen each day. After breakfast, participants completed questionnaires about their demographic characteristics, physical activity levels, and dietary habits. An hour and a half after breakfast, participants’ blood glucose level was measured again and they completed one more cognitive assessment (Wechsler cognitive test). Between these steps, researchers measured participants’ height and weight.
Results showed that 40% of males and 54% of females ate afternoon snacks (corresponding to Le Goûter, a traditional afternoon snack or tea time). 25% of both men and women ate snacks between meals. Higher consumption of refined carbohydrates between meals and higher energy intake in the afternoon snack were associated with worse cognitive performance.
A similar association, but weaker, was observed for energy intake at breakfast. Breakfast consumed on the same day was not associated with cognitive performance. Men, but not women, with higher body mass index values tended to perform worse on the cognitive assessments.
“The recent Western dietary change, characterized mainly by the massive increase in refined carbohydrate consumption, has well-known detrimental health consequences. Given the increasing number of people affected by these pathologies and the repeated failure of many medical treatments, our study reinforces the belief that the most promising research should focus on prevention in healthy persons,” the study authors concluded.
The study makes a valuable contribution to the scientific knowledge about links between dietary choice and cognitive performance. However, it should be noted that the study design does not allow for any cause-and-effect conclusions. It is possible that higher consumption of refined carbohydrates between meals leads to decreased cognitive performance, but it may also be the case that people whose cognitive performance is worse tend to eat lots of refined carbohydrates between meals. These are not the only possibilities.
The study, “Chronic refined carbohydrate consumption measured by glycemic load and variation in cognitive performance in healthy people”, was authored by Leonard Guillou, Valerie Durand, Michel Raymond, and Claire Berticat.