A new study in France found that chronic consumption of refined carbohydrates between meals was associated with poorer 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 efficiently digest a particular type of food. Because of 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 Westerners, a significant dietary change occurred in the second half of the 20th centuryth century, when industrialized foods began to become common. These foods often contained high concentrations of refined carbohydrates—primary sucrose, fiber-depleted gelatinous starch, high-sugar corn syrup, and others.
This dietary change was associated with an increase in the incidence of obesity, type II diabetes, cardiovascular disease, caries, hypertension and many other diseases. The physiological mechanisms involved in the development of these diseases are now believed to involve repeated excessive concentrations of glucose (hyperglycemia) and insulin (hyperinsulinemia) in the bloodstream accompanied by cells becoming less sensitive to the effects of insulin (insulin resistance ). Glucose is a simple sugar that is the primary source of energy in our body, while insulin is a hormone that facilitates the uptake of glucose into the cells.
Study author Leonard Guillou and his colleagues wanted to investigate whether the consumption of refined carbohydrates affects cognition in healthy young adults. They noted that studies of the long-term effects of carbohydrate consumption have so far been mostly conducted on older individuals and in the context of certain diseases. Data on the effects of chronic consumption of refined carbohydrates on young, healthy adults are lacking. They organized an experiment.
Participants were 95 healthy young adults between the ages of 20 and 30, 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 sugar levels. Participants then completed a cognitive assessment test (Wechsler’s Digit Symbol Substitution Cognitive Test). They were then served one of two types of breakfast.
Each type of breakfast contained 500 kilocalories, but one was composed of unrefined carbohydrates (whole grain bread, butter, cheese, a raw fruit and an unsweetened drink) and the other of refined carbohydrates (French baguette from industrially ground flour, jam, fruit juice and an unsweetened drink with sugar available).
The breakfast to be served was randomly selected each day. After breakfast, participants completed questionnaires about their demographic characteristics, physical activity levels, and dietary habits. One and a half hours after breakfast, the participants’ blood sugar levels were measured again and they completed another cognitive assessment (Wechsler cognitive test). Between these steps, researchers measured participants’ height and weight.
The results showed that 40% of men and 54% of women ate afternoon snacks (equivalent to Afternoon tea, 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 poorer cognitive performance.
A similar but weaker relationship 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 BMI values tended to perform worse on the cognitive assessments.
“The recent western dietary change, characterized mainly by the massive increase in the consumption of refined carbohydrates, has well-known harmful consequences for health. “Given the increasing number of people affected by these pathologies and the repeated failures of many medical treatments, our study reinforces the belief that the most promising research should focus on prevention in healthy individuals,” the study authors concluded.
The study makes a valuable contribution to the scientific knowledge of connections between dietary choices and cognitive performance. However, it should be noted that the study design does not permit 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 poorer tend to eat lots of refined carbohydrates between meals. These are not the only possibilities.
The study, “Chronic Refined Carbohydrate Consumption as Measured by Glycemic Load and Variation in Cognitive Performance in Healthy Humans,” was authored by Leonard Guillou, Valerie Durand, Michel Raymond and Claire Berticat.