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Carbs Between Meals Decreases Brain Performance

A study in France has revealed that worse cognitive performance is associated with chronic consumption of refined carbohydrates between meals.

This effect remains consistent even when controlling for factors such as energy intake. The study’s findings were published in Personality and Individual Differences.

A specific diet is adapted by each animal species, with their digestive processes specialized to effectively digest a particular type of food. Consequently, sudden changes in their diet often result in health problems as their digestive system is not accustomed to the new food types.

In the latter half of the 20th century, most Western individuals experienced a significant shift in their diet due to the prevalence of industrialized foods. These foods frequently contained high concentrations of refined carbohydrates, including sucrose, fiber-depleted gelatinous starches, high sugar corn syrup, and others.

This dietary alteration coincided with an increase in the prevalence of obesity, type II diabetes, cardiovascular diseases, dental caries, hypertension, and numerous other illnesses. It is now believed that the physiological mechanisms underlying these diseases involve repeated exposure to excessive concentrations of glucose (hyperglycemia) and insulin (hyperinsulinemia) in the bloodstream, accompanied by reduced cellular responsiveness to insulin (insulin resistance). Glucose, a simple sugar and primary energy source in our bodies, is regulated by insulin, a hormone responsible for facilitating glucose uptake into cells.

Leonard Guillou, the study author, and his colleagues aimed to investigate whether the consumption of refined carbohydrates affects cognition in healthy young adults. They observed that previous studies examining the long-term effects of carbohydrate consumption primarily focused on older individuals or specific illnesses, lacking data on the effects of chronic consumption of refined carbohydrates on young, healthy adults. Therefore, they designed an experiment.

The experiment involved 95 healthy young adults aged between 20 and 30 years, who were recruited from the University of Montpellier in France. Participants arrived at the laboratory in groups of 3 or 4 in the early morning. The researchers initially measured their blood glucose levels, followed by a cognitive assessment test (Wechsler’s digit symbol substitution cognitive test). Subsequently, the participants were served one of two types of breakfast.

Each type of breakfast contained 500 kilocalories, but one consisted of non-refined carbohydrates (whole wheat bread, butter, cheese, a raw fruit, and a non-sweetened beverage), while the other comprised refined carbohydrates (French baguette made from industrially milled flour, jam, fruit juice, and a non-sweetened beverage with sugar added).

The breakfast to be served was chosen randomly each day. After breakfast, questionnaires regarding demographic characteristics, physical activity levels, and dietary habits were completed by the participants. An hour and a half after breakfast, their blood glucose levels were measured again, and another cognitive assessment (Wechsler cognitive test) was conducted. Height and weight measurements were taken by the researchers between these steps.

The results indicated that 40% of males and 54% of females engaged in afternoon snacking (corresponding to Le Goûter, a traditional afternoon snack or tea time). Additionally, 25% of both men and women consumed snacks between meals. Worse cognitive performance was associated with higher consumption of refined carbohydrates between meals and increased energy intake during the afternoon snack.

A similar, albeit weaker, association was observed for energy intake during breakfast. However, the cognitive performance was not associated with the breakfast consumed on the same day. Men with higher body mass index values tended to exhibit poorer performance on the cognitive assessments, but this trend was not observed among women.

The study authors concluded,

“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 individuals.”

While the study provides valuable insights into the connection between dietary choices and cognitive performance, it is important to note that the study design does not allow for definitive cause-and-effect conclusions. It is possible that higher consumption of refined carbohydrates between meals leads to decreased cognitive performance, but it could also be the case that individuals with poorer cognitive performance tend to consume more refined carbohydrates between meals. These are not the only potential explanations.


A massive diet switch has occurred in the occidental world since the second half of the 20th century, with a dramatic increase in refined carbohydrate consumption generating numerous deleterious health effects. Physiological mechanisms associated with refined carbohydrate consumption, such as hyperinsulinemia and insulin resistance, may impact cognition in healthy people before overt obesity, metabolic disease onset or dementia. To explore this possibility, the relationship between cognitive performance and chronic refined carbohydrate consumption was studied in healthy young adults (N = 95). Evaluation of chronic refined consumption was based on the glycemic load (a proxy of glycemic and insulinemic responses) of three mealtimes at higher glycemic risk: breakfast, afternoon snacking and between-meal snacking. Immediate consumption of refined carbohydrates was experimentally controlled. High chronic between-meal glycemic load is associated to a decrease of cognitive performance for men and women in the presence of several control variables, including energy intake. The different physiological ecologies of the three meals and the interpretation of the results in terms of adaptation or maladaptation to the modern dietary environment are discussed.

The study titled “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.