A groundbreaking study conducted by a group of French researchers and published in Personality and Individual Differences in May 2023 has shed light on the impact of refined carbohydrates on cognitive function. The findings reveal that these commonly consumed carbohydrates may have a negative effect on cognitive performance, leading some to suggest that they might actually make people less intelligent.

The study focused on a cohort of 95 healthy young adults aged between 20 and 30, comprising 48 women and 47 men. The researchers meticulously analyzed the relationship between refined carbohydrate consumption and cognitive performance in this group. The results showed a clear and concerning trend: regardless of gender, the consumption of food containing refined carbs had a detrimental impact on cognitive function. The researchers went on to highlight that the consumption of foods with a high glycemic index (GI) was particularly associated with decreased cognitive performance.

In their paper, the researchers emphasized the significant shift in dietary habits that occurred in the Western world during the latter half of the 20th century. This shift witnessed a substantial increase in the consumption of refined carbohydrates, which, in turn, resulted in various adverse health effects. Industrialized food production introduced a plethora of highly processed refined products that quickly found their way into the everyday diets of millions.

Carbohydrates, as a primary source of fuel for the brain, are essential for supporting cognitive function. However, not all carbohydrates are created equal. Whole carbs, found in unprocessed foods and containing natural fiber, vitamins, and minerals, offer more substantial health benefits. In contrast, refined carbs, often referred to as "empty" calories, have been stripped of most of their nutritional value through the refining process. Common examples of refined carbs include breakfast cereals, pasta, pastries, pizza dough, sweet desserts, and white bread, among others.

Interestingly, the negative impact of refined carbohydrates extends beyond cognitive function, as they have been linked to mental health issues as well. An August 2015 study published in the American Journal of Clinical Nutrition (AJCN) delved into this aspect. Led by Dr. James Gangwisch from Columbia University Medical Center's Department of Psychiatry, the study examined data from over 70,000 post-menopausal women participating in the Women’s Health Initiative Observational Study, conducted by the National Institutes of Health between 1994 and 1998.

The researchers analyzed depression rates alongside the types of carbohydrates consumed and the glycemic index of the foods. They discovered that eating carbohydrates leads to varying degrees of increased blood sugar levels, depending on the type of carb ingested. The study found that the higher the refined nature of the carbohydrate, the higher its score on the glycemic index, which ranges from zero to 100.

The glycemic index essentially measures the amount of sugar present in the blood after eating. Consequently, the researchers observed that higher dietary glycemic index scores, resulting from the consumption of added sugars and refined grains, were associated with an increased risk of new-onset depression in post-menopausal women.

The mechanism behind this link lies in the hormonal response triggered by refined foods, such as white bread, white rice, and soda, which causes a reduction in blood sugar levels. This response can lead to mood changes, fatigue, and other symptoms associated with depression.

Furthermore, an animal study conducted by researchers from the Federal University of Minas Gerais in Brazil in July 2016 reinforced the effects of refined carbs on mental health. The study involved two groups of mice: one fed a standard diet and the other provided with a high amount of refined carbohydrates. Both groups were then subjected to three different stress tests. The results indicated that a moderate obesity induced by a high refined carbohydrate diet might facilitate the development of anxiety and depressive-like behaviors after experiencing stress.