A recent study reveals that even a short period of consuming ultra-processed foods can durably alter brain activity. These changes, observed in healthy men, resemble those typically associated with obesity.
The study, published in
Nature Metabolism, shows that five days of a diet high in fats and sugars are enough to modify the brain's response to insulin, a key hormone in appetite and metabolism regulation. These findings raise questions about the long-term effects of dietary habits, even in the absence of weight gain.
Immediate effects on the brain
Researchers recruited 29 healthy young men, 18 of whom followed a high-calorie diet for five days. This diet included snacks rich in fats and sugars, such as chocolate bars and chips. Despite an average increase of 1,200 calories per day, their weight remained stable.
Brain imaging revealed increased activity in areas related to food reward. These brain changes, similar to those observed in obese individuals, suggest that the brain quickly adapts to an unbalanced diet.
One week after the end of the diet, certain brain areas related to memory and cognition still showed reduced sensitivity to insulin. This persistence of effects highlights the brain's ability to retain traces of poor nutrition, even after returning to a normal diet.
Health implications
The study sheds light on a link between the consumption of ultra-processed foods and the accumulation of fat in the liver. In five days, the participants' liver fat content increased significantly, a risk factor for metabolic diseases like type 2 diabetes.
Researchers also observed disruptions in the brain's reward processing. Participants showed reduced sensitivity to rewards and an increased reaction to punishments, a pattern often associated with obesity. These changes could promote unhealthy eating behaviors in the long term.
Finally, the study emphasizes that these brain alterations occur before any visible weight gain. This suggests that the brain could play a key role in the development of obesity and associated diseases, independent of physical changes.
To go further: What is insulin resistance?
Insulin resistance is a physiological phenomenon where the body's cells respond less effectively to insulin, a hormone produced by the pancreas. Normally, insulin helps regulate blood sugar by allowing cells to absorb glucose from the blood. When this resistance sets in, glucose accumulates in the blood, which can lead to prediabetes or type 2 diabetes.
In the brain, insulin plays a role in appetite and metabolism regulation. It sends satiety signals to indicate that we have eaten enough. However, in cases of insulin resistance, these signals are disrupted, which can lead to overeating and weight gain.
Insulin resistance is often linked to factors such as a diet high in sugars and fats, a sedentary lifestyle, or genetic predisposition. It is also associated with conditions like obesity, metabolic syndrome, and certain cardiovascular diseases. Understanding this mechanism is essential for preventing and treating these health disorders.
How do ultra-processed foods affect the liver?
Ultra-processed foods, rich in added sugars, saturated fats, and chemical additives, have a significant impact on liver health. When consumed in excess, these foods can lead to a rapid accumulation of fat in the liver, a phenomenon called non-alcoholic fatty liver disease. This condition, often asymptomatic at first, can progress to more serious problems like liver inflammation (steatohepatitis) or cirrhosis.
The liver plays a central role in nutrient metabolism. When overwhelmed by an excess of sugars and fats, it stores these surpluses as triglycerides, increasing liver fat content. This accumulation disrupts the liver's normal functioning, reducing its ability to regulate blood sugar and eliminate toxins.
In the long term, excessive consumption of ultra-processed foods can also promote the development of insulin resistance, a major risk factor for type 2 diabetes. Moreover, fatty liver is often associated with cardiovascular diseases and an increased risk of metabolic complications. Adopting a balanced diet and limiting ultra-processed products are therefore key measures to preserve liver health.
Article author: Cédric DEPOND