Your Brain on Junk Food
In healthy individuals, insulin in the brain acts as an appetite suppressant. During insulin resistance, brain insulin no longer properly regulates food intake or metabolism. Prior research shows that disruption of brain insulin responsiveness promotes metabolic and neurodegenerative diseases.
Researchers were interested in how quickly brain insulin responsiveness could be impacted by junk food. They investigated the impact of a 5-day high calorie diet on insulin sensitivity and body fat composition.
For this study, 29 men (age 19-27) of average weight were split into 2 groups. For 5 days in a row, half the participants added 1,500 calories of ultra-processed high calorie snacks to their regular diet. The control group did not consume extra calories.
Researchers collected MRI data to examine the liver’s fat content and the brain’s insulin sensitivity at baseline, at the end of the 5-day high calorie intake period, and again a week after the junk food intake. They discovered:
The fat content of the liver increased for the calorie supplemented group after just 5 days of high processed high calorie snacks
The significantly lower insulin sensitivity in the brain in the junk food supplemented group, compared to the control group, also persisted one week after returning to a normal diet. This effect had previously only been observed in obese individuals.
The researchers theorize that disruption in brain insulin action by the overconsumption of junk food may initiate weight gain, even if overeating of ultra-processed food is short term. This can increase the risk of obesity and disease.
Takeaway: Short-term overeating of high calorie ultra-processed food can trigger liver fat accumulation and brain insulin disruption that outlasts the timeframe of overconsumption. Junk food is harmful to normal brain insulin action.
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Source
Stephanie Kullman, et al., A short-term, high-caloric diet has prolonged effects on brain insulin action in men | Nature Metabolism, Feb. 21, 2025.
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