August 8, 2025, 10:45 am | Read time: 4 minutes
Exception with Consequences? According to British researchers from the University of South Wales, even a single serving of fast food can negatively affect the brain. FITBOOK author Friederike Ostermeyer explains what the results of their latest study mean and whether you should now avoid your occasional favorite burger.
Junk food like a whole pizza or a burger with fries is full of saturated fats. It’s well-known that these are harmful to the cardiovascular system over time. But what about the immediate effects of a single fast-food meal on the brain? British researchers have tackled this question and found an insightful result in their study. It was particularly evident that the brains of older people are especially sensitive to an extremely fatty meal. The study was recently published in the journal “The Journal of Nutritional Physiology.”1
41 Healthy Men Given Milkshake with 130 Grams of Fat
The researchers recruited 20 young men aged 18 to 35 and 21 men aged 60 to 80. The following parameters were measured in the fasting state:
- Blood tests for triglycerides, glucose, and insulin
- Systemic vascular function (indicating how well the arteries can dilate with slowed blood flow)
- Dynamic cerebral autoregulation (the brain’s ability to maintain stable blood flow despite fluctuations in blood pressure)
All participants were then given a test meal. The researchers chose a cream milkshake, which they called “the brain bomb.” The drink contained 1,362 calories and 130 grams of fat, roughly equivalent to the fat content of an average fast-food meal.
How Fast Food Weakens Brain Function
Four hours later, the researchers measured the same parameters again. As expected, blood fats (triglycerides), glucose, and insulin levels rose significantly in all participants. The blood vessels became stiffer and lost their ability to relax and expand. This confirmed the results of previous studies, which found that an extremely high-fat meal negatively affects blood vessels associated with heart health. The new finding: This effect simultaneously reduced the brain’s ability to compensate for blood pressure fluctuations. In older adults, the impact was about ten percent more pronounced.
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Why Unstable Blood Supply to the Brain Is Problematic
Normally, the body has a mechanism that ensures a stable blood supply to the brain. This is important for everyday blood pressure fluctuations, such as those caused by exercise or getting up in the morning. You can think of it as a “built-in shock absorber.” However, a single fatty fast-food meal is enough to weaken this mechanism. This can lead to too little or too much blood reaching the brain temporarily. In an accompanying article on the science portal “The Conversation,” the researchers speculate that this increases the risk of conditions like stroke and dementia. 2
Is Fast Food Already Harmful as an Exception? Here’s What the Study Leader Says
Many health-conscious people occasionally indulge in junk food as an exception. Should you avoid it? FITBOOK asked study leader Dr. Chris Marley. His assessment: “An occasional high-fat fast-food meal is very unlikely to cause harm, even if it temporarily negatively affects the brain.” The study rather emphasizes the importance of focusing on polyunsaturated fats in daily nutrition—especially for older individuals. These are found in fatty fish, nuts, and seeds. And if the craving for junk food is too strong, Marley advises: “Consider which healthier version of your favorite fast food is available. Try to reduce the fat and salt content as much as possible. Alternatively, choose a smaller portion that can be just as satisfying but less taxing on the body.”
Limitations of the Study
Incidentally, the researchers did not give their participants any cognitive tasks after the fat shake. Therefore, it remains unclear whether and how fast food and the like immediately affect brain performance. It also remains unclear how the female brain reacts to a high-fat fast-food meal. According to the researchers, this is a crucial knowledge gap, as women are at a higher risk of stroke and dementia later in life than men.