When you’re in a rough spot, there’s nothing quite like a bag of hot chips (fries if you live in the U.S). Or fried chicken. Or pizza fresh from the oven. We all know that comfort eating isn’t exactly good for our health, but at least it helps deal with stress, right? Unfortunately, that’s not what researchers from the University of Birmingham have found – at least, not in the case of high-fat meals, which is what most comfort foods are.
The researchers recruited 21 healthy adults aged 20-30 and randomly assigned them to eat either a high-fat meal containing 56.5 grams of fat, or a low-fat meal containing 11.4 grams of fat. Both meals had the same number of calories. An hour and a half later, participants all took a mental stress test called the Paced-Auditory-Serial-Addition-Task, or PASAT. In this test, participants are presented with a number every 3 seconds and must add the number they just heard to the one that preceded it. I know. Few things are more stressful than mental maths.
Researchers measured cardiovascular parameters like blood pressure at various points during the study, as well as the oxygenation of the prefrontal cortex, a region of the brain involved in executive functions such as planning and decision making. Then the experiment was then repeated, but the low fat group and the high fat group swapped places.
There was no significant difference in participants’ performance in the PASAT test between the high-fat and low-fat groups. There was also no significant difference in perceived stress – both groups reported finding the test similarly stressful and challenging. Both groups experienced similar cardiovascular changes during the test, such as a rise in blood pressure and heart rate.
What differed significantly, however, was was cerebrovascular response. Researchers found that oxygenation of the prefrontal cortex significantly increased during during the stress test in participants who consumed a low-fat meal, but not in those who consumed a high-fat meal, suggesting that this meal prevented blood flow to the prefrontal cortex from being increased. However, when researchers looked at blood flow in the carotid arteries (the arteries that supply the brain with blood) they found that blood flow increased in both groups, with no significant difference between the high-fat and low-fat meals.
Finally, the researchers found that people in the high-fat group had significantly higher (worse) mood disturbance scores following following the meal and immediately after the stress. This score is an amalgamation of different self-reported mood scores. In particular, participants in the high-fat group reported feeling more fatigued than the other group.
According to this study, eating fatty foods does not seem to affect a person’s perception of stress, for good or for bad. However, it does seem to worsen their mood, and also has a measurable effect on the brain: preventing an increase in oxygenation in response to stress. The function of the prefrontal cortex already decreases under stressful conditions, which is one of the reasons stressed humans make worse decisions and have poorer self control. It’s quite possible that reduced blood supply (upon which the brain is very dependent) makes the cognitive effects of stress worse after eating fatty comfort food.
Since fatty foods didn’t appear to affect blood flow to the brain as a whole, one possible explanation is that higher levels of fatty acids in the blood change the way blood flow within the brain is distributed. Usually, highly active brain regions produce some lactic acid, which is a waste product of breaking down sugar when insufficient oxygen is available. This lactic acid is released into the blood and causes blood vessels to dilate, increasing oxygen supply. The authors propose that fatty acids could be interfering with this mechanism, which would explain why blood supply (and therefore oxygenation) only seemed to increase after stress in the low-fat group.
More research is going to be needed to figure out exactly what’s going on. There are currently very few studies looking at the effects of fatty diets on stress. One could argue that the conditions of these studies do not really represent real life chronic comfort eating, which often happens under conditions of long-term stressful conditions. For the moment, though, it certainly seems as though typical fatty comfort foods do not actually comfort you and may actually impair both mood and cognitive performance.
Fat Consumption Attenuates Cortical Oxygenation during Mental Stress in Young Healthy Adults https://doi.org/10.3390/nu15183969
Title image by Louis Hansel, Upslash