Eating a balanced diet is tricky at the best of times. When we’re stressed, sleep-deprived, or emotional, it’s even easier to reach for convenient, but fatty, foods.
Unfortunately, high-fat diets are linked to obesity, diabetes, cardiovascular diseases, and other health problems. High-fat diets can also cause poor sleep.
Prince Peter Wormenor, a graduate student in the Department of Zoology and Physiology, wanted to understand how high-fat diets and their accompanying sleep disruptions change the brain. Specifically, he examined the prefrontal cortex, the part of the brain responsible for regulating emotions, learning, and cognition.
If high-fat diets influence the prefrontal cortex, they might create a vicious cycle: the diet disturbs one’s sleep, which makes it more difficult to regulate emotions or think clearly, which then leads to impulsive decisions—such as eating more high-fat foods.
Unhealthy neurons before bed
Wormenor set up an experiment where some mice were fed a normal diet and others were fed a high-fat diet for one week. Wormenor used light boxes to create different “time zones”—half of the mice were experiencing evening lighting conditions when he examined them, while the other half were exposed to morning conditions.
After a week, Wormenor looked at individual neurons in each mouse’s prefrontal cortex, examining key indicators of neuron health and function.
Neurons from male mice fed high-fat diets showed indications of poor health when they were waking up. However, neurons examined right before the mice fell asleep were even less healthy than neurons examined when the mice woke up.
Typically, a mouse’s neurons are less excitable as the mouse goes to sleep in comparison to when the mouse is fully awake. Wormenor found that male mice fed a high-fat diet had significantly more neuron activity when they were going to sleep than male mice fed a normal diet.
“Consumption of a high-fat diet in itself is not a good thing, but you can have a more adverse effect at a particular time of day than at another time of day,” says Wormenor. In other words, eating bacon might make it harder to think throughout the day, but it may have more of an impact on your brain when you’re going to bed than when you’re waking up.
In contrast, whether they were tested in the morning or evening, female mice who were fed a high-fat diet had similar neural health to female mice who ate a normal diet. While it’s possible that diet changes might eventually impact female mice, no significant changes were observed after one week.
Breaking the vicious cycle
Though this study was focused on short-term consequences of a high-fat diet on the prefrontal cortex, Wormenor’s research could have implications for the entire brain. “When one region is affected or influenced negatively, you would expect a change in the way other regions are impacted also,” says Wormenor.
Ultimately, Wormenor’s findings might help researchers develop behavioral interventions that give people more tools to break the vicious cycle of poor dietary habits and poor sleep. If decision-making is most compromised in the evening, figuring out strategies to avoid eating at night might help people who struggle with their diets. Changing when we eat might make it easier to regulate emotions and sleep—and pick different foods next time.
This article was originally published in the 2025 issue of Reflections, the annual research magazine published by the UW College of Agriculture, Life Sciences and Natural Resources.
PHOTO: Overhead view of a large group of food with high content of dietary fiber arranged side by side. The composition includes berries, oranges, avocado, chia seeds, wholegrain bread, wholegrain pasta, whole wheat, potatoes, oat, corn, mixed beans, brazil nut, sunflower seeds, pumpkin seeds, broccoli, pistachio, banana among others. (Photo: iStock – fcafotodigital)
