A new study suggests that a Western-style diet can impair hippocampal function and lead to a decreased ability to control one’s appetite. The findings were published in Royal Society Open Science.
A wealth of animal studies have found that animals fed a Western-style diet — a diet characterized by high intake of saturated fats and added sugars — display impaired hippocampal function and decreased appetitive control. Study authors Richard J. Stevenson and his team wanted to explore whether a similar effect would be found in humans.
As the researchers explain, while the hippocampus plays a major role in learning and memory, it is also associated with the regulation of appetite. Exactly how it controls appetite is unclear, but one theory suggests that the hippocampus makes use of internal bodily state (e.g., feeling sated) to modulate the difference between ‘liking’ a food item and ‘wanting’ a food item.
The authors explain how the hippocampus might react when faced with an excitatory food cue when feeling full. “Under such conditions, the hippocampus could either inhibit retrieval of associative networks connected with that food and/or dampen activation of brain areas mediating reward. If the hippocampus becomes impaired, then such regulation should become less efficient.”
An experimental study was conducted, involving a sample of healthy students who were currently following a nutritious diet (a diet scoring low on a validated measure of Western diet). On Day 1 of the study, the students, aged between 17 and 35, were assigned to one of two conditions that they would follow for the course of one week. The Western diet group was instructed to eat two Belgium waffles as a breakfast or dessert on four days, and to eat a main meal from a fast food chain (including a drink and dessert) on two other days. The control group was assigned to maintain their normal diet throughout the week.
Additionally, on Days 1 and 8 of the study, students were given breakfast in the lab. As a measure of appetitive control, all students completed a “wanting and liking” test, both before and after consuming breakfast. The test presented subjects with various snack foods and asks them to rate how much they liked and wanted the food items. By administering the test both before and after breakfast, researchers wanted to see whether subjects’ fullness would reduce their wanting ratings (indicating appetitive control). On Days 1 and 8, students also completed a verbal learning test, known to address hippocampal-dependent learning and memory (HDLM).
Results showed that, among those who followed the Western diet, wanting and liking ratings taken before breakfast were more similar to ratings taken after breakfast, on Day 8 compared to Day 1. In other words, on Day 8, these subjects showed a decreased ability to control their appetites when full, after a week of following a Western diet. Furthermore, the Western diet group performed worse on the verbal learning test than the control group.
Finally, researchers gave each participant an overall appetitive control score, based on their performances on the wanting and liking tests. Researchers then compared these scores to the learning test scores. It was found that a larger drop in test score was associated with a decrease in appetitive control. Importantly, this effect was only found amongst individuals in the Western diet group, and not the control group.
This finding suggests that a Western diet may influence appetitive control by impairing hippocampal function. The authors conclude, “More broadly, this experiment, alongside those from the other animal and human studies cited here, suggests that a WS-diet causes neurocognitive impairments following short-term exposure.”
The study, “Hippocampal-dependent appetitive control is impaired by experimental exposure to a Western-style diet”, was authored by Richard J. Stevenson, Heather M. Francis, Tuki Attuquayefio, Dolly Gupta, Martin R. Yeomans, Megan J. Oaten, and Terry Davidson.