Image: Classic Hamburger Sandwich
Image courtesy: KEKO64 at FreeDigitalPhotos.net

 

Research funded by the ARC Discovery Projects scheme, and conducted at Macquarie University, has shown that Western-style diets, high in saturated fats and added sugar, can disrupt aspects of cognition in adults. This disrupted cognition impairs food intake control, causing overeating, contributing to the rise of obesity in Western countries.

Chief Investigator, Professor Richard Stevenson, was granted $307,000 in 2015 to investigate whether cognitive impairments occurred in people consuming Western-style diets and if so, to what extent. His most recent results were presented at the annual meeting of the Society for the Study of Ingestive Behaviour in early July.

Professor Stevenson explained that memory inhibition, impaired olfactory perception and impaired interoception—the ability to perceive internal bodily states such as hunger and fullness—all contribute to the tendency to overeat.

“A Western-style diet appears to subtly impair a part of the brain called the hippocampus. Normally, when we are full after a meal, seeing more food does not make us want to eat. This may be because the body’s state of being full leads to the hippocampus inhibiting memories of how nice it might be to eat that food. If the hippocampus is impaired, it is probably less efficient at inhibiting those memories, so you look at that food and all those pleasant memories of how nice it was to eat come flooding back, making it harder to resist eating.”

Professor Stevenson’s research investigated impaired food intake control in healthy, lean people. Participants were selected based on a dietary intake questionnaire. They rated their liking and wanting of snack foods before and after eating a full meal, and underwent memory and learning tests targeted to the hippocampus.

“We chose to study lean, healthy people deliberately, so that we can see whether any diet-related changes to the brain precede weight gain and its medical consequences. There is already evidence that diet has a similar effect on children, and cognitive impairments are already well documented in the obese.”

The tests of hippocampal function generally employed pictures, words and stories that did not relate to food. For example, participants were asked to listen to a story and then asked to recount it from memory after a delay of around 20 minutes. Results showed that memory performance and snack food desires were linked.

“Findings of poorer episodic memory in consumers of a Western-style diet—which is what these tests measure—is highly relevant to everyday life. It is the part of the brain you use when you are asked what you had for breakfast or what you watched on TV last night.”

Professor Stevenson concluded that people who consume Western-style diets seem to become less sensitive to internal signals of hunger and fullness and it takes more food for them to feel full. This is most likely due to poor diet subtly disrupting the brain’s ability to regulate food intake. 

“These results will help us to understand why people gradually gain weight over many years, becoming overweight and then in the much longer term, obese. If we can understand how this happens, we may be able to stop it.”