In the past few years, researchers have increasingly been suspecting a link between Alzheimer’s and chronic obesity; it’s always hard to draw clear causation between diets and diseases, but the more obesity becomes prevalent, the more it is being linked to brain conditions. In the new study, researchers have established a clear link between mice fed a high-fat diet for 30 weeks and a subsequent deterioration in their cognitive abilities. The obesity resulted in diabetes and triggered symptoms such as anxiety and depression, and worsened existing Alzheimer’s disease.

“Obesity and diabetes impair the central nervous system, exacerbating psychiatric disorders and cognitive decline. We demonstrated this in our study with mice,” says Larisa Bobrovskaya, assistant professor at the University of South Australia and study author.

Bobrovskaya and colleagues split mice into two groups: one that was fed a normal diet, and one that was fed a high-fat diet for 30 weeks. Their body weight, food intake, and blood sugar were analyzed regularly. Also, insulin tolerance and cognitive dysfunction were measured at different intervals.

Unsurprisingly, the mice who ate a high-fat diet gained a lot of weight — but that was just the start of it. They started behaving abnormally, showed decreased cognitive function, and also had pathological changes in the brain (their brains got smaller).

“Obese individuals have about a 55% increased risk of developing depression, and diabetes will double that risk,” Bobrovskaya says. “Our findings underline the importance of addressing the global obesity epidemic. A combination of obesity, age, and diabetes is very likely to lead to a decline in cognitive abilities, Alzheimer’s disease, and other mental health disorders.”

Ultimately, it’s hard to replicate the same type of study in humans (because you can’t feed humans a diet you know is bad for them just to see what happens), but the evidence is piling up linking obesity (and a high-fat diet, in particular) to impaired memory and to brain conditions. So far, there is no definitive evidence that eating or avoiding a specific food can prevent Alzheimer’s disease or age-related cognitive decline. However, there does seem to be a link between diet and Alzheimer’s, although researchers just haven’t narrowed it down fully. For instance, the Mediterranean and Mediterranean-DASH diets have been linked to lower rates of Alzheimer’s and studies such as this one, on mice, suggest that a diet high in fats is bad for the brain.

Journal Reference: Jing Xiong et al, Long term high-fat diet induces metabolic disorders and aggravates behavioral disorders and cognitive deficits in MAPT P301L transgenic mice, Metabolic Brain Disease (2022). DOI: 10.1007/s11011-022-01029-x