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Loss of olfactory system function – the sense of smell – is an early indicator of cognitive decline in people with type 2 diabetes and obesity. A new study in mice demonstrates the negative effects of a high-fat, high-sugar Western dietary pattern on odor-related learning and memory.

Smell is an important regulator of behavior and memory, especially in non-human animals like mice. Olfactory system dysfunction may be due to decreased neurogenesis in the olfactory regions of the brains. In this way, changes in smell may signal decreased neurogenesis in other areas of the brain, which may indicate cognitive decline and Alzheimer’s disease progression.

The investigators fed mice either standard chow, a high-fat diet (54 percent of calories from fat), or a Western diet (42 percent of calories from fat, 34 percent of calories from sugar) for eight months. They measured body weight, blood glucose, olfactory learning and memory, and cellular mechanisms of smell.

After just three months of consuming a Western diet, mice showed declines in odor-related learning and memory. Weight gain and loss of glucose control were similar between the mice eating the Western and high-fat diets, but higher than among the mice eating the standard chow. After eight months, the mice consuming the Western and high-fat diets exhibited a diminished sense of smell and impaired olfactory learning and memory. However, the authors were unable to detect cellular changes related to this outcome.

These findings add to a growing number of studies investigating the role of diet and obesity in cognitive decline. The authors encourage future researchers to investigate the interactions between olfactory and endocrine systems in people with obesity and type 2 diabetes.

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