Emerging research has found that a high-fat diet can impair cognitive function. A study conducted by a group of neuroscientists at the University of South Australia found a definitive association between a high-fat diet and the development of mental health disorders such as depression, anxiety, and the worsening of Alzheimer's disease or dementia in mice. 

They also found that their test subjects with impaired cognitive ability were more likely to make poor health choices and ruin their metabolism due to these brain changes. Yet, how exactly does a high-fat diet impair cognitive function?  

The Link Between Obesity and Cognitive Function 

In a UK-based research study, about 12,000 participants between 45 and 76 years old and with varying measures of BMI, waist-to-hip ratios, and total fat mass underwent brain imaging tests. The results showed that individuals with a higher body mass index had different brain scans than those with a BMI in the "healthy" category. 

Researchers discovered that the link between brain volume and obesity reduced the gray matter in the brain. 

Gray matter makes up the brain's outer layer and is where information is processed. It plays a role in normal human functions such as motor control, coordination and balance, memory, and emotional regulation. As the gray matter begins to shrink, individuals risk developing cognitive disorders, memory loss, and declining motor skills. 

Similarly, this study also found a link between brain volume and obesity related to white matter in the brain. White matter sits within the deeper parts of the brain and helps with learning. 

This link between brain volume and obesity was more significant in men than women. Obese men were at a higher risk of experiencing shrinking in the gray and white matter, while women only experienced shrinkage in the brain's white matter. 

These discoveries coincided with previous research that proved a high body mass index was associated with a smaller brain volume. Yet, despite evidence pointing to the link between brain volume and obesity, researchers are still unclear about the exact causes. Some experts believe there is a reduction in white and gray matter in the brain due to inflammation caused by increased body fat. This inflammation harms brain tissue, resulting in a loss of neurons, affecting cognitive function. 

Yet, still, it is "unclear if obesity changes the brain or if people with lower volumes of gray matter are at a higher risk of obesity."

How a High-Fat Diet can Impair Cognitive Function 

With an understanding of how obesity affects brain size and structure, a correlation can be made between a high-fat diet and cognitive decline. Many overweight and obese individuals follow an unhealthy, high-fat diet that contributes to their obesity. The international study led by UniSA neuroscientists found that the mice on a high-fat diet had an increased body fat percentage and elevated glucose levels. 

We know that prolonged high blood sugar levels can lead to insulin resistance, which can cause diabetes. Diabetes is known to "impair the central nervous system, exacerbating psychiatric disorders and cognitive decline," which was demonstrated in the study as cited by Associate Professor Larisa Bobrovskaya. 

Similarly, another study further expanded evidence that suggests a high-fat diet can impair cognitive function, specifically increasing the risk of dementia. "In human epidemiological studies, it has been shown that intake of a high-fat diet that includes mostly omega-6 and saturated fats is associated with worse performance on a cognitive task."

The exact mechanism for causing impaired cognitive function is unknown. Still, it is believed to be a combination of oxidative stress, insulin resistance, inflammation in the brain and hippocampus, reduced rates of vascularization, and altered membrane functioning. 

How to Prevent Brain Damage 

Although a high-fat diet can impair cognitive function, it can be managed. Older individuals are most at risk of increasing their chances of developing dementia, Alzheimer's disease, or other mental health conditions. Yet, the good news is that a low-fat diet can prevent the deterioration of cognitive function.