Is Your Belly Fat Fogging Your Thinking?

Almost one-third of the global population is classified as being overweight or obese. Because obesity increases the risk of several age-related conditions, including cardiovascular disease, brain atrophy, and Alzheimer's disease, it is important to be able to quantify what is meant by obesity and investigate the mechanisms that link body fat to accelerated aging.

Today, various measures are being used to quantify obesity: body mass index (BMI) is thought to estimate fat stored peripherally, whereas waist-to-hip ratio (WHR) and waist circumference (WC) are indicative of fat located viscerally around the various organs of the body. It is now believed that visceral fat constitutes a much greater risk factor for heart disease and brain atrophy. This is why BMI tends to be a less useful indicator of overall health.

A recent study examined the associations of BMI, WHR WC, and physical activity with cerebral blood flow into the brain, specifically the grey matter in 495 older adults around 69 years old.

Participants self-monitored their typical time-per-day spent doing moderate- or vigorous-intensity physical activities and were then classified as having "low," "moderate," or "high" physical activity levels.

The study discovered that an increase in BMI of 0.43, WHR of 0.01, or WC of 1.3 cm were associated with the same reduction in cerebral blood flow as seen with one year of advancing age. In addition, subjects who met the criteria of being overweight had significantly lower cerebral blood flow overall.

For subjects who were overweight according to BMI or WHR/WC ratios, high levels of physical activity reduced the statistical association with reduced cerebral blood flow but had no effect on total cerebral blood flow. The authors speculated that physical activity might help by slowing down the accumulation of visceral fat thus reducing the level of systemic inflammation.

Fat cells produce inflammation by releasing proteins called cytokines. The more fat cells you have, the more cytokines get released into your blood and brain. Essentially, obesity is associated with chronic, body-wide inflammation that slow shrinks brain regions that are used for learning new things and recalling memories.

Another recent study examined the relationships between academic performance and BMI among 2,519 young people. BMI was inversely correlated with general mental ability, even after controlling for demographics, lifestyle factors, and lipid profiles. Overall, obesity is implicated in lower performance on cognitive control tasks. The longer the inflammation is present, the more brain shrinkage occurs. This may explain why elderly obese people have more impaired learning and memory abilities than elderly thin people.

In summary, as BMI, WHR, and waist size increased, the elderly subjects showed a reduction in cerebral blood flow. Age-related reductions in cerebral blood flow were correlated with very small increases in waist size. High levels of physical activity produced only a modest benefit in cerebral blood flow.