Changes in the immune system explain why belly fat is bad for thinking

December 17, 2019

Science Daily/Iowa State University

Researchers have found for the first time that less muscle and more body fat may affect how flexible our thinking gets as we become older, and changes in parts of the immune system could be responsible.

These findings could lead to new treatments that help maintain mental flexibility in aging adults with obesity, sedentary lifestyles, or muscle loss that naturally happens with aging.

The study, led by Auriel Willette, assistant professor of food science and human nutrition, and Brandon Klinedinst, a PhD student in neuroscience, looked at data from more than 4,000 middle-aged to older UK Biobank participants, both men and women. The researchers examined direct measurements of lean muscle mass, abdominal fat, and subcutaneous fat, and how they were related to changes in fluid intelligence over six years.

Willette and Klinedinst discovered people mostly in their 40s and 50s who had higher amounts of fat in their mid-section had worse fluid intelligence as they got older. Greater muscle mass, by contrast, appeared to be a protective factor. These relationships stayed the same even after taking into account chronological age, level of education, and socioeconomic status.

"Chronological age doesn't seem to be a factor in fluid intelligence decreasing over time," Willette said. "It appears to be biological age, which here is the amount of fat and muscle."

Generally, people begin to gain fat and lose lean muscle once they hit middle age, a trend that continues as they get older. To overcome this, implementing exercise routines to maintain lean muscle becomes more important. Klinedinst said exercising, especially resistance training, is essential for middle-aged women, who naturally tend to have less muscle mass than men.

The study also looked at whether or not changes in immune system activity could explain links between fat or muscle and fluid intelligence. Previous studies have shown that people with a higher body mass index (BMI) have more immune system activity in their blood, which activates the immune system in the brain and causes problems with cognition. BMI only takes into account total body mass, so it has not been clear whether fat, muscle, or both jump-start the immune system.

In this study, in women, the entire link between more abdominal fat and worse fluid intelligence was explained by changes in two types of white blood cells: lymphocytes and eosinophils. In men, a completely different type of white blood cell, basophils, explained roughly half of the fat and fluid intelligence link. While muscle mass was protective, the immune system did not seem to play a role.

While the study found correlations between body fat and decreased fluid intelligence, it is unknown at this time if it could increase the risk of Alzheimer's disease.

"Further studies would be needed to see if people with less muscle mass and more fat mass are more likely to develop Alzheimer's disease, and what the role of the immune system is," Klinedinst said.

Starting a New Year's resolution now to work out more and eat healthier may be a good idea, not only for your overall health, but to maintain healthy brain function.

"If you eat alright and do at least brisk walking some of the time, it might help you with mentally staying quick on your feet," Willette said.

https://www.sciencedaily.com/releases/2019/12/191217141531.htm

Measure of belly fat in older adults is linked with cognitive impairment

August 1, 2018

Science Daily/Trinity College Dublin

Data from over 5,000 adults over the age of 60 indicates that as waist:hip ratio increases, so does cognitive impairment. The findings have significant implications as the global prevalence of dementia is predicted to increase from 24.3 million in 2001 to 81.1 million by 2040.

Previous studies have found that people who are overweight do not perform as well on tests of memory and visuospatial ability compared to those who are normal weight. However, it is not well known if this is true in older adults. This is of concern within Ireland, as over half of the over 50s population is classified as being centrally obese, with only 16% of men and 26% of women reported to have a BMI (body mass index) within the normal range.

The researchers used data from the Trinity Ulster Department of Agriculture (TUDA) ageing cohort study comprising, which is a cross-border collaborative research project gathering data from thousands of elderly adults in Northern Ireland and Ireland.

The researchers found that a higher waist:hip ratio was associated with reduced cognitive function. This could be explained by an increased secretion of inflammatory markers by belly fat, which has been previously associated with a higher risk of impaired cognition. On the contrary, body mass index (BMI) was found to protect cognitive function. BMI is a crude measure of body fat and cannot differentiate between fat and fat-free mass (muscle), thus it is proposed that the fat-free mass component is likely to be the protective factor.

To the best of the authors' knowledge, this is one of the largest studies of older adults to report these findings. Given the high prevalence of overweight and obesity in the older population and the economic and social burden of cognitive dysfunction, the results suggest that reducing obesity and exposure to obeso-genic risk factors could offer a cost-effective public health strategy for the prevention of cognitive decline.

Clinical Associate Professor in Medical Gerontology at Trinity, Conal Cunningham, is the senior author of the study. He said: "While we have known for some time that obesity is associated with negative health consequences our study adds to emerging evidence suggesting that obesity and where we deposit our excess weight could influence our brain health. This has significant public health implications."

https://www.sciencedaily.com/releases/2018/08/180801115257.htm