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

Differences between male and female fat tissue, and health

Mouse study provides important clue as to how females stay healthier than males, even as body fat increases

October 23, 2018

Science Daily/York University

In a new study, researchers found that the abdominal fat on female mice had more blood vessels than the fat on male mice, and that this protected the health of the female mice as they gained fat from eating a high-fat diet.

Published today in Frontiers in Physiology -- Vascular Physiology, the research focuses on the differences between abdominal fat in obese male and female mice. A team of researchers under the direction of Professor Tara Haas found that the abdominal fat on female mice had more blood vessels than the fat on male mice, and that this protected the health of the female mice as they gained fat from eating a high-fat diet.

Males and females develop fat tissue differently and also differ in susceptibility to cardiovascular disease, insulin resistance and diabetes. However, the underlying biology behind why fat tissue in females is more protective against these conditions was not well understood, says Haas, a professor in the School of Kinesiology and Health Science, Faculty of Health.

Blood vessels are critical for maintaining healthy fat tissue by ensuring that the expanding fat cells are supplied with enough oxygen and nutrients, so the researchers looked at whether the abilities of the fat tissue to grow blood vessels and maintain healthy fat tissue would be different between males and females.

"We found that female mice have a higher number of blood vessels in their fat than males, and that females increase the number of blood vessels as they are fed a high fat diet, while males do not. We concluded that this response enabled females to maintain healthier fat and better insulin sensitivity," says Haas.

Martina Rudnicki, a York post-doctoral associate and first author of the study, pointed out that the study was unique because it focused on the differences in male and female fat tissue in the abdominal area. Although fat accumulates in different regions of the body, it is abdominal fat that is closely linked with increased risk of developing diabetes, particularly in males. So, the fact that females grow new blood vessels in this abdominal fat during weight gain may exert a health advantage for females.

The sex differences in the fundamental cellular processes that regulate the growth of blood vessels were unappreciated in the past, said Haas. It is important to understand them because they may contribute to an individual's susceptibility to develop serious obesity-related health complications such as diabetes, heart disease and cancer, ultimately impacting the health of more than 5.3 million Canadian adults.

The research team plans to confirm these findings in human samples. While it is clear that females also develop health problems with obesity, the fact that there was such a difference in the vascularization in male and female fat may mean it would be more effective to have different treatments for males and females.

https://www.sciencedaily.com/releases/2018/10/181023130529.htm