A new research from Iowa State University reported that as a person grows older, decreased muscle mass along with increased body fat percentage could seriously affect the immune system and hinder fluid intelligence, or the ability to reason and think flexibly. Published in the journal Brain, Behaviour, and Immunity, the research was led by Auriel Willette, assistant professor of food science and human nutrition, and Brandon Klinedinst, a PhD student in neuroscience. They looked into data collected from over 4000 men and women, middle-aged to older.
The team looked at lean muscle mass, abdominal fat and subcutaneous fat, and how they were related to changes in fluid intelligence—across a span of six years. People with higher amounts of belly fat in their 40s and 50s had lesser capacity for flexible thinking than others. On the contrary, higher muscle mass seemed to help.
The research looked at whether links between fat or muscle and fluid intelligence was related to the immune system. Other studies conducted earlier have demonstrated that overweight or obese people, those with a higher body mass index (BMI) than desirable, have more immune system activity in their blood, which can activate the immune system in the brain and cause issues with learning. But it is to be noted that BMI only takes into account total body mass, not the connection between fat and muscle, so it has not been clear whether fat, muscle, or both kickstart the immune system.
According to the Iowa State University report, in women, the connection between more abdominal fat and lesser intelligence was explained by alterations in lymphocytes and eosinophils, two types of white blood cells. In men, a different white blood cell, basophils, was the root cause. They came to the conclusion that while muscle mass acted as a protection, the immune system had little effect.
These findings can lead to new treatments that help maintain mental flexibility in ageing adults with obesity or sedentary lifestyles. Exercise routines, especially strength training, becomes essential as a person grows older. Women, who naturally have less muscle mass than men, should be even more alert to changes in their body shape to maintain a healthy brain. In conclusion, says Willet, ‘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.’