Fluid intelligence—the type of intelligence that involves short-term memory and the ability to think quickly, logically, and abstractly in order to problem-solve in new and unique situations—peaks in young adulthood (between the ages of 20 and 30), levels out for a period of time, and then generally starts to slowly decline as we age. But while aging is inevitable, scientists are finding out that certain changes in brain function may not be.
One study from Iowa State University, published in the November 2019 edition of Brain, Behavior, and Immunity, found that muscle loss and the accumulation of body fat around the abdomen, which often begin in middle age and continue into advanced age, are associated with a decline in fluid intelligence. This suggests the possibility that lifestyle factors, such as the type of diet you follow and the type and amount of exercise you get throughout the years to maintain more lean muscle, might help prevent or delay this type of decline.
The researchers looked at data that included measurements of lean muscle, abdominal fat and subcutaneous fat (the type of fat you can see and grab hold of) from more than 4,000 middle-to-older-aged men and women and compared that data to reported changes in fluid intelligence over a six-year period. They found that middle-aged people with higher measures of abdominal fat scored worse on measures of fluid intelligence as the years went by.
For women, the association may be attributable to changes in immunity that resulted from excess abdominal fat; in men, the immune system did not appear to be involved. Future studies could explain these differences and perhaps lead to different treatments for men and women.
Meanwhile, there are steps you can take to help reduce abdominal fat and maintain lean muscle mass as you age in order to protect both your physical and mental well being. The two most generally recommended lifestyle approaches are maintaining or increasing your levels of aerobic exercise (which, for some people, could be achieved by simply walking more throughout each day) and following a Mediterranean-style diet that is high in fiber from whole grains, vegetables, and other plant foods and eliminates highly processed foods. If you carry extra belly fat, speak with your health care provider to determine a plan that is best for you.
Klinedinst BS, Pappas C, Le S, et al. Aging-related changes in fluid intelligence, muscle and adipose mass, and sex-specific immunologic mediation: A longitudinal UK Biobank study. Brain, Behavior, and Immunity. November 2019; 82:396-405.
When does cognitive functioning peak? The asynchronous rise and fall of different cognitive abilities across the lifespan. Psychological Science. April 2015; 26(4): 433-443.
Magriplis E, Andrea E, Zampelas A. Nutrition in the Prevention and Treatment of Abdominal Obesity (Second Edition, 2019) The Mediterranean Diet: What it is and its effect on abdominal obesity. Pages 281-299.
Cowan TE, Brennan AM, Stotz PJ, et al. Separate effects of exercise amount and intensity on adipose tissue and skeletal muscle mass in adults with abdominal obesity. Obesity. September 27, 2018