STORY AT-A-GLANCE
- Increasing research shows that maintaining healthy levels of body fat and greater muscle mass has an effect on your brain health and may slow your rate of cognitive aging
- People with higher amounts of abdominal fat had worse fluid intelligence with age, while those with greater muscle mass were more protected against such declines
- Women who had greater muscle mass tended to have better scores in fluid intelligence during the study period
- Past research has linked midlife obesity with an increased risk of mild cognitive impairment, changes in short-term memory and executive functioning and dementia
What’s more, the amount of muscle and fat you have may be a more important factor in how your level of fluid intelligence decreases over time than your chronological age. Your chronological age, i.e., your age in years, is just a numerical measurement, but your real age is your biological age as dictated by your choices and habits, as well as your modifiable risk factors like levels of muscle and fat.
More Muscle, Less Fat Protects Your Brain
In a study by Iowa State researchers, data from 4,431 adults were examined to compare levels of lean muscle mass, abdominal fat and subcutaneous fat with changes in fluid intelligence — the ability to solve problems in new situations — over a six-year period.[2][3]Those with higher amounts of abdominal fat had worse fluid intelligence with age, while those with greater muscle mass were more protected against such declines. In fact, women who had greater muscle mass tended to have better scores in fluid intelligence during the study period.
Study co-author Auriel Willette, assistant professor of food science and human nutrition at Iowa State University, said in a news release, “Chronological age doesn’t seem to be a factor in fluid intelligence decreasing over time. It appears to be biological age, which here is the amount of fat and muscle.”[4]
What’s more, the study revealed a link between the immune system and how changes in fat levels affect cognition. Previous research suggests a higher body mass index (BMI) leads to greater immune system activity in the blood, which in turn activates the immune system in the brain, with a negative outcome on cognitive function.[5]
The featured study also found that changes in white blood cells called lymphocytes and eosinophils explained the link between abdominal fat and worsening fluid intelligence in women. In men, basophils, another type of white blood cell, were linked to about half of the link between fat levels and fluid intelligence, the study found.[6]
How Obesity Affects Your Brain
Obesity has multiple effects on the brain, including anatomically speaking. Obese individuals may have reduced gray matter in brain regions such as the hippocampus, prefrontal cortex and other subcortical regions. Atrophy in the hippocampus, in turn, has been linked to Alzheimer’s disease.[9]Gray matter is the outer layer of the brain associated with high-level brain functions such as problem-solving, language, memory, personality, planning and judgment. Even in elderly people who are otherwise cognitively normal, obesity is associated with measureable deficits in brain volume in the frontal lobes, anterior cingulate gyrus, hippocampus, and thalamus compared to individuals with a normal weight.[10]
Further research published in Radiology found that obesity may lead to alterations in brain structure, shrinking certain regions.[11] Among men, higher total body fat percentage was linked to lower brain gray matter volume. Specifically, 5.5% greater total body fat percentage was associated with 3,162 mm3 lower gray matter volume.
Among men, 5.5% greater total body fat was also associated with 27 mm3 smaller globus pallidus volume, an association also seen in women. In women, 6.6% greater total body fat percentage was associated with 11.2 mm3 smaller globus pallidus volume.
The globus pallidus is a brain region that plays a role in supporting a range of functions, including motivation, cognition and action.[12] Obesity was also associated with changes in white matter microstructure, which may be related to cognitive function.[13]
Obesity-Associated Health Problems Also Harm Your Brain
Obesity’s effects on brain health are also due to its associated health problems, including heart disease, diabetes and atherosclerosis, each of which can have its own deleterious effects on your brain. For instance, as noted in Frontiers in Neuroscience:[15]“Obesity-derived vascular problems, such as atherosclerosis and arteriosclerosis, which are systemic diseases, are known to affect the steady blood flow of vessels that feed the brain, thus contributing to cognitive impairment or even stroke, where large areas of the brain die due to the stop in the blood flow of a major brain artery caused by a blood clot.”In terms of diabetes, of which obesity is a key risk factor, having this condition in midlife is associated with a 19% greater cognitive decline over 20 years compared with not having the condition.[16] Even those with prediabetes had significantly greater cognitive decline than those without.
Indeed, “Epidemiological studies have linked type-2 diabetes mellitus with cognitive impairment and dementia, with insulin resistance and hyperglycemia as the probable mechanistic links,” researchers noted.[17]
The Inflammation Connection
Obesity can trigger chronic inflammation in your body, and chronic inflammation in your brain (neuroinflammation) is known to impair neurogenesis, your brain’s ability to adapt and grow new brain cells. It’s also linked to neurodegenerative disorders such as Alzheimer’s disease (AD), and it’s been suggested that “Obesity may serve as an amplifier or initiator of the chronic inflammation observed in AD patients.”[20]Further, higher levels of inflammatory markers have also been associated with lower brain volume, including “greater atrophy than expected for age.”[21] Excess body fat, particularly visceral fat, is also related to the release of proteins and hormones that can cause inflammation, which in turn can damage arteries and enter your liver, affecting how your body breaks down sugars and fats.
Strength Training Is Good for Your Brain
While obesity takes a toll on your brain, increased muscle mass protects it, which is likely one reason why strength training has been found to be beneficial for your brain. In other words, your body’s physical strength may serve as a marker of your brain power.“Taken together, during aging processes, a substantial decline in muscular strength, especially in lower limb muscles, occurs, and accumulating evidence suggests that lower muscular strengths are linked to poorer cognitive performance.
