How Body Fat Hurts your Brain

By: 
Elise Brett, MD, FACE, ECNU

It’s a fact: Being overweight is bad for your brain.

How Body Fat Hurts your Brain

Compared with normal weight individuals, people who are overweight in midlife have a 30 percent greater risk of developing dementia (memory loss and decreased cognitive function) such as Alzheimer’s disease later in life. Not only that, but obesity is associated with smaller brain sizes and decreased cognitive function in middle-aged people.

Besides high body mass index (BMI, a measure of body fat based on an individual’s height and weight), central obesity (large waist circumference) is also associated with dementia and so is type 2 diabetes, which is more common in people who are overweight or obese. People with type 2 diabetes have twice the risk for dementia and, as a group, perform worse than people without diabetes on tests of cognitive function on memory.

While it is possible that certain factors other than fat mass are at play, such as high-fat, high-calorie diets, lack of intake of certain vitamins or other nutrients and higher alcohol use, there is mounting evidence that fat itself affects the brain. Scientists used to believe that fat mass was an inactive reserve of body tissue. We now know that fat is an active endocrine organ that secretes numerous substances that have an effect on the rest of the body. These substances are called “adipocytokines,” [ad'i-pō-sīt-o-kīns] and are involved in metabolism and inflammation.

Many such substances may play a role in the development of dementia, but the two with the most convincing scientific evidence are “adiponectin” [ad'i-pō-nek'tin] and “leptin.” Adiponectin is involved in the regulation of energy expenditure, sugar metabolism and fat metabolism and is higher in thin individuals. Adiponectin blocks production of inflammatory “cytokines” [si-to-kins] and has been shown to have effects on protecting the brain. Rats who do not make adiponectin have been shown to be more susceptible to strokes.

Leptin is involved in the long-term control of body weight. New evidence shows that leptin also probably plays a role in memory, nerve growth, nerve protection and brain structure. Leptin improves nerve survival and slows nerve damage in animals with dementia. Giving leptin directly to mice brains improves their memory. People with obesity have high leptin levels, but also have leptin “resistance,” so the normally protective actions of leptin are not as effective. It has also been shown that in obese people, leptin may not reach the brain in adequate levels.

Thus, there is increasing evidence for a direct causal role of fat mass in the development of dementia. As our country’s population lives longer and simultaneously becomes fatter, obesity-related dementia may present a substantial public health problem. Treatments for dementia are only minimally effective, yet another reason to try to achieve and maintain healthy weight in midlife.

Dr. Elise M. Brettis Associate Clinical Professor at the Icahn School of Medicine at Mount Sinai and is in private practice specializing in Endocrinology and Metabolic Support in New York City. Dr. Brett completed her undergraduate education at the University of Michigan, received her medical degree from Mount Sinai School of Medicine, and completed her internal medicine residency and fellowship in endocrinology and metabolism at The Mount Sinai Hospital. She is board certified in endocrinology and metabolism