Americans are bulking up around the waist, and that spells trouble for the brain. The average waist size in this country has increased from 37.6 inches in 1999 to 38.8 inches in 2012, according to the latest Centers for Disease Control and Prevention (CDC) figures. The agency estimates that 70 percent of Americans are overweight, and of these, 39.5 percent of adults ages 40 to 59 and 35.4 percent of adults 60 or older are obese.
We know excess weight takes a toll on physical health, upping risk for heart disease, stroke, cancer, type 2 diabetes, and more. But there is also plenty of evidence that being overweight or obese can harm cognition, especially as a person ages, and that it negatively impacts brain health in a number of ways.
“It is thought that the negative effects of obesity on cognitive function are related to inflammation, but it probably involves many other factors as well, ” says Louisa Sylvia, PhD, Associate Director of Psychology in the Bipolar Clinic and Research Program at Massachusetts General Hospital (MGH). “We are just starting to understand the complex relationship between obesity and cognition.”
The good news is that there is evidence that losing weight might help reverse some weight-related harm to the brain. In a study published in the August 2014 issue of the Journal of Clinical Endocrinology & Metabolism, researchers assessed a small group of obese individuals before and after they underwent bariatric surgery. The scientists looked at brain scans and measures of cognitive function and found that six months after their gastric bypass surgery, participants no longer showed signs of abnormal overactivity in certain brain regions, and had improved significantly in measures of executive function (organizing, planning, and decision-making). The study follows previous work that documented improvements in attention and memory after bariatric surgery, as well.
“This is a small, but very interesting study that speaks to the fact that weight loss is associated with better cognitive functioning in people who are overweight,” says Dr. Sylvia. “However, other recent research suggests that excess weight may be only one of a combination of factors linked to cognitive decline in obese individuals, including lack of physical activity, poor diet, and depression. Addressing this complicated interplay of factors in addition to losing weight may be the best way to preserve brainpower.”
Fat harms the brain
Scientists have linked excess weight to a number of brain ills, including long-term declines in cognition, greater risk for Alzheimer’s disease (AD) and dementia, increased brain atrophy, decreased processing speed, decreased attention, and deficits in executive functioning. What’s more, these effects seem to grow more pronounced with age, researchers have found.
One study in animals suggests that excess fat accumulation may directly affect the brain in ways that injure brain calls and cause deterioration in brain functioning. Obesity and overconsumption of foods high in saturated fats and simple carbohydrates have been found to weaken the blood brain barrier (BBB), a semipermeable membrane that helps protect the central nervous system and brain from pathogens and toxins circulating in the bloodstream. Recent research suggests that in obese mice, a pro-inflammatory substance created by fat cells called interleukin 1 is able to pass through the weakened BBB and enter the brain’s hippocampus, a key area involved in memory and learning.
According to the research, which was published in the February 2014 issue of The Journal of Neuroscience, interleukin 1 promoted inflammation that appeared to cause damage to brain tissue and to impede the normal functioning of synapses, or connection points between brain cells. Compared to a group of healthy mice, the obese mice performed poorly on tests of memory and thinking, but when their fat cells were surgically removed or they were forced to exercise and lose fat, their brain interleukin 1 levels dropped to normal and the animals’ cognition dramatically improved. In contrast, previously slender mice that received implants of fat experienced a rise in interleukin 1 levels and associated cognitive decline.
Researchers are looking into other ways that obesity might promote cognitive decline, including by causing negative changes in the brain’s white matter and deterioration of cerebral blood vessels related to factors such as atherosclerosis, diabetes, or high blood pressure. Some research suggests that a poor diet high in saturated fats, sugar, and simple carbohydrates, consumed by many obese and overweight individuals, may produce pathological changes in brain circuits and structures, disrupting normal cognition and increasing susceptibility to overeating and weight gain.
Healthy lifestyle choices
“If you are overweight or obese, losing weight can be helpful, both to protect your brain and to improve your overall physical wellbeing,” says Dr. Sylvia.
“I usually encourage people starting a diet to focus on making healthy lifestyle choices rather than just losing weight, as weight loss is only one way to promote improved health.”
Among her lifestyle suggestions are:
Get the nutrients you need. Bone up on the basic rules of good nutrition and apply them. Don’t stock your pantry with junk foods.
Don’t eat unless you’re hungry. There is no evidence that missing a meal has a negative impact on health.
Eat in moderation. Instead of stuffing yourself, stop eating when you’re satisfied. Resist cravings by recognizing that food urges are not based on hunger and last only a short time. Try to distract yourself until they pass.
Skip the alcoholic drinks. They provide extra calories and little else.
Exercise. Regular physical workouts increase overall fitness, burn excess calories, and benefit your brain.
Reduce stress. Relaxation techniques such as meditation, listening to music, or taking a relaxing bath are examples of ways you can reduce stress levels that might tempt you to soothe yourself with food.
Turn off the TV. Replacing sedentary “tube” time with more active pursuits, such as hobbies, gardening, or taking a walk after dinner, can help you lose weight and lead to new interests.
Keep a regular sleep schedule with the same target time for going to bed and getting out of bed.
To eat better, Dr. Sylvia suggests adhering to the concept of “Eating Naked” (see What You Can Do), which focuses on natural, unprocessed foods. Base your meal plans on Harvard’s Healthy Eating Plate—with one-half of your plate devoted to vegetables and fruits, one-quarter of your plate devoted to whole grains rather than refined grains, and the remaining quarter devoted to unprocessed proteins, such as fish, chicken, beans, and nuts. Choose healthy plant oils, such as canola and olive oil, and drink water, coffee, or tea.