It’s a fact that obesity dulls the brain. A slew of research shows that when weight piles on around the middle, inflammation increases in the brain, shrinking key processing areas, and leading to reduced concentration and memory loss. Middle-age spread, the excuse that comes with advanced years, means those who add pounds with age are at an increased risk of dementia and Alzheimer’s — and if that doesn’t get you to the gym, nothing will.
A recent study in The Journal of Neuroscience detailed the “milkshake test”: Scientists scanned the brains of women who drank a milkshake, and saw the striatum — a subcortical part of the forebrain responsible for movement, motivation and reward — light up. Six months later, they repeated the test: The brains of women who had gained weight in the interim failed to respond to the milkshake this time, their brains had become dulled by fat. So, a little like an addict who needs more heroin or cocaine over time to get a high, people who consume a lot of sugar or carbs start consuming more in order to get that same dopamine high.
Of course, the middle-aged and the elderly are hardly the only two groups at risk. The impact of obesity on children has been a particular concern. In a recent study, reported by the American Academy of Child and Adolescent Psychiatry, the adjacent orbitofrontal cortex, which controls decision-making and impulsivity, was observed to be smaller in children who are overweight. With this part of the brain reduced, so too is the ability to turn away from a plate of cookies.
Dr. Antonio Convit, of the New York University School of Medicine, says, “There is a vicious cycle, where obesity leads to inflammation, which damages certain parts of the brain, which in turn leads to more disinhibited eating and more obesity.”
This is echoed by research from the Institute of Metabolic Science at the University of Cambridge, in the United Kingdom, where researchers found genetic mutations in the hypothalamus of obese children, the area of the brain concerned with metabolism, body temperature, thirst, fatigue, sleep, and attachment in relationships. However, it may not always leave a permanent effect.
The good news is that one of these mutations is dramatically curable if the patient receives a daily injection of a recombinant protein called leptin, which can then reverse it. Cambridge’s Department of Pharmacology is now studying hypothalamic anatomy and function to further explore the circuitry in our brains that may lead us to eat beyond what our metabolisms can process at a time.
Another obesity disorder, known as melanocortin-4 receptor deficiency, is present in 5 to 6 percent of severely obese children and 0.5 to 1 percent of obese adults. Remarkably, the mutant receptor can predict spontaneous food intake behavior at a test meal in individuals who have this genetic defect. Further research at Cambridge has also implicated the brain’s neurotrophin system in the regulation of human appetite and body weight.
The importance of this research is considerable. Belly fat is associated with a decrease in total brain volume in middle-aged adults, especially menopausal women, according to a study published in the Annals of Neurology, and another one with similar findings in the Journal of the American Geriatric Society. This visceral fat releases hormones that increase inflammation, damaging the immune system and certain areas of the brain.
The American Geriatric Society looked at memory test scores for 8,745 women aged 65 to 79, and found that a one-point increase in a woman’s body mass index correlated to a one-point decrease on memory tests.
Further, research at the University of California, Los Angeles, found that obese, elderly individuals had 8 percent lower brain mass than those of appropriate weight. People who were simply overweight had 4 percent less brain volume than their slimmer counterparts.