The Bill & Melinda Gates Foundation recently funded an analysis of obesity in the U.S. The analysis highlighted the fact that obesity rates vary in different states. The results are disturbing. About 75 percent of all Americans are currently overweight or obese. In 2021, over 15 million children and young adolescents and 172 million adults were overweight or obese. Texas, West Virginia, Mississippi, Kentucky, North and South Dakota, Iowa, Indiana, Arkansas, Alabama, Nebraska, and most of the states in the southeastern U.S. had the highest prevalence of overweight and obese citizens.
Obesity’s Effects on Brain Function
Among the reasons that this is concerning is that obesity has consequences for brain function.
A higher BMI is consistently associated with poor performance on working memory tasks. Eating a poor diet every day may not immediately impair thinking, but eating a poor diet for many years, resulting in obesity, will impair daily cognitive abilities. Obesity shrinks critical brain regions and increases the risk of cognitive decline. Increased adiposity has a demonstrated direct negative effect on brain health via mechanisms triggered by central inflammation and insulin resistance, with the most pronounced decrements observed for cognitive domains that are prefrontal- and hippocampal-dependent. Many laboratories around the world, including my own, have documented the mechanisms that underline how excessive obesity will significantly impair overall cognitive function.
How does obesity contribute to brain shrinkage and cognitive decline? A few years ago, it became clear that fat cells produce inflammation by releasing specialized proteins called cytokines. The more fat cells you have, the more cytokines get released into your blood.
I study the effects of cytokines in the brain. A few years ago, I published a series of studies demonstrating how these inflammatory proteins are capable of shrinking brain regions that are used in the process of learning new things and recalling memories. The linkage between excess body fat and cognitive function is confirmed by studies that have shown that weight loss is associated with improvements in cognitive function.
An Epidemic With National Consequences
What are the national consequences of obesity on brain function?
Measuring body weight is a much easier task than estimating its effect on brain function. Each year, U.S. News & World Report publishes the status of educational resources and achievements in each state. The U.S. Department of Education’s National Center for Education Statistics reported that over 50 percent of Americans between the ages of 16 and 74 read below the equivalent of a sixth-grade level. In 2024, the states with the lowest number of high school and college graduates—West Virginia, Mississippi, Arkansas, Louisiana, Kentucky, Oklahoma, Alabama, and Indiana—also reported the highest percentage of obese citizens. Research suggests a correlation between poverty and obesity, particularly in states with the highest poverty level (Mississippi, West Virginia, Arkansas, Louisiana, Kentucky, Alabama, Oklahoma, and Tennessee, according to the Census Bureau, Annual Survey of School Systems Finances).
The Importance of Food Choices
The brain has evolved to reward us for eating less nutritious foods, particularly fat, salt, and sugar (or other simple carbohydrates). These three nutrients were very rarely part of the human diet for most of our evolutionary history. The brain evolved multiple overlapping neural systems (dopamine, endocannabinoid, and endogenous opioid) to reward us for consuming fat, salt, and sugar to completion whenever they appeared. For example, numerous ancient human settlements were centered around natural salt deposits. Today, the highest-calorie foods that are driving the obesity epidemic, such as fast foods, processed meats, desserts, candies, fatty meats, white bread products, snacks, sugary drinks, alcohol, and condiments, are also the cheapest. Not surprisingly, poorer people are less able to afford nutritious foods.
This risk factor is preventable. It’s just not easy. The brain did not evolve to reduce its food intake. A trainer for the popular NBC television show The Biggest Loser used to claim that more exercise was all that was necessary to lose weight. After many years of helping severely obese people lose weight, however, Bob Harper concluded that exercise is not the key; your diet matters the most. Not only is Harper helping his clients to feel better and achieve their personal goals, but he is also helping them to live longer, healthier lives. Most of his clients became obese because they ate too many calories. Visit any gym or spa and you will see that people exercising carry a significant amount of body fat overlying their muscles even as muscles get bigger and stronger. Excess body fat accelerates aging and increases our risk of dying because fat cells produce inflammation.
Diet vs. Exercise
Researchers recently investigated whether diet or exercise most effectively reduced the levels of inflammation in overweight or obese women. After 12 months, the scientists concluded that the greatest weight loss and most significant reduction in the level of inflammatory protein reduction came only from dieting, not exercising. The evidence overwhelmingly indicates that caloric restriction is the only valid, scientifically proven dietary intervention that can reduce body weight, slow the aging process, and improve Mental health.
