Obviously, overeating unhealthy foods can lead to overweight. But looking beyond direct effects on expanding waistlines, our lab studies how mental functioning is related to diet. We’ve found a troubling link between a fat-rich diet common in the West and brain-related ailments that can actually impair our ability to avoid overeating.
Many scientists believe that societal factors, such as advertising, have combined to create an environment in which the temptations to eat have overwhelmed our body’s natural biological ability to control what and how much we consume. The result is that in the United States, two-thirds of adults, and more than one third of children and adolescents, are now overweight or obese. This trend is spreading to other countries all over the world. Even worse, diseases that are associated with excess body weight – such as diabetes, high blood pressure and heart problems – are also becoming more prevalent.
At the core of the problem is the fact that many of the foods we can’t seem to resist are unhealthy. Some of the most attractive and popular foods in our current environment contain high amounts of saturated fats – high levels are found in red meats and dairy products like ice cream and butter. This type of diet is consumed by so many people in the US and other western societies that it is often called the “western diet.” No wonder obesity has become such a problem.
Over the past several years, many scientists have reported that consuming a western diet and gaining excess body weight may have harmful effects on the brains of both human and nonhuman animals. For example, some research suggests that middle-aged adults who are overweight and obese are at greater risk for developing Alzheimer’s disease and other types of late-life cognitive dementias compared to people of normal weight. The results of other studies suggest that even children as young as seven years of age may suffer certain types of memory impairments as a consequence of consuming too much of a western diet and accumulating too much body fat.
Much information about the nature of the effects of western diets on the brain comes from studies with rats and mice. Research in our lab and elsewhere has repeatedly shown that feeding rats a diet with levels of saturated fat and sugar much like those in the human western diet weakens the blood-brain barrier (BBB). The BBB is a system of cells and membranes that form tight junctions to prevent harmful agents that circulate in the bloodstream from entering the brain. Feeding rats a western-style diet weakens those tight junctions and thereby allows potentially harmful substances to pass into the brain.