Everyone knows what fat is. It’s where the extra calories you eat end up and the reason your clothes fit too tightly. But beyond that, it doesn’t do much, right?


While fat, or adipose tissue, is a place to store excess energy, research shows that it also plays an active role in health and disease. In fact, your fat may be keeping you fat!


The good news is that weight loss and regular exercise can reverse the negative health effects of excess body fat.


Body fat is essential for storing extra energy, something that allowed our caveman ancestors to survive times when food was scarce. But fat cells have important biological functions beyond storing extra energy.


It turns out that fat cells release chemical signals called adipokines that have effects on other organs and tissues.


For example, type 2 diabetes is strongly linked with obesity. Type 2 diabetes is a condition of high blood glucose caused, in large part, by cells not responding to the hormone insulin.


Resistin, which is produced by fat cells, has the effect of promoting insulin resistance in the liver and muscle, the two major places where excess glucose is stored.


The result is high blood glucose, the hallmark characteristic of diabetes.


Fat cells also secrete adipokines such as leptin and TNF-alpha that promote inflammation and abnormal function of blood vessels. This is associated with atherosclerosis, the development of cholesterol-containing plaques that form in blood vessels.


These plaques may be unstable and rupture, leading to clot formation that causes a heart attack.


This is one reason why obesity is a major risk factor for cardiovascular disease.


The hormone leptin also plays an important role in regulating body fat stores. Leptin signals the brain about the amount of fat stored in the body.


When body fat stores decrease, leptin stimulates appetite to increase energy intake and storage as fat; when body fat increases, appetite is reduced.


At least that is the way it is supposed to work. The effect of leptin on appetite is only a suggestion, and it is easy to eat despite it. The result is excess energy intake which leads to obesity.


Worse, the brain develops a resistance to the high levels of leptin produced by the excess body fat and establishes a new “normal” level.


When someone loses weight and leptin levels go down, the brain responds by increasing appetite. Is it any wonder why losing weight and keeping it off is so difficult?


The good news is that losing weight and body fat, no matter how difficult it can be, can reduce the negative effects of these adipokines.


The even better news is that exercise can reverse some of this damage, even if you don’t lose weight.


The reason is that, like adipose tissue, muscle produces chemical signals, too.


These myokines also have beneficial effects include improving insulin sensitivity and reducing inflammation.


This is one way in which regular muscle activity (exercise) is thought to promote good health.


Myokines can also counteract the negative effects of adipokines by creating a balance between the two opposing effects.


In fact, the myokines that are stimulated by exercise can have a greater effect than the adipokines. This helps explain why being obese but physically fit may actually be healthier than being a normal weight but unfit.


The bottom line is that excess fat is unhealthy, and we are starting to understand the mechanisms that explain why.


Losing weight is important for improving your health. And exercise may be even more important, so you should strive to be more active regardless of your body weight.


Brian Parr, Ph.D., is an associate professor in the Department of Exercise and Sports Science at USC Aiken where he teaches courses in exercise physiology, nutrition and health behavior.