Scientists are beginning to uncover evidence that exercise can play a major role in managing diabetes, even in obese or overweight patients who lose little weight, reported experts at the 72nd Scientific Sessions of the American Diabetes Association.
Clinicians have long been aware of the clear relationship between diabetes and obesity, and they often suggest exercise as a component of obesity treatment—with the caveat that exercise itself is helpful, but not sufficient, for treating obesity. But what if moderate amounts of exercise were enough to treat obesity-induced diabetes?
There’s long-standing evidence that physical fitness can help people live longer, even those who carry too many pounds. Seminal research by Steven Blair, PED (then at the Cooper Institute of Aerobics Research in Dallas, Texas) and colleagues found that cardiovascular fitness is strongly associated with improved survival and is independent of body weight (Blair SN et al. JAMA. 1989;262:2395-2401). Further studies have extended these findings, showing that physical fitness is closely associated with diabetes, also independent of body fatness.
There is a dramatic, steep increase in mortality among patients with very low fitness scores. “Actually, it is not fitness we are concerned about but rather low fitness,” said Carl Lavie, MD, of the John Ochsner Heart and Vascular Institute in New Orleans, who spoke at a symposium on the importance of fitness on the pathophysiology and treatment of diabetes. Although both fitness and fatness are important, cardiorespiratory fitness greatly modifies the association of obesity with death due to cardiovascular disease, he said.
The underlying mechanism, explained John Thyfault, PhD, an exercise physiologist at the University of Missouri, appears to be the key role that muscle plays in how the body processes glucose. The best indicator for the risk of developing diabetes or cardiovascular disease is the glucose response when food is consumed. The release of insulin following food ingestion facilitates glucose transport into muscle and fat and inhibits a mechanism the body uses to keep blood glucose levels from dropping too low, hepatic gluconeogenesis (the generation of glucose in the liver from substances other than carbohydrates, such as lactate). About 80% of circulating glucose is transported into muscle, making it the most important organ in maintaining proper glucose levels.
Most research into causes of diabetes has focused on mediators of insulin resistance in the muscle, with much less attention paid to the effects of how inactivity and a lack of muscle contractions mediate and are necessary components for the development of insulin resistance and a disruption of overall glucose homeostasis. As it turns out, even very modest changes in physical activity or exercise substantially improve insulin sensitivity, glucose transport into muscle, and glucose homeostasis. For example, studies in animal models of diabetes show that the disease can be prevented in animals that are allowed to exercise. In the 1980s, studies demonstrated that athletes and other “physically trained” individuals who lowered their physical activity experienced increased insulin resistance. More recently, Thyfault and colleagues showed that sedentary people can markedly improve their glucose dynamics with very modest amounts of exercise.
Taken together, these findings point to exercise as having an important role in the treatment of patients with diabetes. Even though little weight loss may result from physical activity, substantial improvements in diabetes management can occur, as can improved longevity. And emerging evidence indicates that the greatest risk to health is sedentary behavior and that any exercise or increase in physical activity is better than none.
There’s a useful message that can be taken from this area of research, said Lavie. Patients with diabetes as well as obese patients should be encouraged to exercise. Individuals with diabetes also may benefit from resistance training and increases in muscular strength, Lavie added. And because such benefits mostly are the result of not being sedentary as opposed to being superbly fit, lifesaving exercise should be an achievable goal for most individuals, even when they cannot lose weight.