SAN FRANCISCO — Exercise by itself is unlikely to lead to weight loss, but becoming physically fit reduces a person's risk for mortality or cardiovascular death regardless of weight, Dr. Robert Baron said at a meeting on diabetes and endocrinology sponsored by the University of California, San Francisco.
A 2006 meta-analysis of 43 randomized, controlled studies of exercise to treat obesity in 3,476 patients found small weight losses from exercise alone compared with no intervention. The difference between groups often did not achieve statistical significance (Cochrane Database of Syst. Rev. 2006;DOI:10.1002/14651858.CD003817.pub3). Many of the studies used smaller exercise doses than now would be considered the standard of care, said Dr. Baron, professor of medicine at the university.
The investigators then focused a more formal meta-analysis on a subset of relatively homogenous studies that typically compared exercise plus a weight-loss diet to treatment using the diet alone. They found a statistically significant, modestly better weight loss in the combination group, in which patients lost 1.1 kg more than did the diet group.
Studies that employed a higher frequency, duration, or intensity of exercise, however, produced a 1.5-kg greater weight loss in the exercise-plus-diet group. In those studies, patients in the exercise groups improved their blood pressures, fasting blood glucose measurements, and triglyceride levels regardless of whether they lost weight.
Discussions about “fit versus fat” in recent years largely originated with the 1999 Aerobics Center Longitudinal Study (ACLS), which reported mortality benefits from fitness even in overweight or obese men. In the 14-year observational study of 25,714 men, the relative risk of death in men who were fit was only 10% higher in overweight or obese men compared with normal-weight men. In men who were not fit, however, the risk of death doubled in normal-weight men, was 2.5 times higher in overweight men, and tripled in obese men compared with fit, normal-weight men (JAMA 1999;282:1547–53).
More recent studies have attempted to confirm these findings. An analysis of data on 116,564 women in the Nurses Health Study found less impressive—but still beneficial—effects of fitness in a 24-year observational study. Compared with normal-weight, active women, the relative risk of death was 1.6 in normal-weight, inactive women, 1.9 in overweight, active women, and 2.6 in overweight, inactive women (N. Engl. J. Med. 2004;351:2694–703).
A separate analysis of data on 19,173 men from the ACLS found that fitness decreased the risk of death from cardiovascular disease in patients with metabolic syndrome in any weight group (Diabetes Care 2005;28:391–7). In the normal-weight group, metabolic syndrome doubled the risk of cardiovascular mortality, but the risk was only 1.6-fold higher in fit men with metabolic syndrome compared with fit, healthy controls.
In the overweight group, fitness normalized a slightly higher risk among healthy men as a whole compared with normal-weight men. A 1.8-fold higher risk in men with metabolic syndrome became a 1.2-fold higher risk with fitness. Among obese men with or without metabolic syndrome, a nearly threefold higher risk for cardiovascular death was halved among fit men.