A new study shows that a combination of diet and physical activity can reduce LDL cholesterol levels in men and postmenopausal women at risk for coronary heart disease because of elevated levels of LDL ("bad" cholesterol) and reduced HDL ("good cholesterol"). The diet was based on the American Heart Association "Step 2" guidelines which are recommended for individuals with high LDL cholesterol and involve reducing intake of saturated fat to less than 7 percent of calories, and reducing cholesterol intake to less than 200 mg per day.
Exercise consisted of engaging in aerobic activity equivalent to walking or jogging 10 miles per week. Diet and exercise were continued for one year. The study reports that statistically significant reductions of LDL cholesterol were not observed in individuals who followed a regimen of either diet alone or exercise alone.
The American Heart Association agrees with the researchers that this study provides further support for combining physical activity and diet in reducing risk for heart disease and stroke.
"However, we cannot conclude from this study that diet by itself is ineffective in lowering LDL levels," says Ronald M. Krauss. M.D., a member of the American Heart Association's Nutrition Committee. Krauss is also a senior scientist at the Lawrence Berkeley National Laboratory at the University of California at Berkeley.
"Average reductions in LDL cholesterol levels with the Step 2 diet were 5 to 7 percent which is very consistent with the changes that would be predicted on the basis of many previous studies," says Krauss. However, the statistical analysis of the study's results concluded that these changes were not significant.
Individuals have wide differences in their cholesterol response to diet, with many individuals showing much larger than average reductions in LDL, and others showing no change or increases. The responses vary greatly because there are many metabolic and genetic factors influencing LDL cholesterol levels in individuals. A study such as this, with relatively small dietary changes and small groups, may not be large enough to provide an adequate test of the diet alone or exercise alone.
"Individuals should not be discouraged from trying to reduce levels of LDL cholesterol with diet, since many people can achieve a beneficial response. This study suggests the diet may be more effective when combined with increased physical activity," he says.
The study also failed to confirm earlier evidence that exercise increases levels of the protective HDL cholesterol. However, the diet and exercise regimens that were used resulted in relatively small weight changes -- the average reductions were less than 5 percent. Previous studies have suggested that a greater weight loss, and over a sustained period, may be necessary to achieve an increase in HDL and other beneficial metabolic changes.
Journal
New England Journal of Medicine