Lifestyle modifications such as diet, exercise and weight control have long been recommended as a possible way to prevent high cholesterol and atherosclerosis, or coronary artery disease. The new results show for the first time that exercise without the appropriate dietary intervention did not prove beneficial and, in some cases, may actually have done harm.
Using an animal model, the researchers fed one group of mice a high-fat diet along with putting them on an exercise program, while the other group of mice exercised but ate a high protein/fish oil regimen, more along the lines of a traditional Mediterranean diet. They then compared the mice to a group that did not exercise at all.
“What we found was that there was no benefit to exercise in those who ate a bad diet — their cholesterol still increased and so did their coronary artery disease,” said Keith Webster, Ph.D., director of the Miller School’s Vascular Biology Institute, professor of molecular and cellular pharmacology and senior author of the study, titled An essential role for diet in exercise-mediated protection against dyslipidemia, inflammation and atherosclerosis in ApoE-/-Mice.
“This study is further evidence that you cannot continue to eat a bad diet and think you will burn it all off through exercise. When you exercise you take in more calories in general, and if those calories are from high-fat foods, you are putting yourself more at risk than if you did not exercise at all.
“While our studies were done on mice, much of the evidence from epidemiology as well as clinical trials on the impact of diet and/or exercise on blood lipids and atherosclerosis supports an extrapolation of the fundamental observations of our study to humans.”
The researchers acknowledge that both exercise groups lost more weight than their sedentary counterparts, but when their cholesterol levels were measured the exercising mice with a high-fat diet had worse lipid profiles. Both groups did see exercise-induced improvements in their levels of some inflammatory cytokines and c-reactive protein, which are thought to play a role in cardiovascular disease along with bad cholesterol and lipids.
“If you want to have an impact on cardiovascular disease, you need to do something about the culprit, which is high cholesterol – it leads to the formation of plaques that eventually cause atherosclerosis,” said Pascal J. Goldschmidt, M.D., Senior Vice President for Medical Affairs and Dean of the Miller School and one of the study’s authors. “If the goal of exercise is to reduce plaque formation, you must combine it with a good diet to get the desired results.”
Arthur Agatston, M.D., associate professor of medicine at the Miller School and the author of the South Beach Diet, designed the diet used in the study. Paul Kurlansky, M.D., of the Florida Heart Research Institute, helped plan and design the experiments.