Results of a Johns Hopkins study suggest that natural chemicals released in the body as a result of chronic inflammation may underpin the failure of low-fat, so-called heart healthy diets to actually reduce cholesterol and heart disease risk in some people.
According to the study's results, published in the July 15 issue of Circulation, measuring circulating blood levels of C-reactive protein — a marker of inflammation already linked to increased risk of heart disease — may predict who might benefit from a reduced-fat, low-cholesterol diet and who might not.
For the study, a team led by Thomas "Tate" P. Erlinger, M.D., M.P.H., assistant professor of medicine, tracked 100 subjects with elevated CRP levels following a reduced-fat, low-cholesterol diet for 12 weeks. They found that overall, this group had less of a reduction in total cholesterol and low-density lipoprotein (LDL) or "bad" cholesterol levels. Subjects also had a greater increase in triglycerides compared with another group on the same diet but with lower CRP levels.
Subjects with lower CRP readings at the start of the study (less than 2.37 milligrams per liter) had a nearly 10 percent drop in total cholesterol and nearly 12 percent reduction in LDL cholesterol. Their triglycerides were not affected. In those with higher CRP (more than 2.37 mg/L), total and LDL cholesterol were lowered by only 3 percent each, while triglycerides rose by 19 percent.
Erlinger cautions that the study sample was small and did not examine the impact of weight loss on CRP levels.
"An important implication of our findings is that we may be able to use CRP testing to distinguish those who are likely to have a favorable response to a reduced-fat, low-cholesterol diet from those who will not respond well," says Erlinger. "It may also help explain why different people on the same diet may have widely varying results. It's too early for broad recommendations, but additional research in this area could help physicians tailor diets for specific patients."
While causes of inflammation vary, the condition itself has already been linked to several cardiovascular risk factors including hypertension, diabetes and elevated triglycerides. CRP has recently been identified — along with cigarette smoking and obesity — as a risk factor for cardiovascular disease.
The 100 healthy adults in the study had an average age of 52 and already were participating in the national Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial.
The Hopkins team took blood samples from each participant at the study's start to measure CRP, cholesterol and triglycerides. After two weeks on a control diet of 37 percent total fat and 16 percent saturated fat, participants were assigned to continue to follow either the control diet or the DASH diet, which calls for 27 percent total fat and 6 percent saturated fat, for 12 weeks.
The study was supported by grants from the National Institutes of Health, the National Heart, Lung and Blood Institute and the General Clinical Research Center at Johns Hopkins. Co-authors were Edgar R. Miller III, M.D., Ph.D.; Jeanne Charleston, R.N.; and Lawrence J. Appel, M.D., M.P.H.
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Erlinger, Thomas P. et al, "Inflammation Modifies the Effects of a Reduced Fat, Low Cholesterol Diet on Lipids: Results from the DASH-Sodium Trial," Circulation, July 15, 2003; Vol. 108, pages 150-154.
Johns Hopkins' Welch Center for Prevention, Epidemiology and Clinical Research http://www.med.jhu.edu/welchcenter/
Information on the DASH diet http://www.nhlbi.nih.gov/health/public/heart/hbp/dash/
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