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, suggest results of a Johns Hopkins study.
According to the study's results, published in Circulation, measuring circulating blood levels of C-reactive protein (CRP) - 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 P. Erlinger, assistant professor of medicine at the Johns Hopkins' Welch Center for Prevention, Epidemiology and Clinical Research, 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.
The researchers recorded a nearly 10 per cent drop in total cholesterol and nearly 12 per cent reduction in LDL cholesterol for subjects with lower CRP readings at the start of the study (less than 2.37 milligrams per litre). Their triglycerides were not affected. Meanwhile, in those with higher CRP levels (more than 2.37 mg/L), total and LDL cholesterol were lowered by only 3 per cent each, while triglycerides rose by 19 per cent.
However, 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 favourable response to a reduced-fat, low-cholesterol diet from those who will not respond well,"said 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 per cent total fat and 16 per cent saturated fat, participants were assigned to continue to follow either the control diet or the DASH diet, which contains 27 per cent total fat and 6 per cent 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.
Further details of the study can be found in the 15 July issue of the journal Circulation.