Inflammation may affect benefits of low-fat, low-cholesterol diet

American Heart Association
Tuesday, 8 July 2003

People with a high level of C-reactive protein (CRP), a marker of inflammation in the body, don't receive the same beneficial reductions in cholesterol while on a low-fat, low-cholesterol diet as those with lower levels of CRP, according to a study in today's rapid access issue of Circulation: Journal of the American Heart Association.

"Not everyone appears to respond to a low-fat, low-cholesterol diet the same way, and we found that inflammation may have something to do with that," says Thomas P. Erlinger, M.D., M.P.H., of the Welch Center for Prevention, Epidemiology and Clinical Research at Johns Hopkins Medical Institutions in Baltimore.

"Until now, inflammation has been thought of as directly contributing to the risk of heart disease," he says. "Our findings, if true, suggest that inflammation may also indirectly increase heart disease risk by affecting the lipid response to dietary change. People with elevated CRP may be more resistant to the benefits of a healthy diet."

The study, conducted at Johns Hopkins University, analyzed a subset of participants in the Dietary Approaches to Stop Hypertension-Sodium (DASH-Sodium) trial. This trial included healthy adults who were not receiving antihypertensive medications and whose total cholesterol did not exceed 260 milligrams per deciliter (mg/dL).

Researchers followed 100 participants (ages 42 – 62) randomly assigned to the DASH diet or a control diet for 12 weeks. The DASH diet emphasizes fruits and vegetables, low-fat dairy products and other reduced fat foods. The fat make-up was 27 percent total fat and 6 percent saturated fat. The control diet had 37 percent total fat and 16 percent saturated fat. All participants followed the control diet for two weeks before being randomly switched to the DASH diet or continuing the control diet. Blood samples were taken before the participants were randomized to a diet and at the end of each 30-day period.

The diets kept each person's weight constant throughout the study.

The DASH diet resulted in significant reductions in total cholesterol, low-density lipoprotein (LDL or "bad" cholesterol) – and high-density lipoprotein (HDL or "good" cholesterol) levels. Levels of triglycerides didn't significantly change with the DASH diet.

In participants with baseline CRP levels below the median, the DASH diet reduced total cholesterol 9.8 percent and LDL cholesterol 11.8 percent. In participants with a baseline CRP above the average, reductions in total and LDL cholesterol were only 3 percent each.

In those with low baseline CRP, the DASH diet didn't significantly affect triglycerides. Conversely, triglycerides increased 19.8 percent among participants with high baseline CRP.

In participants with low CRP, differences in lipid responses to the DASH diet were evident by four weeks and persisted throughout the study.

The researchers emphasize that inflammation significantly and substantially affects the lipid response to a reduced-fat, low-cholesterol diet, with the greatest degree of lipid reduction seen in people with low CRP. The increase in triglycerides expected with more intake of carbohydrates, as occurs with the DASH diet, only occurred in people with elevated CRP.

If confirmed by other studies, the findings could have important implications for targeting people who are most likely to respond favorably to reduced-fat, low-cholesterol diets, Erlinger notes.

Even so, he adds, "We must caution that there is the possibility that we found a statistically significant association by chance. The relationship between lipids, diet and inflammation is very complex, and additional studies are really needed to confirm or refute our findings."

Overall, the DASH diet, when compared with the control, had no significant effect on CRP levels. This is in contrast with epidemiologic studies showing that diets similar to the DASH diet could reduce CRP levels. The researchers note that their findings suggest that previous associations of diet and CRP could be confounded by other unmeasured factors or by CRP-influencing factors like weight change.

Co-authors are Edgar R. Miller III, M.D., Ph.D.; Jeanne Charleston, R.N.; and Lawrence J. Appel, M.D., M.P.H. The National Institutes of Health and the National Heart, Lung, and Blood Institute funded the study.

For more information, or to contact American Heart Association, see their website at: www.americanheart.org