Kirsten Hilpert, doctoral candidate in the nutrition option of Penn State's Integrative Biosciences program, conducted a small study of the Step 1 diet's effect on men and women with moderately elevated cholesterol. She found that those who also had elevated CRP levels couldn't lower their LDL-cholesterol numbers with the Step 1 cholesterol-lowering diet, even when soy protein, a food with an approved FDA heart health claim, was added to the diet.
The National Cholesterol Education Program Step 1 diet, the first level of treatment for high cholesterol, is a low fat diet that restricts total fat to 30 percent of calories with saturated fat less than 10 percent.
Hilpert notes, "Although there are specific dietary factors, like soy, that have been shown to lower blood cholesterol, not all people experience this benefit. Our study suggests that if your CRP is elevated, you may not be able to reap the full benefit of the Step 1 Diet with or without soy."
The study is detailed in a paper, Lipid Response to a Low-Fat Diet with or without Soy Is Modified by C-Reactive Protein Status in Moderately Hypercholesterolemic Adults, published in a recent issue of the Journal of Nutrition. Hilpert's co-authors are Dr. Penny Kris-Etherton, distinguished professor of nutrition, and Dr. Sheila West, assistant professor of biobehavioral health.
Hilpert points out that in recent studies other researchers noticed that only individuals with low CRP levels experienced significant reductions in total cholesterol when consuming the DASH diet, a low-fat, low sodium diet shown to reduce high blood pressure.
The Penn State researchers decided to see if CRP status had the same effect when subjects consumed a cholesterol-lowering diet. Their study is among the first to test whether or not CRP status can predict a person's lipid response to a cholesterol-lowering diet including soy.
They recruited 32 older, overweight people with moderately elevated cholesterol. The participants included 14 men and 18 women, six of whom were receiving hormone replacement therapy. Their LDL cholesterol was in the 124 to 211 mg/dl range.
For three weeks, each participant ate only foods on the National Cholesterol Education Program Step 1 diet prepared in the research kitchen. For the next six weeks, they were fed the Step 1 diet plus 25 grams of soy protein or milk protein, after which their blood samples were drawn. The participants then took a two-week break and ate their usual diet before returning to eating only foods from the research kitchen.
In the final 6 weeks of the study, the participants again ate the Step 1 diet with either soy or milk protein added. Those that had had soy protein in the earlier 6-week phase received milk protein and vice versa, after which their blood samples were drawn again.
Analysis of the participants' blood samples showed that the Step 1 diet only lowered LDL-cholesterol in people with low CRP levels. LDL-cholesterol levels in those who had elevated CRP were, in fact, increased even further as the result of the diet. Adding soy or milk protein to the Step 1 diet did not affect either cholesterol or CRP levels.
Hilpert says, "These results suggest that habitual consumption of a Step 1 diet may beneficially affect individuals with CRP levels less than 3.5 mg/L, the median level of the study, and may have deleterious effects in patients with elevated levels. "
She adds, "If these results are confirmed in other studies, the next question is whether lowering CRP will improve diet response."
Funding from the Protein Technologies International, now known as The Solae Company, supported the study.
Journal
Journal of Nutrition