To compare the effects on blood pressure and plasma lipids of three different diets--a carbohydrate-rich diet, a protein-rich diet, or a diet rich in unsaturated fat.

BACKGROUND:

While there is widespread consensus that the optimal diet to reduce cardiovascular risk should be low in saturated fat, the type of macronutrient that should replace saturated fat (carbohydrate, protein or unsaturated fat) is a major, unresolved research question with substantial public health implications. The study will evaluate these three dietary approaches by studying their effects on established coronary risk factors and a selected group of emerging risk factors.

DESIGN NARRATIVE:

The study design was a randomized, three period cross-over feeding study that compared the effects on blood pressure and plasma lipids of a carbohydrate-rich diet patterned after the DASH diet (CARB) to two other diets, one rich in protein (PROTEIN) and another rich in unsaturated (UNSAT) fat, predominantly monounsaturated fat. The DASH diet has been shown to reduce blood pressure and LDL-cholesterol substantially, and is currently recommended by policy makers. During a one week run-in, all participants were fed samples of the three study diets (CARB, PROTEIN and UNSAT). Using a three period cross-over design, participants were then randomly assigned to the CARB, PROTEIN or UNSAT diet. Each feeding period lasted six weeks; a washout period of at least two weeks separated each feeding period. Throughout feeding (run-in and the three intervention periods), participants were fed sufficient calories to maintain their weight. Trial participants were 30 years of age or older, with systolic blood pressure of 120-159 mmHg or diastolic blood pressure of 90-99 mmHg. Primary outcomes variables were blood pressure and the established plasma lipid risk factors (LDL-C, HDL-C and triglycerides). Secondary outcomes include total cholesterol, apolipoproteins VLDL-apoB, VLDL-apoCIII, apolipoprotein B, non-HDL cholesterol, and lipoprotein(a).

Inclusion criteria:

• Healthy adults
• Aged 30 years and older
• Systolic blood pressure of 120 to 159 mm Hg or a diastolic blood pressure of 80 to 99 mm Hg.

Exclusion criteria:

• Diabetes
• Active or prior Cardiovascular disease (CVD)
• LDL cholesterol greater than 220 mg/dL (>5.70 mmol/L)
• Fasting triglycerides greater than 750 mg/dL (>8.48 mmol/L)
• Weight more than 350 lb (>159 kg)
• Taking medications that affect blood pressure or blood lipid levels
• Unwillingness to stop taking vitamin and mineral supplements
• Alcoholic beverage intake of more than 14 drinks per week.

Outcome assessors were unaware of diet sequence.