Study of Macronutrients and Heart Disease Risk (MACRO)

The objective of this trial is to examine the long-term effects of a diet low in carbohydrates, as compared to one low in fat, on cardiovascular disease risk factors, including blood pressure (BP), body weight and composition, serum lipids, plasma glucose, insulin, adipocytokines (adiponectin, leptin, resistin), and C-reactive protein (CRP) among obese adults.

The investigators will test the following hypotheses:

Hypothesis 1: Compared to a low fat diet, a diet low in carbohydrates will reduce systolic and diastolic BP over 12 months; Hypothesis 2: Compared to a low fat diet, a diet low in carbohydrates will reduce body weight, total percent body fat, and waist circumference over 12 months; Hypothesis 3: Compared to a low fat diet, a diet low in carbohydrates will reduce serum levels of LDL-cholesterol and triglycerides and increase serum levels of HDL-cholesterol over 12 months; Hypothesis 4: Compared to a low fat diet, a diet low in carbohydrates will reduce plasma levels of glucose and insulin levels over 12 months; and Hypothesis 5: Compared to a low fat diet, a diet low in carbohydrates will reduce plasma levels of leptin, resistin, and CRP and increase plasma levels of adiponectin over 12 months.

Cardiovascular diseases (CVD) remain the leading cause of death globally as well as here in the United States. Manipulations of the macronutrient (protein, carbohydrate and fat) contents of diet have been used extensively for weight loss and weight control in the past several decades. Low carbohydrate diets, in particular, have gained popularity for weight loss. However, few studies have examined the effects of a diet low in carbohydrates on traditional and novel cardiovascular risk factors in the long term, particularly in contrast to the current dietary recommendations for decreased fat intake to reduce risk of CVD. In this proposal, we plan to conduct a 12-month, parallel-arm, randomized controlled trial of a diet low in carbohydrates versus the currently recommended low fat diet to reduce CVD risk factors among obese adults. The objective of this trial is to examine the long-term effects of a diet low in carbohydrates, as compared to one low in fat, on CVD risk factors, including blood pressure (BP), body weight and composition, serum lipids, plasma glucose, insulin, adipocytokines (adiponectin, leptin, resistin), and C-reactive protein (CRP) among obese adults. In order to accomplish these objectives we will randomize 130 eligible participants (n=65 in each group) to consume either a diet low in carbohydrates (≤40 g/d) or a diet low in fat (<7% saturated fat, <30% total fat). Neither of the diets will be energy-restricted. Participants will meet with a dietitian for one-on-one counseling sessions weekly for the first 4 weeks, then bi-monthly in small group sessions for the next 5 months, and monthly in larger group sessions for the final 6 months of the intervention. Data on both traditional and novel CVD risk factors will be collected at baseline, 3, 6, and 12 months. We hypothesize that a diet low in carbohydrates as compared to a diet low in fat will lower systolic and diastolic BP, body weight, total percent body fat, waist circumference, serum levels of triglycerides, and plasma levels of insulin, glucose, leptin, resistin, and CRP, and increase serum levels of HDL-cholesterol and adiponectin. Because CVD is the most common cause of death here in the U.S. and world-wide, this study has important public health implications. It will provide new information on the potential long-term effects of diets low in carbohydrates on both the traditional risk factors for CVD as well as novel risk factors and inflammatory factors. The results from this study will help to determine if a diet low in carbohydrates as compared to the currently recommended low fat diet can decrease the risk of CVD among obese adults.