Effect of protein and methionine intakes on plasma homocysteine concentrations: a 6-mo randomized controlled trial in overweight subjects

Abstract

A high plasma homocysteine concentration is an independent risk factor for cardiovascular disease. Homocysteine concentrations are thought to be raised by high protein and methionine intakes. Our goal was to investigate the effects of high and low protein and methionine intakes on homocysteine in overweight subjects. Sixty-five overweight subjects were randomly assigned to a 6-mo intervention with a low-protein, low-methionine diet (LP: 12% of total energy, 1.4 g methionine/d; n = 25); a high-protein, high-methionine diet (HP: 22% of total energy, 2.7 g methionine/d; n = 25), both of which had similar fat contents (30% of total energy); or a control diet with an intermediate protein content (n = 15). All food was self-selected at a shop at the department. Protein intake was increased in the HP group mainly through lean meat and low-fat dairy products. Dietary compliance was evaluated by urinary nitrogen excretion. Homocysteine concentrations did not change significantly in the LP or control groups but were 25% lower in the HP group (NS). Homocysteine concentrations after the 3-mo intervention were inversely associated with vitamin B-12 intake and with weight change (by multivariate analysis performed for all subjects), but not with methionine or protein intake. Sixty-nine percent of the variation could be explained by baseline homocysteine (P < 0.001), 2% by vitamin B-12 (P = 0.02), and another 2% by weight change (P = 0.06). The plasma homocysteine concentration after 6 mo was associated only with baseline homocysteine (P < 0.001). A high-protein, high-methionine diet does not raise homocysteine concentrations compared with a low-protein, low-methionine diet in overweight subjects.