The use of low fat, high-carbohydrate (CHO)1 diets as a primary strategy to prevent cardiovascular disease has been challenged recently because of their potentially undesirable impact on plasma triglyceride (TG) and high-density lipoprotein cholesterol (HDL-C) concentrations (1) . It must be stressed that most studies that have highlighted these undesirable effects of high-CHO diets on plasma lipids were carried out under isocaloric conditions where caloric intake was imposed to keep body weight constant (2) . Another element that has led to increasing concern that high-CHO diets may not represent the optimal diet to prevent obesity and cardiovascular complications is that over the last 20 years, the reduction in fat intake in North America has been paralleled by a paradoxical increase in the prevalence of obesity (1) (3) . However, it must be noted that CHO quality [simple vs. complex or with a high vs. low glycemic index (GI)] may induce different metabolic responses and should be taken into account when evaluating the impact of high-CHO diets on the health profile. Indeed, the ad libitum consumption of high-complex CHO diets, which generally leads to significant reductions in body weight (4) (5) , has also been associated with highly desirable improvements in the cholesterol profile (6) (7) . What remains unclear is the extent to which these changes associated with high-CHO diets are dependent on concurrent reductions in body weight. The long-term compliance to high-complex CHO diets has also been an issue of concern in the free-living state because of the lower palatability of high-complex CHO diets compared with high-fat foods (8) (9) .
In that context, diets rich in monounsaturated fatty acids (MUFAs) (high-MUFA diets) have been advocated as dietary alternatives with good long-term compliance to prevent cardiovascular disease. In trials conducted under isocaloric conditions, high-MUFA diets have been reported to lower plasma low-density lipoprotein cholesterol (LDL-C) and TG concentrations with no undesirable effect on HDL-C levels (10) . However, due to the high caloric density of lipids, the effects of high-fat diets on weight management remain controversial. Several studies have reported that high-fat diets may promote body fat accumulation, which may in turn perpetuate a deteriorated lipid profile (11) (12) (13) . It must be stressed that very little is known about the impact of ad libitum consumption of high-fat diets rich in MUFA on body weight and on the plasma lipid profile. It is also unclear how changes in the lipid profile induced by such diets are a function of variations in body weight in ad libitum conditions.
Therefore, the objectives of this study were to compare the effects of ad libitum consumption of a diet rich in complex CHO vs. a high-fat diet rich in MUFA on body weight and body fat distribution in men and to examine the extent to which diet-induced variations in body weight and body fat distribution modulate the diet-induced changes in plasma lipid levels.