Context: The long-term effect of aggressively vs moderately fat-restricted diets has not been studied extensively in free-living subjects with different types of hyperlipidemia.
Objective: To compare the cholesterol-lowering effects of 4 levels of dietary fat intake restriction after 1 year.
Design: Randomized, parallel, comparison trial.
Setting: Male employees of a large industry.
Participants: A total of 444 men had low-density lipoprotein cholesterol (LDL-C) levels above the 75th age-specific percentile. Subjects with triglyceride (TG) levels less than the 75th age-specific percentile were defined as hypercholesterolemic (HC) and those with TG levels at or above the 75th age-specific percentile were defined as combined hyperlipidemic (CHL).
Interventions: Hypercholesterolemic subjects were randomized to diets 1, 2, 3, and 4 taught to contain 30%, 26%, 22%, and 18% fat, and the CHL subjects were randomized to diets 1, 2, and 3. All 4 diets were taught to subjects and spouses or partners in 8 weekly 2-hour classes.
Main outcome measures: Plasma lipoprotein levels after 1 year.
Results: Fat intake after 1 year declined from a mean of 34% to 36% of energy to 27%, 26%, 25%, and 22% in the 4 HC diet groups and 28%, 26%, and 25% in the 3 CHL diet groups. Mean+/-SD percent LDL-C reductions were 5.3%+/-16.2%, 13.4%+/-12.6%, 8.4%+/-11.2%, and 13.0%+/-15.7% in the HC diet groups and 7.0%+/-16.2%, 2.8%+/-15.8%, and 4.6%+/-13.5% in the CHL diet groups (P<.01 in all but 1 instance). Apoprotein B levels decreased 8.6%, 10.7%, 4.3%, and 5.3% in the HC groups and 14.6%, 11.4%, and 9.9% in the CHL groups (P<.05-.01 in each instance). Triglyceride levels increased significantly in subjects following HC diets 3 and 4, 21.7% and 38.7% (P<.05 and .01), but not in any CHL subjects. High-density lipoprotein cholesterol decreased 2.8% and 3.2% in subjects on HC diets 3 and 4, respectively (P<.05 in both cases).
Conclusions: After 1 year, moderate restriction of dietary fat intake attains meaningful and sustained LDL-C reductions in HC subjects and apoprotein B reductions in both HC and CHL subjects. More extreme restriction of fat intake offers little further advantage in HC or CHL subjects and potentially undesirable effects in HC subjects.