Short-term consumption of a low-fat diet beneficially affects plasma lipid concentrations only when accompanied by weight loss. Hypercholesterolemia, low-fat diet, and plasma lipids.

Study subjects (6 women and 5 men) over the age of 40 years with fasting low-density lipoprotein cholesterol concentrations > 130 mg/dL were studied during three 5-week diet phases and one 10-week phase: baseline (36% fat: 13% saturated fatty acids [SFA], 12% monounsaturated fatty acids [MUFA], 8% polyunsaturated fatty acids [PUFA], and 128 mg cholesterol/1000 kcal); reduced fat (29% fat: 7% SFA, 9% MUFA, 11% PUFA, and 85 mg cholesterol/1000 kcal); and two low fat (15% fat: 5% SFA, 5% MUFA, 3% PUFA, and 73 mg cholesterol/1000 kcal). Body weight was maintained during the first three 5-week phases (baseline, reduced fat, and low fat [-->energy]) and decreased during the last 10-week phase when the low-fat diet was provided such that the subjects determined, in part, their caloric intake (low fat [decreases energy]). Mean body weight declined by 0.62 +/- 0.47 kg/wk during the first 5 weeks and 0.43 +/- 0.43 kg/wk during the second 5 weeks of the 10-week low-fat (decreases energy) period. Relative to the baseline diet, plasma cholesterol concentrations decreased from 226 +/- 33 to 195 +/- 19 (-13%), 208 +/- 22 (-7%), and 190 +/- 19 (-15%) mg/dL when the subjects consumed the reduced-fat, low-fat (--> energy), and low-fat (decreases energy) diets, respectively. Low-density lipoprotein cholesterol concentrations decreased from 158 +/- 28 to 128 +/- 16 (-18%), 134 +/- 17 (-14%), and 119 +/- 15 (-23%) mg/dL when the subjects consumed the reduced-fat, low-fat (--> energy), and low-fat (decreases energy) diets, respectively. High-density lipoprotein cholesterol concentrations decreased from 48 +/- 11 to 42 +/- 9 (-10%), 35 +/- 7 (-25%), and 38 +/- 8 (-18%) mg/dL when the subjects consumed the reduced-fat, low-fat (--> energy), and low-fat (decreases energy) diets, respectively. Triglyceride concentrations increased from 110 +/- 32 to 115 +/- 31 (8%), 188 +/- 76 (75%), and 130 +/- 32 (22%) mg/dL when the subjects consumed the reduced-fat, low-fat (--> energy), and low-fat (decreases energy) diets, respectively. Maximal changes in plasma lipid concentrations were observed after the first 5 weeks of the low-fat (decreases energy) diet phase despite continued weight loss throughout the entire 10-week diet period.(ABSTRACT TRUNCATED AT 400 WORDS)