RELATIVE EFFECTS OF WEIGHT-LOSS AND DIETARY-FAT MODIFICATION ON SERUM-LIPID LEVELS IN THE DIETARY-TREATMENT OF OBESITY

The independent effects of weight loss and dietary fat modification on serum lipids were investigated in two groups of healthy moderately ob ese men and women. In one group (sequential group, n - 19), a weight-s table low-fat, low-saturated-fat diet (Low-Sat) was given for 7 weeks (= dietary modification), followed by a 4.2 MJ/day deficit Low-Sat die t for 13 weeks (i.e., weight loss alone). Another group (simultaneous group, n=22) received a 4.2 MJ/day deficit Low-Sat diet for 13 weeks ( i.e., weight loss + dietary fat modification). Each group was subject to an initial weight-stable high-fat, high-saturated fat diet for 3 we eks and a final weight stable Low-Sat diet for 3 weeks. Both groups lo st similar amounts of body weight, about 13 kg, and had similar overal l changes in total cholesterol, low density lipoprotein (LDL), cholest erol, high density lipoprotein (HDL) cholesterol, the HDL/LDL ratio, a nd triglycerides. Analysis of the separate effects of the Low-Sat diet without energy restriction and of weight loss in the sequential group showed that weight loss per se was responsible for about 50% of the t otal reduction in total cholesterol, and for about 60% and 70% of the fall in LDL cholesterol and triglycerides, respectively. Fat modificat ion without weight loss reduced HDL cholesterol by 11.1% and the HDL/L DL ratio by 7.7%, while weight loss per se led to increases in HDL cho lesterol of 12.5% and in the HDL/LDL ratio of 24.0%. We conclude that the effects of reduction in fat and saturated fat intake and weight lo ss are additive. The net favorable effect of weight loss seems to be g reater than that of dietary fat modification in optimizing the serum l ipid profile of obese subjects.