The effects of marked caloric restriction on lipoprotein lipase-activators in obese subjects

Abstract

Lipoprotein lipase plays a major role in the clearance of triglyceride rich lipoproteins, chylomicrons and very low density lipoproteins, from the circulation and also contributes to production of high density lipoproteins. To be functional lipoprotein lipase requires an activator which is present in the serum. Generally, serum triglyceride correlates positively with serum lipoprotein lipase-activator levels. During caloric restriction both serum triglyceride and adipose tissue liproprotein activity decrease. Affect of caloric restriction on serum lipoprotein lipase activator levels in not known. In this study we have evaluated the effect of marked caloric restriction on the levels of serum triglyceride, total cholesterol high-density lipoprotein cholesterol and lipoprotein lipase-activator in morbidly obese subjects. Initially, twenty subjects were included in the study. Twenty subjects consumed a 320kcal protein supplemented modified fast diet for three weeks, fourteen subjects for seven weeks and eight subjects for eleven weeks. Weight loss was continuous throughout the study. Serum triglycerides decreased during the first three weeks (Baseline 156±9 mg/dl, third week 119±9 mg/dl, p<0.01), followed by a plateau between third and fifth weeks and a small increase, from the fifth through the eleventh weeks. At eleven weeks serum triglycerides were not significantly lower than at the onset of caloric restriction. Serum total-cholesterol changed similarly showing a rapid and significant decline during the first five weeks, a plateau between fifth and seventh weeks and a small increase between ninth to eleventh weeks. However, at eleven weeks, serum cholesterol was significantly lower (Baseline 216±13 mg/dl, eleventh week 140±5 mg/dl, p<0.01). Serum high-density lipoprotein cholesterol level decreased significantly only in female subjects (Baseline 53±2 mg/dl, third week 37±2 mg/dl, p<0.01). Serum lipoprotein lipase-activator level increased steadily reaching approximately 200% of initial levels at week eleven (p<0.01). Thus, it appears that severe caloric restriction in morbidly obese subjects was associated with a significant decrease in the serum total cholesterol, a significant decrease in HDL-cholesterol in women. These decreases seen in serum lipids were limited to the first five weeks despite a continuous weight loss throughout this study. Serum lipoprotein lipase-activator level increased steadily and changes in serum lipoprotein lipase activator levels did not follow the changes in serum triglyceride levels during the caloric restriction.