Submitted to: American Journal of Physiology - Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2007
Publication Date: 9/18/2007
Citation: Afolabi, P.R., Jahoor, F., Jackson, A.A., Stubbs, J., Johnstone, A.M., Faber, P., Lobley, G., Gibney, E., Elia, M. 2007. The effect of total starvation and very low energy diet in lean men on kinetics of whole body protein and five hepatic secretory proteins. American Journal of Physiology - Endocrinology and Metabolism. 293:E1580-E1589. Interpretive Summary: Because of the current obesity problem there are several weight loss programs. Some advocate rapid weight loss with very low calorie diets or total starvation, while others advocate a more gradual weight loss with diets that only restrict calorie intake moderately. It is believed that physical, psychological, and metabolic functions are affected to a greater extent when the rate of weight loss is rapid than when the same amount of weight loss occurs more slowly. Little attention has been given to the possibility that the rate of weight loss, determined by the extent of dietary restriction, may have major effects on the body's metabolism, independent of the amount of weight loss. One important question is how different rates of weight loss will affect the blood proteins that are responsible for the transport of hormones, drugs, and nutrients such as fats, vitamins and minerals, and also other blood proteins that assist in fighting off infections. In this study we examined the effect of 5% loss of body weight induced either rapidly (5 days) through total starvation (starvation group), or more slowly with a very low energy diet (VLED group), on how fast the body makes and breaks down all body proteins and the rate at which it makes several different blood proteins. The study was performed in two groups of normal weight men. The starvation group showed greater increases in whole body protein loss but made most of the blood proteins at a faster rate. It is concluded that normal weight men lose more body protein during rapid weight loss and make blood proteins at a faster rate that is closely related to the rate than to the magnitude of weight loss.
Technical Abstract: It is unclear whether the rate of weight loss, independent of magnitude, affects whole body protein metabolism and the synthesis and plasma concentrations of specific hepatic secretory proteins. We examined 1) whether lean men losing weight rapidly (starvation) show greater changes in whole body protein kinetics, synthesis, and circulating concentrations of selected hepatic secretory proteins than those losing the same amount of weight more slowly [very low energy diet (VLED)]; and 2) whether plasma concentrations and synthetic rates of these proteins are related. Whole body protein kinetics were measured using [1-(13)C]leucine in 11 lean men (6 starvation, 5 VLED). Fractional and absolute synthetic rates of HDL-apolipoprotein A1 (apoA1), retinol binding protein, transthyretin, alpha(1)-antitrypsin (alpha(1)-AT), and transferrin were measured using a prime-constant intravenous infusion of [(13)C(2)]glycine. Compared with VLED group, the starvation group showed greater increases (at a 5% weight loss) in whole body protein oxidation (P < 0.05); fractional synthetic rates of HDL-apoA1 (25.3 vs. -1.52%; P = 0.003) and retinol binding protein (30.6 vs. 7.1%; P = 0.007); absolute synthetic rates of HDL-apoA1 (7.1 vs. -3.8 mg.kg(-1).day(-1); P = 0.003) and alpha(1)-AT (17.8 vs. 3.6 mg.kg(-1).day(-1); P = 0.02); and plasma concentration of alpha(1)-AT (P = 0.025). Relationships between synthetic rates and plasma concentrations varied between the secreted proteins. It is concluded that synthetic rates of hepatic secreted proteins in lean men are more closely related to the rate than the magnitude of weight loss. Changes in concentration of these secreted proteins can occur independently of changes in synthetic rates, and vice versa.