STRATEGIES TO IMPROVE SKELETAL MUSCLE PROTEIN TURNOVER DURING DIETARY ENERGY RESTRICTION

Abstract

Weight loss through dietary energy restriction (ER) is an effective method to promote fat mass loss. However, a negative consequence of ER is the loss of lean body mass (LBM), particularly skeletal muscle, which is induced by an imbalance between rates of muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Increased protein intake and resistance exercise (RE) during ER promote the retention of LBM. Currently, the relative contribution of MPS and MPB to diet-induced LBM loss, and the effect of protein intake and RE on these variables is not well characterized. In Study 1 we compared the acute (hour-to-hour) MPS response to the ingestion of whey and soy protein, before and after 14 days of ER (-750kcal/d). The results of Study 1 indicated that whey protein was superior to soy protein in stimulating MPS before and after ER. In Studies 2 and 3 we examined the effect of 10 days of a marked 40% energy restriction on acute postabsorptive MPS and MPB and integrated (day-to-day) MPS. Using unilateral RE, we examined the effects of protein (1.2g protein/kg/g or 2.4g protein/kg/d) at rest and in combination with resistance exercise. The results of Study 2 showed that there were no changes in acute MPB or markers of proteolysis with ER. The results of Study 3 indicated that acute and integrated MPS were reduced following ER at both protein levels (1.2g protein/kg/g or 2.4g protein/kg/d), but RE was able to prevent this decline. Taken together, these studies demonstrate that reductions in MPS are the likely reason for LBM loss during short-term dietary energy restriction, and strategies such as RE and high quality protein intake can help to prevent the decline in MPS. These findings provide information for the design of weight loss programs that wish to preserve skeletal muscle.