Losing fat while gaining muscle is generally considered the holy grail of dieting. Unfortunately, the vast majority of weight loss studies show that as much as 20-30% of the body weight lost during dieting is from lean body mass (including muscle mass). Maintenance of muscle mass is important for everyone, but becomes particularly relevant when athletes are trying to lose weight while improving performance, as well as for older adults due to the importance of muscle mass for overall health and mobility.
Resistance training is one of the most important factors for maintaining muscle mass while dieting, with other major ones shown in Figure 1. It can attenuate the loss of muscle by stimulating muscle protein synthesis (MPS). And it’s also been well established that protein supplementation can augment the effects of strength training on MPS. However, the optimal protein intake to promote weight loss while retaining and/or increasing muscle mass has yet to be firmly determined.
Reference: Atherton et al. J Physiol. 2012 Mar.Being in an energy deficit appears to reduce basal MPS, as well as the sensitivity of MPS from feeding. However, a resistance training program along with increased protein intake can synergistically increase rates of MPS. This is particularly valuable during an energy deficit, as one study showed consuming 30 grams of protein after resistance exercise led to a greater stimulation of MPS than the consumption of 15 grams of protein. Another study found that 1.6 grams of protein per kilogram of bodyweight (2x the Recommended Dietary Allowance, or RDA) was able to reduce the loss of lean body mass during energy restriction, while yet another study suggested that more than two grams per kilogram of bodyweight may be needed to maintain lean mass when dieting.
Beyond resistance training, high-intensity interval training during a calorie deficit can also help to retain lean mass. A further consideration is the effects of an energy deficit on hormone levels, with or without exercise. Hormones such as IGF-1 and testosterone may play a role in the maintenance of lean mass during an energy deficit combined with physical activity, though this remains somewhat of an open question.
With questions still remaining about the optimal protein intake and exercise regimens during an energy deficit, researchers designed a four-week study with participants undergoing an approximate 40% caloric reduction along with daily resistance or interval training, while consuming either moderate or higher protein intakes of 1.5x and 3x the RDA for protein. Changes in body composition, hormone levels, and indices of strength and aerobic capacity were measured. Unfortunately, measures of metabolic rate were not made either before or after the intervention.
Retention of lean body mass is important when dieting. Increased protein intake and resistance training can help preserve lean mass during a calorie deficit. This study was set up to test two different protein intakes consumed by people in a caloric deficit and following a daily exercise program.