It has become general knowledge that a high protein diet contributes to muscle mass raise and rapid weight loss. In this context, diets high in proteins and often restricted in carbohydrate intake are quite popular among overweight and obese subjects pursuing better weight and glycemic control strategies. However, this classical perception has been challenged, since increasing studies suggest that a high protein intake may not necessarily lead to accumulation of muscle protein. Therefore, seeking an effective nutritional strategy is extremely urgent.

Recently, a team of researchers from China Agricultural University, the Institute of Subtropical Agriculture, Chinese Academy of Sciences (ISA) conducted a study to investigate the effects of reduced dietary protein levels on protein metabolism and muscle growth, and the mechanisms underlying muscle protein deposition and myofiber development of the pigs.

The researchers found that moderately restricted protein diets (13% crude protein) improved the average daily gain, feed: gain ratio, and the weight of longissimus dorsi muscle (LDM) to the levels of the recommended adequate protein (AP) diets. Moreover, the mRNA abundance of myosin heavy chain I and genes related to muscle growth were upregulated, and the activation of mammalian target of rapamycin complex 1 (mTORC1) pathway was stimulated in LDM of growing-finishing pigs fed moderately restricted protein diets. These results suggest that the pigs fed moderately restricted protein diets could catch up to the growth performance and the LDM weight of the pigs fed the AP diets, and the underlying mechanism may be partly due to the alteration in energy status, modulation of muscle fiber characteristics and mTORC1 activation as well as its downstream effectors in skeletal muscle of different locations in growing-finishing pigs.

The research was the jointly supported by the National Basic Research Program of China (2013CB127305), the Nature Science Foundation of Hunan Province (S2014J504I), the Major Project of Hunan Province (2015NK1002) and the National Science and Technology Ministry (2014BAD08B11).

The study entitled "Effects of dietary protein restriction on muscle fiber characteristics and mTORC1 pathway in the skeletal muscle of growing-finishing pigs" has been published in Volume 7, issue 1, August 2016 of Journal of Animal Science and Biotechnology, details could be found at https://doi.org/10.1186/s40104-016-0106-8.