Most people must eat meat every day, especially in the meat-hungry west. However, what do people eat when they eat meat? From a health perspective, a low intake of saturated fat and increased ratio of polyunsaturated fatty acid (PUFA) to saturated fatty acid (SFA) in meat/muscle are associated with a lower risk of cardiovascular and metabolic disorders. Therefore, providing meat with superior quality and nutritional value is an important goal for human health.

Branched-chain amino acid (BCAA), including leucine (Leu), isoleucine (Ile), and valine (Val), cannot be synthesized endogenously in the body and need to be provided by the diet. They exert several critical roles in metabolism homeostasis and cell functions including energy homeostasis and lipid metabolism regulation. A good knowledge of the effects of BCAAs on regulating the fat content and fatty acid composition within muscle would help improve eating quality and nutritional value of the meat and consequently improve the health status of humans.

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 low-protein diets (17% crude protein, CP ) supplemented with different BCAA ratios on the intramuscular fat (IMF) content and fatty acid composition in different location of skeletal muscles, including the longissimus dorsi, biceps femoris (BF), and psoas major muscle of growing pigs, and also examined the mRNA expression levels of genes involved in lipid metabolism in these muscle tissues.

The researchers found that a low-protein diet (17% CP) with an effect of BCAA ratio (Leu:Ile:Val = 1:0.25:0.25-1:0.75:0.75) could increase the IMF content in BF muscle, and raise the ratio of PUFA to SFA but decrease the n-6:n-3 PUFA ratio in different skeletal muscles compared with adequate protein diet (20% CP). This effect was associated with the altered mRNA expression level of genes involved in lipid metabolism, which facilitated the absorption and utilization of fatty acids in the muscle tissues. This would be helpful to supply high-quality meat for humans.

The research was the jointly supported by National Basic Research Program of China (2013CB127305, 2012CB124704), National Nature Science Foundation of China (31110103909, 31330075), Youth Innovation Promotion Association CAS (2015), Nature Science Foundation of Hunan Province (2015JJ2146), and The Chinese Academy of Science STS Project (KFJ-EW-STS-063).

The study entitled "Effects of supplementation with branched-chain amino acids to low-protein diets on expression of genes related to lipid metabolism in skeletal muscle of growing pigs" has been published in Amino Acids, details could be found at http://dx.doi.org/10.1007/s00726-016-2223-2.