Divergent intramuscular mTORC1 signaling responses to habitual consumption of milk‐and soy‐based energy restricted diets

Abstract

The effects of milk‐or soy‐based, high‐protein, energy restricted (ER) diets on intracellular regulators of muscle mass are not well described. Eighty male Sprague‐Dawley rats were randomly divided into groups and fed energy adequate (EA) and ER (60% of average ad libitum EA feed intake) diets containing two protein sources (milk protein concentrate: MPC; or isoflavone‐free soy isolate: SOY) and levels (control protein: CP, 10%; high protein: HP, 35%) for 16 weeks. Basal protein expression and phosphorylation of mammalian target of rapamycin complex 1 (mTORC1) associated proteins were assessed using multiplex. Phosphorylation of mTOR was lower (P < 0.05) for ER compared to EA. Independent of protein level, p70S6K1 expression was lower (P < 0.05) for ER MPC compared to EA MPC. However, mTOR and rpS6 protein expression were higher (P < 0.05) for ER SOY than ER MPC, and TSC2, mTOR, and rpS6 were higher (P < 0.05) for ER SOY compared to EA SOY. Phosphorylation of rpS6 was also higher (P < 0.05) for EA SOY compared to EA MPC, and p70S6K1 phosphorylation was higher (P < 0.05) for SOY versus MPC, regardless of energy status and protein level. These data demonstrate divergent mTORC1 responses to soy‐and milk‐based energy restricted diets but suggest that habitual consumption of soy‐based diets may enhance protein synthetic responses to feeding by upregulating the expression of key mTORC1 signaling proteins. Supported by Dairy Research Institute and USAMRMC