High protein diets enhance body composition in rats: a comparative analysis of milk‐and soy‐based energy restricted diets

Abstract

Consuming high protein diets during energy restriction may protect muscle health. However, the extent to which protein source modulates muscle responses to energy restriction is not well described. Eighty male Sprague‐Dawley rats (12 weeks old) were randomly divided into 8 treatment groups and fed energy adequate (EA) and energy restricted (ER; 60% of the ad libitum feed intake for EA) diets containing two levels (control protein: CP, 10%; and high protein: HP, 35%) and sources (milk protein concentrate: MPC; and isoflavone‐free soy isolate: SOY) of protein for 16 weeks. Body mass was assessed weekly, and fat (FAT) and fat‐free mass (FFM), as percentages of total body mass were determined on weeks 0 and 16 using dual energy x‐ray absorptiometry. Body mass was similar for all rats on week 0, and increased (P < 0.05) linearly independent of protein level and source. Subsequent to week 0, body mass was lower for ER compared to EA (energy‐by‐time, P < 0.05). Protein level influenced FAT and FFM independent of protein source and energy, as FAT was lower and FFM was higher at week 16 for HP compared to CP (P < 0.05). Regardless of protein level and source, FAT was lower and FFM was higher at week 16 for ER than EA (P < 0.05). These data suggest consuming a HP diet may spare FFM and improve body composition independent of energy status, although skeletal muscle responses to milk‐and soy‐based diets are likely comparable. Supported by Dairy Research Institute and USAMRMC