Energy restriction only slightly influences protein metabolism in obese rats, whatever the level of protein and its source in the diet

Abstract

BACKGROUND: High protein (HP) diets during energy restriction have been studied extensively regarding their ability to reduce body fat and preserve lean body mass, but little is known about their effects on protein metabolism in lean tissues. OBJECTIVE: To determine the effects of energy restriction and protein intake on protein anabolism and catabolism in rats. METHODS: For 5 weeks, 56 male Wistar rats were fed an obesity induction (OI) diet . They were then subjected to a 40% energy restriction using the OI diet or a balanced HP diet for 3 weeks, whereas a control group was fed the OI diet ad libitum (n ¼ 8 per group). HP-restricted rats were divided into five groups differing only in terms of their protein source: total milk proteins, casein (C), whey (W), a mix of 50% C and W, and soy (n ¼ 8). The animals were then killed in the postprandial state and their body composition was determined. Protein synthesis rates were determined in the liver, gastrocnemius and kidney using a subcutaneous 13 C valine flooding dose. mRNA levels were measured for key enzymes involved in the three proteolysis pathways. RESULTS: Energy restriction, but not diet composition, impacted weight loss and adiposity, whereas lean tissue mass (except in the kidney) was not influenced by diet composition. Levels of neoglucogenic amino acids tended to fall under energy restriction (Po0.06) but this was reversed by a high level of protein. The postprandial protein synthesis rates in different organs were similar in all groups. By contrast, mRNA levels encoding proteolytic enzymes rose under energy restriction in the muscle and kidney, but this was counteracted by a HP level. CONCLUSIONS: In adult obese rats, energy restriction but not diet composition affected fat pads and had little impact on protein metabolism, despite marked effects on proteolysis in the kidney and muscle.

Metabolomic analysis reveals distinct profiles in the plasma and urine of rats fed a high-protein diet

“…In agreement with previous studies (Chevalier et al 2013;Jean et al 2001;Lacroix et al 2004), our research demonstrated some hyperproteic dietrelated changes, including persistent weight loss and lower food intake, an obvious reduction of plasma triglyceride and adipose tissue weight, and a decrease of plasma glucose and insulin in HPLC compared to MPMC rats. Thus, these parameters could be seen as phenotypes that can provide a reference for the application of nutrient interventions by protein supplement against hyperglycemia and hypercholesteremia.…”

High-protein diet selectively reduces fat mass and improves glucose tolerance in Western-type diet-induced obese rats

“…Many studies have characterized the feeding-suppressive effect of a high-protein diet in rats starting the first day with a gradual adaptation during the following days (4,6,28,32). However, less is known on the efficacy of a high-protein diet to curtail spontaneous energy intake in diet-induced obese rats, as studies were set mainly in the context of an additional 40% energy restriction (1,12,18), making it difficult to analyze the respective contributions of these interventions. In the current study, the shifting from a 20% to a 52% protein diet markedly reduced the daily energy intake on the first day by 41% and 31% in the standard diet and DIO group, respectively.…”

“…3A). During the remaining observation period (days [2][3][4][5][6][7][8][9][10][11][12][13][14], rats in the standard diet/standard diet group displayed an overall stable food intake with an average of 67.6 Ϯ 1.0 kcal/day (Fig. 3A).…”

Beneficial Effects of an Amino Acid Mixture on Colonic Mucosal Healing in Rats

“…42 13 C-valine enrichment in free and protein-bound amino acids, respectively, was determined as described previously. 42,43 Fractional synthesis rate (FSR, %/d) of colon protein was calculated as FSR ¼ Ebound val/(Efree val · t) · 100, where Ebound val and Efree val are the protein-bound and free 13 C-valine enrichments in the colon. Absolute synthesis rates (ASR, g/d) were calculated as ASR ¼ FSR · P, where P is colon protein content.…”