The small study sought to assess the effects of a high-protein diet enriched with BCAA on whole-body protein kinetics as well.
“Insulin resistance is one of the critical factors for the cause-effect relationship between the physical inactivity-related sedentary lifestyle and the metabolic syndrome,” the Italian researchers wrote. “The latest includes abnormalities of lipid pattern, arterial hypertension, increased glycemia and endothelial dysfunction. Experimental bed rest in healthy volunteers is an excellent model to explore the detrimental effects of muscle disuse on physiological functions.”
Numerous metabolic processes
Sixteen healthy, young female volunteers from the European Union averaging 32 years of age with a body mass index (BMI) of approximately 21 kg participated in the two-month study in which they were placed in a head-down tilt position (−6°) in bedrest to test the effects of simulated microgravity.
The study showed that women experienced a substantial 7% loss of lean body mass during bed rest, which intensified protein catabolism and development of insulin resistance. This was demonstrated by a diminished capacity of insulin to facilitate glucose utilization.
At the end of the bed rest period, the percent changes of insulin-mediated glucose uptake were significant. It decreased in the conventional diet group from 155 ± 23 % to 84 ± 10 % while did not change significantly in the high protein-BCAA diet group from 126 ± 20 % to 141 ± 27 %.
“In particular, leucine plays multiple roles in numerous metabolic processes, including translation regulation of protein synthesis in skeletal muscle and modulation of the insulin/phosphoinositide 3-kinase (PI3K) signal cascade,” the researchers added. “Moreover, leucine is a primary nitrogen donor for alanine and glutamine production in skeletal muscle and a modulator of the pancreatic β-cell concerning insulin release. Through these mechanisms, leucine and the other BCAAs may directly influence insulin secretion, muscle protein synthesis and insulin action on glucose homeostasis.”
Although the close interactions between the metabolic pathways of carbohydrates and amino acids have been known for years, the impact of high dietary protein on glycemic control is still unclear, the researchers wrote.
“Elevation of plasma amino acids after administration of an amino acid mixture acutely induces insulin resistance in skeletal muscle by inhibiting glucose transport and glucose phosphorylation in humans,” they said. “By contrast, a high protein, low-carbohydrate diet is responsible for postprandial glucose and insulin reduction, blood glucose stabilization and improvement of dyslipidemia for individuals with type 2 diabetes or obesity.”
However, the researchers did note that there are contradictory reports suggesting an inconsistent relationship between BCAAs and glucose metabolism or its disorders, such as type 2 diabetes mellitus and obesity. Recent science shows that plasma BCAAs are elevated in obesity and type 2 diabetes mellitus, conditions characterized by insulin resistance. In addition, several studies have demonstrated that dietary supplementation with BCAAs could be a contributing cause of impaired glucose metabolism.
“In contrast, other studies reported a positive association between dietary BCAA intake and improved glucose metabolism in a large population-based cohort and obese, prediabetic subjects,” they said. “Therefore, these contradictory reports suggest an inconsistent relationship between BCAAs and glucose metabolism or its disorders, such as type 2 diabetes mellitus and obesity.”
Source: Clinical Nutrition
“High-protein diet with excess leucine prevents inactivity-induced insulin resistance in women”
Authors: Alessandro Mangogna et al.