Acute lysine supplementation does not improve hepatic or peripheral insulin sensitivity in older, overweight individuals.

CONTEXT: Lysine supplementation may have a positive influence on the regulation of glucose metabolism but it has not been tested in the geriatric population. OBJECTIVE: We evaluated the impact of acute lysine supplementation using three randomized experimental scenarios: 1) oral glucose alone (control), 2) oral glucose and low-dose lysine (2 grams), and oral glucose and high dose lysine (5 grams) lysine in 7 older (66 ± 1 years/age), overweight/obese (BMI = 28 ± 2 kg/m(2)) individuals. METHODS: We utilized a dual tracer technique (i.e., [6,6-(2)H2] glucose primed constant infusion and 1-[(13)C] glucose oral ingestion) during an oral glucose tolerance test (OGTT) to examine differences in hepatic and peripheral insulin sensitivity under all three scenarios. RESULTS: Post-absorptive plasma glucose and insulin concentrations were not different between the three trials. Similarly, the response of glucose and insulin concentrations during the oral glucose tolerance tests (OGTT) was similar in the three trials. The results of the Matsuda index (ISI/M) were also not different between the three trials. As an index of hepatic insulin sensitivity, there were no significant differences in the endogenous glucose rate of appearance (glucose Ra) for control, 2 g lysine and 5 g lysine (1.2 ± 0.1, 1.1 ± 0.1, 1.3 ± 0.1 mg•kg(-1)•min(-1)), respectively. With respect to peripheral insulin sensitivity, there were no significant differences in the glucose rate of disappearance (glucose Rd) for control, 2 g lysine and 5 g lysine (4.2 ± 0.1, 4.3 ± 0.2, and 4.5 ± 0.4 mg•kg(-1)•min(-1)), respectively. CONCLUSIONS: Previous studies in younger participants have suggested that lysine may have a beneficial effect on glucose metabolism. However, acute lysine supplementation in the older population does not facilitate beneficial changes in glucose Ra or glucose Rd.

EAA supplementation to increase nitrogen intake improves muscle function during bed rest in the elderly.

BACKGROUND & AIMS: Older individuals are more likely to experience extended hospitalization and become protein malnourished during hospitalization. The concomitant compulsory inactivity results in functional decline. Increasing protein intake in hospitalized patients improves nitrogen balance, but effects on function are unknown. In the present study, we examined the effects of increasing protein intake by essential amino acid (EAA) supplementation in older individuals subjected to 10 d bed rest on LBM and muscle function. METHODS: Subjects were given a placebo (n=12, 68+/-5 (SD) yrs, 83+/-19 kg) or 15 g of EAA (n=10, 71+/-6, 72+/-8 kg) 3 times per day throughout 10d of bed rest. LBM, muscle protein synthesis, and muscle function were determined before and after bed rest. Due to an imbalance in randomized gender distribution between groups, gender and beginning functional and LBM measures were utilized for analyses by repeated measures analysis of covariance (RMANCOVA). RESULTS: Analyses revealed the potential for the preservation of functional outcomes with EAA supplementation. CONCLUSIONS: Increasing protein intake above the RDA may preserve muscle function in the elderly during compulsory inactivity. EAA supplementation is potentially an efficient method of increasing protein intake without affecting satiety.

Human soleus and vastus lateralis muscle protein metabolism with an amino acid infusion.

The calf muscles, compared with the thigh, are less responsive to resistance exercise in ambulatory and bed-rested individuals, apparently due to muscle-specific differences in protein metabolism. We chose to evaluate the efficacy of using amino acids to elevate protein synthesis in the soleus, because amino acids have been shown to have a potent anabolic effect in the vastus lateralis. Mixed muscle protein synthesis in the soleus and vastus lateralis was measured before and after infusion of mixed amino acids in 10 individuals (28 +/- 1 yr). Phosphorylation of ribosomal protein p70 S6 kinase (p70S6K; Thr389) and eukaryotic initiation factor 4E-binding protein-1 (4E-BP1; Thr37/46) was also evaluated at rest and after 3 h of amino acid infusion. Basal protein synthesis was similar (P = 0.126), and amino acids stimulated protein synthesis to a similar extent (P = 0.004) in the vastus lateralis (0.043 +/- 0.011%/h) and soleus (0.032 +/- 0.017%/h). Phosphorylation of p70S6K (P = 0.443) and 4E-BP1 (P = 0.192) was not increased in either muscle; however, the soleus contained more total (P = 0.002) and phosphorylated (P = 0.013) 4E-BP1 than the vastus lateralis. These data support the need for further study of amino acid supplementation as a means to compensate for the reduced effectiveness of calf resistance exercise in ambulatory individuals and those exposed to extended periods of unloading. The greater 4E-BP1 in the soleus suggests that there is a muscle-specific distribution of general translational initiation machinery in human skeletal muscle.