Exercising before protein intake allows for greater use of dietary protein–derived amino acids for de novo muscle protein synthesis in both young and elderly men

Abstract

Dietary protein digestion and absorption kinetics are not impaired after exercise or at an older age. Exercising before protein intake allows for a greater use of dietary protein-derived amino acids for de novo muscle protein synthesis in both young and elderly men. This trial was registered at clinicaltrials.gov as NCT00557388.

The muscle protein synthetic response to the combined ingestion of protein and carbohydrate is not impaired in healthy older men

“…However, data on this topic are equivocal, and there are various reasons to suggest that anabolic resistance is not a characteristic of aging per se (Burd et al 2012a, b). Data from our lab Pennings et al 2011b) as well others (Paddon-Jones et al 2004;Symons et al 2007Symons et al , 2011) have failed to detect any age-related differences in the post-prandial muscle protein synthetic response to dietary protein ingestion. A classic work by Volpi et al (2000) indicates that the proposed age-related blunting of the post-prandial muscle protein synthetic response to food intake may be more pronounced under conditions where both amino acids and carbohydrates are administered.…”

“…Clearly, age does not necessarily impair the capacity to direct ingested protein towards muscle protein synthesis. Using this approach, we extend on a previous work from our lab Pennings et al 2011b) as well as from other labs (Paddon-Jones et al 2004;Symons et al 2007Symons et al , 2011Chevalier et al 2011), further supporting the concept that anabolic resistance is not a characteristic of aging per se (Burd et al 2012a). We speculate that impairments in the post-prandial muscle protein synthetic response are likely more evident in more compromised, frail, and sedentary elderly populations, especially during short periods of hospitalization, bed rest, and/or immobilization Tieland et al 2012;Burd et al 2012a), as opposed to the healthy, independently living elderly included in the present study.…”

“…13 C]phenylalanine-labeled protein, specifically produced by the infusion of large amounts of tracer in a lactating Holstein cow (Pennings et al 2011c;van Loon et al 2009b), we are able to detect the appearance of dietary protein-derived phenylalanine in the circulation (Fig.3) and assess its subsequent incorporation in skeletal muscle protein Koopman et al 2009b;Pennings et al 2011a;Pennings et al 2011b;. Two hours after ingestion of the protein, skeletal muscle protein already showed a substantial increase in [1-13 C]phenylalanine enrichment (0.0071±0.0016 and 0.0072±0.0013 MPE in the young and older group, respectively; P=0.97).…”

“…In the early post-prandial period, plasma amino acid levels and [1-13 C]phenylalanine enrichments tended to be higher in the young versus the older group. This apparent delay in plasma amino acid concentrations and enrichments can be accounted for by either a delayed digestion and/or absorption rate (Boirie et al 1997;Volpi et al 1999;Koopman et al 2009b;Pennings et al 2011b), and/or a greater amino acid uptake secondary to the compensatory hyperinsulinemia (Hatzakorzian et al 2011) (Fig.1b), and/or an attenuated inhibition of the post-prandial reduction in protein breakdown (Wilkes et al 2009). …”

“…This blunted post-prandial muscle protein synthetic response is now generally thought to represent a key factor responsible for the age-related decline in skeletal muscle mass. However, there is an ongoing debate about the existence and extent of anabolic resistance in a healthy elderly population (Burd et al 2012a, b), since various studies have failed to confirm the presence of anabolic resistance in a physiological setting where post-prandial muscle protein synthesis rates were assessed following ingestion of a single meal-like bolus of protein Paddon-Jones et al 2004;Pennings et al 2011b;Symons et al 2007Symons et al , 2011.…”