Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men. This effect is attributed to a combination of whey's faster digestion and absorption kinetics and higher leucine content. This trial was registered at clinicaltrials.gov as NCT00557388.

An eight-electrode conductance catheter previously developed by us and used to determine stroke volume in dogs was applied in human beings and dogs to measure absolute left ventricular volume quantitatively. For calibration we developed the formula V(t) = (l/a)(L2/Yb)G(t) -

The postprandial rise in essential amino acid (EAA) concentrations modulates the increase in muscle protein synthesis rates after protein ingestion. The EAA content and AA composition of the dietary protein source contribute to the differential muscle protein synthetic response to the ingestion of different proteins. Lower EAA contents and specific lack of sufficient leucine, lysine, and/or methionine may be responsible for the lower anabolic capacity of plant-based compared with animal-based proteins. We compared EAA contents and AA composition of a large selection of plant-based protein sources with animal-based proteins and human skeletal muscle protein. AA composition of oat, lupin, wheat, hemp, microalgae, soy, brown rice, pea, corn, potato, milk, whey, caseinate, casein, egg, and human skeletal muscle protein were assessed using UPLC–MS/MS. EAA contents of plant-based protein isolates such as oat (21%), lupin (21%), and wheat (22%) were lower than animal-based proteins (whey 43%, milk 39%, casein 34%, and egg 32%) and muscle protein (38%). AA profiles largely differed among plant-based proteins with leucine contents ranging from 5.1% for hemp to 13.5% for corn protein, compared to 9.0% for milk, 7.0% for egg, and 7.6% for muscle protein. Methionine and lysine were typically lower in plant-based proteins (1.0 ± 0.3 and 3.6 ± 0.6%) compared with animal-based proteins (2.5 ± 0.1 and 7.0 ± 0.6%) and muscle protein (2.0 and 7.8%, respectively). In conclusion, there are large differences in EAA contents and AA composition between various plant-based protein isolates. Combinations of various plant-based protein isolates or blends of animal and plant-based proteins can provide protein characteristics that closely reflect the typical characteristics of animal-based proteins.

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.

We conclude that even short periods of muscle disuse can cause substantial loss of skeletal muscle mass and strength and are accompanied by an early catabolic molecular signalling response.

Whey protein ingestion has been shown to effectively stimulate postprandial muscle protein accretion in older adults. However, the impact of the amount of whey protein ingested on protein digestion and absorption kinetics, whole body protein balance, and postprandial muscle protein accretion remains to be established. We aimed to fill this gap by including 33 healthy, older men (73 ± 2 yr) who were randomly assigned to ingest 10, 20, or 35 g of intrinsically l-[1-13C]phenylalanine-labeled whey protein ( n = 11/treatment). Ingestion of labeled whey protein was combined with continuous intravenous l-[ ring-2H5]phenylalanine and l-[ ring-2H2]tyrosine infusion to assess the metabolic fate of whey protein-derived amino acids. Dietary protein digestion and absorption rapidly increased following ingestion of 10, 20, and 35 g whey protein, with the lowest and highest (peak) values observed following 10 and 35 g, respectively ( P < 0.05). Whole body net protein balance was positive in all groups (19 ± 1, 37 ± 2, and 58 ± 2 μmol/kg), with the lowest and highest values observed following ingestion of 10 and 35 g, respectively ( P < 0.05). Postprandial muscle protein accretion, assessed by l-[1-13C]phenylalanine incorporation in muscle protein, was higher following ingestion of 35 g when compared with 10 ( P < 0.01) or 20 ( P < 0.05) g. We conclude that ingestion of 35 g whey protein results in greater amino acid absorption and subsequent stimulation of de novo muscle protein synthesis compared with the ingestion of 10 or 20 g whey protein in healthy, older men.

A B S T R A C TThe aim of the present study was to establish whether gastro-intestinal (GI) complaints observed during and after ultra-endurance exercise are related to gut ischaemia-associated leakage of endotoxins [lipopolysaccharide (LPS)] into the circulation and associated cytokine production. Therefore we collected blood samples from 29 athletes before, immediately after, and 1, 2 and 16 h after a long-distance triathlon for measurement of LPS, tumour necrosis factor-α and interleukin-6 (IL-6). As the cytokine response would trigger an acute-phase response, characteristic variables of these responses were also measured, along with creatine kinase (CK) to obtain an indicator of muscle damage. There was a high incidence (93 % of all participants) of GI symptoms ; 45 % reported severe complaints and 7 % of the participants abandoned the race because of severe GI distress. Mild endotoxaemia (5-15 pg/ml) was evident in 68 % of the athletes immediately after the race, as also indicated by a reduction in IgG anti-LPS levels. In addition, we observed production of IL-6 (27-fold increase immediately after the race), leading to an acutephase response (20-fold increase in C-reactive protein and 12 % decrease in pre-albumin 16 h after the race). The extent of endotoxaemia was not correlated with the GI complaints or the IL-6 response, but did show a correlation with the elevation in C-reactive protein (r s 0.389 ; P l 0.037). Creatine kinase levels were increased significantly immediately post-race, and increased further in the follow-up period. Creatine kinase levels did not correlate with those of either IL-6 or C-reactive protein. It is therefore concluded that LPS does enter the circulation after ultra-endurance exercise and may, together with muscle damage, be responsible for the increased cytokine response and hence GI complaints in these athletes.

The present study was designed to determine postexercise muscle protein synthesis and whole body protein balance following the combined ingestion of carbohydrate with or without protein and/or free leucine. Eight male subjects were randomly assigned to three trials in which they consumed drinks containing either carbohydrate (CHO), carbohydrate and protein (CHO+PRO), or carbohydrate, protein, and free leucine (CHO+PRO+Leu) following 45 min of resistance exercise. A primed, continuous infusion of L-[ring-13C6]phenylalanine was applied, with blood samples and muscle biopsies collected to assess fractional synthetic rate (FSR) in the vastus lateralis muscle as well as whole body protein turnover during 6 h of postexercise recovery. Plasma insulin response was higher in the CHO+PRO+Leu compared with the CHO and CHO+PRO trials (+240 +/- 19% and +77 +/- 11%, respectively, P < 0.05). Whole body protein breakdown rates were lower, and whole body protein synthesis rates were higher, in the CHO+PRO and CHO+PRO+Leu trials compared with the CHO trial (P < 0.05). Addition of leucine in the CHO+PRO+Leu trial resulted in a lower protein oxidation rate compared with the CHO+PRO trial. Protein balance was negative during recovery in the CHO trial but positive in the CHO+PRO and CHO+PRO+Leu trials. In the CHO+PRO+Leu trial, whole body net protein balance was significantly greater compared with values observed in the CHO+PRO and CHO trials (P < 0.05). Mixed muscle FSR, measured over a 6-h period of postexercise recovery, was significantly greater in the CHO+PRO+Leu trial compared with the CHO trial (0.095 +/- 0.006 vs. 0.061 +/- 0.008%/h, respectively, P < 0.05), with intermediate values observed in the CHO+PRO trial (0.0820 +/- 0.0104%/h). We conclude that coingestion of protein and leucine stimulates muscle protein synthesis and optimizes whole body protein balance compared with the intake of carbohydrate only.