Joan M. G. Senden

Whey protein stimulates postprandial muscle protein accretion more effectively than do casein and casein hydrolysate in older men

BACKGROUND Sarcopenia has been attributed to a diminished muscle protein synthetic response to food intake. Differences in digestion and absorption kinetics of dietary protein, its amino acid composition, or both have been suggested to modulate postprandial muscle protein accretion. OBJECTIVE The objective was to compare protein digestion and absorption kinetics and subsequent postprandial muscle protein accretion after ingestion of whey, casein, and casein hydrolysate in healthy older adults. DESIGN A total of 48 older men aged 74 ± 1 y (mean ± SEM) were randomly assigned to ingest a meal-like amount (20 g) of intrinsically l-[1-(13)C]phenylalanine-labeled whey, casein, or casein hydrolysate. Protein ingestion was combined with continuous intravenous l-[ring-(2)H(5)]phenylalanine infusion to assess in vivo digestion and absorption kinetics of dietary protein. Postprandial mixed muscle protein fractional synthetic rates (FSRs) were calculated from the ingested tracer. RESULTS The peak appearance rate of dietary protein-derived phenylalanine in the circulation was greater with whey and casein hydrolysate than with casein (P < 0.05). FSR values were higher after whey (0.15 ± 0.02%/h) than after casein (0.08 ± 0.01%/h; P < 0.01) and casein hydrolysate (0.10 ± 0.01%/h; P < 0.05) ingestion. A strong positive correlation (r = 0.66, P < 0.01) was observed between peak plasma leucine concentrations and postprandial FSR values. CONCLUSIONS 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 wheys faster digestion and absorption kinetics and higher leucine content. This trial was registered at clinicaltrials.gov as NCT00557388.

Loss of membrane phospholipid asymmetry in platelets and red cells may be associated with calcium-induced shedding of plasma membrane and inhibition of aminophospholipid translocase

Influx of calcium in platelets and red cells produces formation of vesicles shed from the plasma membrane. The time course of the shedding process closely correlates with the ability of both cells to stimulate prothrombinase activity when used as a source of phospholipid in the prothrombinase assay. This reflects increased surface exposure of phosphatidylserine, presumably resulting from a loss in membrane asymmetry. Evidence is presented that the shed vesicles have a random phospholipid distribution, while the remnant cells show a progressive loss of membrane phospholipid asymmetry when more shedding occurs. Removal of intracellular calcium produces a decrease of procoagulant activity of the remnant cells but not of that of the shed vesicles. This is consistent with reactivation of aminophospholipid translocase activity, being first inhibited by intracellular calcium and subsequently reactivated upon calcium removal. Involvement of aminophospholipid translocase is further supported by the observation that reversibility of procoagulant activity is also dependent on metabolic ATP and reduced sulfhydryl groups. The finding that this reversibility process is not apparent in shed vesicles may be ascribed to the absence of translocase or to a lack of ATP. These data support and extend the suggestion made by Sims et al. [1989) J. Biol. Chem. 264, 17049-17057) that membrane fusion, which is required for shedding to occur, produces transient flip-flop sites for membrane phospholipids. Furthermore, the present results indicate that scrambling of membrane phospholipids can only occur provided that aminophospholipid translocase is inactive.

Amino acid absorption and subsequent muscle protein accretion following graded intakes of whey protein in elderly men

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.

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.

BACKGROUND Sarcopenia seems to be attributed to a blunted muscle protein synthetic response to food intake and exercise. This blunted response could be the result of impaired protein digestion and absorption kinetics and lead to lower postprandial plasma amino acid availability. OBJECTIVE The objective was to compare in vivo dietary protein digestion and absorption kinetics and subsequent postprandial muscle protein synthesis rates at rest and after exercise between young and elderly men. DESIGN Young and elderly men consumed a 20-g bolus of intrinsically L-[1-(13)C]phenylalanine-labeled protein at rest or after exercise. Continuous infusions with L-[ring-(2)H(5)]phenylalanine were applied, and blood and muscle samples were collected to assess in vivo protein digestion and absorption kinetics and subsequent postprandial muscle protein synthesis rates. RESULTS Exogenous phenylalanine appearance rates expressed over time did not differ between groups. No differences were observed in plasma phenylalanine availability between the young (51 ± 2%) and elderly (51 ± 1%) men or between the rest (52 ± 1%) and exercise (49 ± 1%) conditions. Muscle protein synthesis rates calculated from the oral tracer were 0.0620 ± 0.0065%/h and 0.0560 ± 0.0039%/h for the rest condition and 0.0719 ± 0.0057%/h and 0.0727 ± 0.0040%/h for the exercise condition in young and elderly men, respectively (age effect: P = 0.62; exercise effect: P < 0.05; interaction of age and exercise: P = 0.52). CONCLUSIONS 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.

Leucine co-ingestion improves post-prandial muscle protein accretion in elderly men

BACKGROUND & AIMS It has been speculated that the amount of leucine in a meal largely determines the post-prandial muscle protein synthetic response to food intake. The present study investigates the impact of leucine co-ingestion on subsequent post-prandial muscle protein accretion following the ingestion of a single bolus of dietary protein in elderly males. METHODS Twenty-four elderly men (74.3±1.0 y) were randomly assigned to ingest 20 g intrinsically L-[1-(13)C]phenylalanine-labeled casein protein with (PRO+LEU) or without (PRO) 2.5 g crystalline leucine. Ingestion of specifically produced intrinsically labeled protein allowed us to create a plasma phenylalanine enrichment pattern similar to the absorption pattern of phenylalanine from the ingested protein and assess the subsequent post-prandial incorporation of L-[1-(13)C] phenylalanine into muscle protein. RESULTS Plasma amino acid concentrations increased rapidly following protein ingestion in both groups, with higher leucine concentrations observed in the PRO+LEU compared with the PRO group (P<0.01). Plasma L-[1-(13)C]phenylalanine enrichments increased rapidly and to a similar extent in both groups following protein ingestion. Muscle protein-bound L-[1-(13)C]phenylalanine enrichments were significantly greater after PRO+LEU when compared with PRO at 2 h (72%; 0.0078±0.0010 vs. 0.0046±0.00100 MPE, respectively; P<0.05) and 6 h (25%; 0.0232±0.0015 vs. 0.0185±0.0010 MPE, respectively; P<0.05) following protein ingestion. The latter translated into a greater muscle protein synthetic rate following PRO+LEU compared with PRO over the entire 6 h post-prandial period (22%; 0.049±0.003 vs. 0.040±0.003% h(-1), respectively; P<0.05). CONCLUSION Leucine co-ingestion with a bolus of pure dietary protein further stimulates post-prandial muscle protein synthesis rates in elderly men.

Protein ingestion before sleep improves postexercise overnight recovery.

INTRODUCTION The role of nutrition in modulating postexercise overnight recovery remains to be elucidated. We assessed the effect of protein ingestion immediately before sleep on digestion and absorption kinetics and protein metabolism during overnight recovery from a single bout of resistance-type exercise. METHODS Sixteen healthy young males performed a single bout of resistance-type exercise in the evening (2000 h) after a full day of dietary standardization. All subjects were provided with appropriate recovery nutrition (20 g of protein, 60 g of CHO) immediately after exercise (2100 h). Thereafter, 30 min before sleep (2330 h), subjects ingested a beverage with (PRO) or without (PLA) 40 g of specifically produced intrinsically [1-C]phenylalanine-labeled casein protein. Continuous intravenous infusions with [ring-H5]phenylalanine and [ring-H2]tyrosine were applied with blood and muscle samples collected to assess protein digestion and absorption kinetics, whole-body protein balance and mixed muscle protein synthesis rates throughout the night (7.5 h). RESULTS During sleep, casein protein was effectively digested and absorbed resulting in a rapid rise in circulating amino acid levels, which were sustained throughout the remainder of the night. Protein ingestion before sleep increased whole-body protein synthesis rates (311 ± 8 vs 246 ± 9 μmol·kg per 7.5 h) and improved net protein balance (61 ± 5 vs -11 ± 6 μmol·kg per 7.5 h) in the PRO vs the PLA experiment (P < 0.01). Mixed muscle protein synthesis rates were ∼22% higher in the PRO vs the PLA experiment, which reached borderline significance (0.059%·h ± 0.005%·h vs 0.048%·h ± 0.004%·h, P = 0.05). CONCLUSIONS This is the first study to show that protein ingested immediately before sleep is effectively digested and absorbed, thereby stimulating muscle protein synthesis and improving whole-body protein balance during postexercise overnight recovery.

Substantial skeletal muscle loss occurs during only 5 days of disuse.

The impact of disuse on the loss of skeletal muscle mass and strength has been well documented. Given that most studies have investigated muscle atrophy after more than 2 weeks of disuse, few data are available on the impact of shorter periods of disuse. We assessed the impact of 5 and 14 days of disuse on skeletal muscle mass, strength and associated intramuscular molecular signalling responses.

Protein Supplementation during Resistance-Type Exercise Training in the Elderly.

INTRODUCTION Resistance training has been well established as an effective treatment strategy to increase skeletal muscle mass and strength in the elderly. We assessed whether dietary protein supplementation can further augment the adaptive response to prolonged resistance-type exercise training in healthy elderly men and women. METHODS Healthy elderly men (n = 31, 70 ± 1 yr) and women (n = 29, 70 ± 1 yr) were randomly assigned to a progressive, 24-wk resistance-type exercise training program with or without additional protein supplementation (15 g·d-1). Muscle hypertrophy was assessed on a whole-body Dual-energy X-ray absorptiometry (DXA), limb (computed tomography), and muscle fiber (biopsy) level. Strength was assessed regularly by 1-repetition maximum (RM) strength testing. Functional capacity was assessed with a sit-to-stand and handgrip test. RESULTS One-RM strength increased by 45% ± 6% versus 40% ± 3% (women) and 41% ± 4% versus 44% ± 3% (men) in the placebo versus protein group, respectively (P < 0.001), with no differences between groups. Leg muscle mass (women, 4% ± 1% vs 3% ± 1%; men, 3% ± 1% vs 3% ± 1%) and quadriceps cross-sectional area (women, 9% ± 1% vs 9% ± 1%; men, 9% ± 1% vs 10% ± 1%) increased similarly in the placebo versus protein groups (P < 0.001). Type II muscle fiber size increased over time in both placebo and protein groups (25% ± 13% vs 30% ± 9% and 23% ± 12% vs 22% ± 10% in the women and men, respectively). Sit-to-stand improved by 18% ± 2% and 19% ± 2% in women and men, respectively (P < 0.001). CONCLUSION Prolonged resistance-type exercise training increases skeletal muscle mass and strength, augments functional capacity, improves glycemia and lipidemia, and reduces blood pressure in healthy elderly men and women. Additional protein supplementation (15 g·d-1) does not further increase muscle mass, strength, and/or functional capacity.

Intragastric protein administration stimulates overnight muscle protein synthesis in elderly men

The loss of skeletal muscle mass with aging has been attributed to an impaired muscle protein synthetic response to food intake. Therefore, nutritional strategies are targeted to modulate postprandial muscle protein accretion in the elderly. The purpose of this study was to assess the impact of protein administration during sleep on in vivo protein digestion and absorption kinetics and subsequent muscle protein synthesis rates in elderly men. Sixteen healthy elderly men were randomly assigned to an experiment during which they were administered a single bolus of intrinsically l-[1-(13)C]phenylalanine-labeled casein protein (PRO) or a placebo (PLA) during sleep. Continuous infusions with l-[ring-(2)H(5)]phenylalanine and l-[ring-(2)H(2)]tyrosine were applied to assess in vivo dietary protein digestion and absorption kinetics and subsequent muscle protein synthesis rates during sleep. We found that exogenous phenylalanine appearance rates increased following protein administration. The latter stimulated protein synthesis, resulting in a more positive overnight whole body protein balance (0.30 ± 0.1 vs. 11.8 ± 1.0 μmol phenylalanine·kg(-1)·h(-1) in PLA and PRO, respectively; P < 0.05). In agreement, overnight muscle protein fractional synthesis rates were much greater in the PRO experiment (0.045 ± 0.002 vs. 0.029 ± 0.002%/h, respectively; P < 0.05) and showed abundant incorporation of the amino acids ingested via the intrinsically labeled protein (0.058 ± 0.006%/h). This is the first study to show that dietary protein administration during sleep is followed by normal digestion and absorption kinetics, thereby stimulating overnight muscle protein synthesis. Dietary protein administration during sleep stimulates muscle protein synthesis and improves overnight whole body protein balance. These findings may provide a basis for novel interventional strategies to attenuate muscle mass loss.

Minced beef is more rapidly digested and absorbed than beef steak, resulting in greater postprandial protein retention in older men

BACKGROUND Older individuals generally experience a reduced food-chewing efficiency. As a consequence, food texture may represent an important factor that modulates dietary protein digestion and absorption kinetics and the subsequent postprandial protein balance. OBJECTIVE We assessed the effect of meat texture on the dietary protein digestion rate, amino acid availability, and subsequent postprandial protein balance in vivo in older men. DESIGN Ten older men (mean ± SEM age: 74 ± 2 y) were randomly assigned to a crossover experiment that involved 2 treatments in which they consumed 135 g of specifically produced intrinsically L-[1-(13)C]phenylalanine-labeled beef, which was provided as beef steak or minced beef. Meat consumption was combined with continuous intravenous L-[ring-(2)H5]phenylalanine and L-[ring-(2)H2]tyrosine infusion to assess beef protein digestion and absorption kinetics as well as whole-body protein balance and skeletal muscle protein synthesis rates. RESULTS Meat protein-derived phenylalanine appeared more rapidly in the circulation after minced beef than after beef steak consumption (P < 0.05). Also, its availability in the circulation during the 6-h postprandial period was greater after minced beef than after beef steak consumption (61 ± 3% compared with 49 ± 3%, respectively; P < 0.01). The whole-body protein balance was more positive after minced beef than after beef steak consumption (29 ± 2 compared with 19 ± 3 μmol phenylalanine/kg, respectively; P < 0.01). Skeletal muscle protein synthesis rates did not differ between treatments when assessed over a 6-h postprandial period. CONCLUSIONS Minced beef is more rapidly digested and absorbed than beef steak, which results in increased amino acid availability and greater postprandial protein retention. However, this does not result in greater postprandial muscle protein synthesis rates. This trial was registered at clinicaltrials.gov as NCT01145131.