Arie K. Kies

Ingestion of a protein hydrolysate is accompanied by an accelerated in vivo digestion and absorption rate when compared with its intact protein

BACKGROUND It has been suggested that a protein hydrolysate, as opposed to its intact protein, is more easily digested and absorbed from the gut, which results in greater plasma amino acid availability and a greater muscle protein synthetic response. OBJECTIVE We aimed to compare dietary protein digestion and absorption kinetics and the subsequent muscle protein synthetic response to the ingestion of a single bolus of protein hydrolysate compared with its intact protein in vivo in humans. DESIGN Ten elderly men (mean +/- SEM age: 64 +/- 1 y) were randomly assigned to a crossover experiment that involved 2 treatments in which the subjects consumed a 35-g bolus of specifically produced L-[1-(13)C]phenylalanine-labeled intact casein (CAS) or hydrolyzed casein (CASH). Blood and muscle-tissue samples were collected to assess the appearance rate of dietary protein-derived phenylalanine in the circulation and subsequent muscle protein fractional synthetic rate over a 6-h postprandial period. RESULTS The mean (+/-SEM) exogenous phenylalanine appearance rate was 27 +/- 6% higher after ingestion of CASH than after ingestion of CAS (P < 0.001). Splanchnic extraction was significantly lower in CASH compared with CAS treatment (P < 0.01). Plasma amino acid concentrations increased to a greater extent (25-50%) after the ingestion of CASH than after the ingestion of CAS (P < 0.01). Muscle protein synthesis rates averaged 0.054 +/- 0.004% and 0.068 +/- 0.006%/h in the CAS and CASH treatments, respectively (P = 0.10). CONCLUSIONS Ingestion of a protein hydrolysate, as opposed to its intact protein, accelerates protein digestion and absorption from the gut, augments postprandial amino acid availability, and tends to increase the incorporation rate of dietary amino acids into skeletal muscle protein.

Dietary Protein Digestion and Absorption Rates and the Subsequent Postprandial Muscle Protein Synthetic Response Do Not Differ between Young and Elderly Men

Impaired digestion and/or absorption of dietary protein lowers postprandial plasma amino acid availability and, as such, could reduce the postprandial muscle protein synthetic response in the elderly. We aimed to compare in vivo dietary protein digestion and absorption and the subsequent postprandial muscle protein synthetic response between young and elderly men. Ten elderly (64 +/- 1 y) and 10 young (23 +/- 1 y) healthy males consumed a single bolus of 35 g specifically produced, intrinsically l-[1-(13)C]phenylalanine-labeled micellar casein (CAS) protein. Furthermore, primed continuous infusions with l-[ring-(2)H(5)]phenylalanine, l-[1-(13)C]leucine, and l-[ring-(2)H(2)]tyrosine were applied and blood and muscle tissue samples were collected to assess the appearance rate of dietary protein-derived phenylalanine in the circulation and the subsequent muscle protein fractional synthetic rate over a 6-h postprandial period. Protein ingestion resulted in a rapid increase in exogenous phenylalanine appearance in both the young and elderly men. Total exogenous phenylalanine appearance rates (expressed as area under the curve) were 39 +/- 3 mumol.6 h.kg(-1) in the young men and 38 +/- 2 mumol.6 h.kg(-1) in the elderly men (P = 0.73). In accordance, splanchnic amino acid extraction did not differ between young (72 +/- 2%) and elderly (73 +/- 1%) volunteers (P = 0.74). Muscle protein synthesis rates, calculated from the oral tracer, were 0.063 +/- 0.006 and 0.054 +/- 0.004%/h in the young and elderly men, respectively, and did not differ between groups (P = 0.27). We conclude that protein digestion and absorption kinetics and the subsequent muscle protein synthetic response following the ingestion of a large bolus of intact CAS are not substantially impaired in healthy, elderly men.

Coingestion of Carbohydrate and Protein Hydrolysate Stimulates Muscle Protein Synthesis during Exercise in Young Men, with No Further Increase during Subsequent Overnight Recovery

We investigated the effect of carbohydrate and protein hydrolysate ingestion on whole-body and muscle protein synthesis during a combined endurance and resistance exercise session and subsequent overnight recovery. Twenty healthy men were studied in the evening after consuming a standardized diet throughout the day. Subjects participated in a 2-h exercise session during which beverages containing both carbohydrate (0.15 g x kg(-1) x h(-1)) and a protein hydrolysate (0.15 g x kg(-1) x h(-1)) (C+P, n = 10) or water only (W, n = 10) were ingested. Participants consumed 2 additional beverages during early recovery and remained overnight at the hospital. Continuous i.v. infusions with L-[ring-(13)C(6)]-phenylalanine and L-[ring-(2)H(2)]-tyrosine were applied and blood and muscle samples were collected to assess whole-body and muscle protein synthesis rates. During exercise, whole-body and muscle protein synthesis rates increased by 29 and 48% with protein and carbohydrate coingestion (P < 0.05). Fractional synthetic rates during exercise were 0.083 +/- 0.011%/h in the C+P group and 0.056 +/- 0.003%/h in the W group, (P < 0.05). During subsequent overnight recovery, whole-body protein synthesis was 19% greater in the C+P group than in the W group (P < 0.05). However, mean muscle protein synthesis rates during 9 h of overnight recovery did not differ between groups and were 0.056 +/- 0.004%/h in the C+P group and 0.057 +/- 0.004%/h in the W group (P = 0.89). We conclude that, even in a fed state, protein and carbohydrate supplementation stimulates muscle protein synthesis during exercise. Ingestion of protein with carbohydrate during and immediately after exercise improves whole-body protein synthesis but does not further augment muscle protein synthesis rates during 9 h of subsequent overnight recovery.

Protein coingestion stimulates muscle protein synthesis during resistance-type exercise

In contrast to the effect of nutritional intervention on postexercise muscle protein synthesis, little is known about the potential to modulate protein synthesis during exercise. This study investigates the effect of protein coingestion with carbohydrate on muscle protein synthesis during resistance-type exercise. Ten healthy males were studied in the evening after they consumed a standardized diet throughout the day. Subjects participated in two experiments in which they ingested either carbohydrate or carbohydrate with protein during a 2-h resistance exercise session. Subjects received a bolus of test drink before and every 15 min during exercise, providing 0.15 g x kg(-1) x h(-1) carbohydrate with (CHO + PRO) or without (CHO) 0.15 g x kg(-1) x h(-1) protein hydrolysate. Continuous intravenous infusions with l-[ring-(13)C(6)]phenylalanine and l-[ring-(2)H(2)]tyrosine were applied, and blood and muscle biopsies were collected to assess whole body and muscle protein synthesis rates during exercise. Protein coingestion lowered whole body protein breakdown rates by 8.4 +/- 3.6% (P = 0.066), compared with the ingestion of carbohydrate only, and augmented protein oxidation and synthesis rates by 77 +/- 17 and 33 +/- 3%, respectively (P < 0.01). As a consequence, whole body net protein balance was negative in CHO, whereas a positive net balance was achieved after the CHO + PRO treatment (-4.4 +/- 0.3 vs. 16.3 +/- 0.4 micromol phenylalanine x kg(-1) x h(-1), respectively; P < 0.01). In accordance, mixed muscle protein fractional synthetic rate was 49 +/- 22% higher after protein coingestion (0.088 +/- 0.012 and 0.060 +/- 0.004%/h in CHO + PRO vs. CHO treatment, respectively; P < 0.05). We conclude that, even in a fed state, protein coingestion stimulates whole body and muscle protein synthesis rates during resistance-type exercise.

The production of intrinsically labeled milk protein provides a functional tool for human nutrition research

Oral or intravenous administration of labeled, free amino acids does not allow the direct assessment of protein digestion and absorption kinetics following dietary protein intake. Consequently, dietary protein sources with labeled amino acids incorporated within the protein are required. The aim of this study was to produce milk proteins intrinsically labeled with l-[1-(13)C]phenylalanine that would allow the assessment of protein digestion and absorption kinetics and the subsequent muscle protein synthetic response to dietary protein intake in vivo in humans. Two Holstein cows (body weight of 726 +/- 38 kg) were continuously infused with l-[1-(13)C]phenylalanine at 402 micromol/min for 44 to 48 h, during and after which plasma samples and milk were collected. After milk protein separation, casein was used in a subsequent human proof-of-principle experiment. Two healthy males (aged 61 +/- 1 yr; body mass index of 22.4 +/- 0.1 kg/m(2)) ingested 35 g of casein highly enriched with [1-(13)C] phenylalanine. Plasma samples were collected at regular intervals, and skeletal muscle biopsies were collected before and 6 h after casein ingestion. In the initial experiment, a total of 5.83 kg of l-[1-(13)C]phenylalanine-enriched milk protein (casein enrichment was 29.4 molar percent excess) was collected during stable isotope infusion in the cows. In the proof-of-principle study, ingestion of 35 g of intrinsically labeled casein resulted in peak plasma l-[1-(13)C]phenylalanine enrichments within 90 min after protein ingestion (9.75 +/- 1.47 molar percent excess). Skeletal muscle protein synthesis rates calculated over the entire 6-h period averaged 0.058 +/- 0.012%/h. The production of intrinsically labeled milk protein is feasible and provides dietary protein that can be used to investigate protein digestion and absorption and the subsequent muscle protein synthetic response in vivo in humans.

Pharmacokinetics of proline-rich tripeptides in the pig

Tripeptides may possess bioactive properties. For instance, blood pressure lowering is attributed to the proline-rich tripeptides Ile-Pro-Pro (IPP), Leu-Pro-Pro (LPP), and Val-Pro-Pro (VPP). However, little is known about their absorption, distribution, and elimination characteristics. The aim of this study was to characterize the pharmacokinetic behavior of IPP, LPP, and VPP in a conscious pig model. Synthetic IPP, LPP, and VPP were administered intravenously or intragastrically (4.0 mg kg(-1) BW in saline) to 10 piglets (approximately 25 kg body weight) in the postabsorptive state. After intravenous dosing, the elimination half-life for IPP was significantly higher (P<0.001) than for LPP and VPP (2.5+/-0.1, 1.9+/-0.1, and 2.0+/-0.1 min, respectively). After intragastric dosing, however, the elimination half-lives were not significantly different between the peptides (9+/-1, 15+/-4, and 12+/-6 min, respectively). Maximum plasma concentrations were about 10 nmol l(-1) for the three tripeptides. The fraction dose absorbed was 0.077+/-0.010, 0.059+/-0.009, and 0.073+/-0.015%, for IPP, LPP, and VPP, respectively. Proline-rich tripeptides reach the blood circulation intact, with an absolute bioavailability of about 0.1% when administered via a saline solution. Because half-lives of absorption and elimination were maximally about 5 and 15 min, respectively, this suggests that under these conditions a bioactive effect of these tripeptides would be rather acute.

Protein Ingestion before Sleep Increases Muscle Mass and Strength Gains during Prolonged Resistance-Type Exercise Training in Healthy Young Men

BACKGROUND It has been demonstrated that protein ingestion before sleep increases muscle protein synthesis rates during overnight recovery from an exercise bout. However, it remains to be established whether dietary protein ingestion before sleep can effectively augment the muscle adaptive response to resistance-type exercise training. OBJECTIVE Here we assessed the impact of dietary protein supplementation before sleep on muscle mass and strength gains during resistance-type exercise training. METHODS Forty-four young men (22 ± 1 y) were randomly assigned to a progressive, 12-wk resistance exercise training program. One group consumed a protein supplement containing 27.5 g of protein, 15 g of carbohydrate, and 0.1 g of fat every night before sleep. The other group received a noncaloric placebo. Muscle hypertrophy was assessed on a whole-body (dual-energy X-ray absorptiometry), limb (computed tomography scan), and muscle fiber (muscle biopsy specimen) level before and after exercise training. Strength was assessed regularly by 1-repetition maximum strength testing. RESULTS Muscle strength increased after resistance exercise training to a significantly greater extent in the protein-supplemented (PRO) group than in the placebo-supplemented (PLA) group (+164 ± 11 kg and +130 ± 9 kg, respectively; P < 0.001). In addition, quadriceps muscle cross-sectional area increased in both groups over time (P < 0.001), with a greater increase in the PRO group than in the PLA group (+8.4 ± 1.1 cm(2) vs. +4.8 ± 0.8 cm(2), respectively; P < 0.05). Both type I and type II muscle fiber size increased after exercise training (P < 0.001), with a greater increase in type II muscle fiber size in the PRO group (+2319 ± 368 μm(2)) than in the PLA group (+1017 ± 353 μm(2); P < 0.05). CONCLUSION Protein ingestion before sleep represents an effective dietary strategy to augment muscle mass and strength gains during resistance exercise training in young men. This trial was registered at clinicaltrials.gov as NCT02222415.

High dietary protein restores overreaching induced impairments in leukocyte trafficking and reduces the incidence of upper respiratory tract infection in elite cyclists

The present study examined whether a high protein diet prevents the impaired leukocyte redistribution in response to acute exercise caused by a large volume of high-intensity exercise training. Eight cyclists (VO2max: 64.2±6.5mLkg(-1)min(-1)) undertook two separate weeks of high-intensity training while consuming either a high protein diet (3gkg(-1)proteinBM(-1)day(-1)) or an energy and carbohydrate-matched control diet (1.5gkg(-1)proteinBM(-1)day(-1)). High-intensity training weeks were preceded by a week of normal-intensity training under the control diet. Leukocyte and lymphocyte sub-population responses to acute exercise were determined at the end of each training week. Self-reported symptoms of upper-respiratory tract infections (URTI) were monitored daily by questionnaire. Undertaking high-intensity training with a high protein diet restored leukocyte kinetics to similar levels observed during normal-intensity training: CD8(+) TL mobilization (normal-intensity: 29,319±13,130cells/μL×∼165min vs. high-intensity with protein: 26,031±17,474cells/μL×∼165min, P>0.05), CD8(+) TL egress (normal-intensity: 624±264cells/μL vs. high-intensity with protein: 597±478cells/μL, P>0.05). This pattern was driven by effector-memory populations mobilizing (normal-intensity: 6,145±6,227cells/μL×∼165min vs. high-intensity with protein: 6,783±8,203cells/μL×∼165min, P>0.05) and extravastating from blood (normal-intensity: 147±129cells/μL vs. high-intensity with protein: 165±192cells/μL, P>0.05). High-intensity training while consuming a high protein diet was associated with fewer symptoms of URTI compared to performing high-intensity training with a normal diet (P<0.05). To conclude, a high protein diet might reduce the incidence of URTI in athletes potentially mediated by preventing training-induced impairments in immune-surveillance.

Changes in myonuclear domain size do not precede muscle hypertrophy during prolonged resistance-type exercise training

Muscle fibre hypertrophy is accompanied by an increase in myonuclear number, an increase in myonuclear domain size or both. It has been suggested that increases in myonuclear domain size precede myonuclear accretion and subsequent muscle fibre hypertrophy during prolonged exercise training. In this study, we assessed the changes in muscle fibre size, myonuclear and satellite cell content throughout 12 weeks of resistance‐type exercise training in young men.

Enhanced Lacto-Tri-Peptide Bio-Availability by Co-Ingestion of Macronutrients

Some food-derived peptides possess bioactive properties, and may affect health positively. For example, the C-terminal lacto-tri-peptides Ile-Pro-Pro (IPP), Leu-Pro-Pro (LPP) and Val-Pro-Pro (VPP) (together named here XPP) are described to lower blood pressure. The bioactivity depends on their availability at the site of action. Quantitative trans-organ availability/kinetic measurements will provide more insight in C-terminal tri-peptides behavior in the body. We hypothesize that the composition of the meal will modify their systemic availability. We studied trans-organ XPP fluxes in catheterized pigs (25 kg; n=10) to determine systemic and portal availability, as well as renal and hepatic uptake of a water-based single dose of synthetic XPP and a XPP containing protein matrix (casein hydrolyte, CasH). In a second experiment (n=10), we compared the CasH-containing protein matrix with a CasH-containing meal matrix and the modifying effects of macronutrients in a meal on the availability (high carbohydrates, low quality protein, high fat, and fiber). Portal availability of synthetic XPP was 0.08 ± 0.01% of intake and increased when a protein matrix was present (respectively 3.1, 1.8 and 83 times for IPP, LPP and VPP). Difference between individual XPP was probably due to release from longer peptides. CasH prolonged portal bioavailability with 18 min (absorption half-life, synthetic XPP: 15 ± 2 min, CasH: 33 ± 3 min, p<0.0001) and increased systemic elimination with 20 min (synthetic XPP: 12 ± 2 min; CasH: 32 ± 3 min, p<0.0001). Subsequent renal and hepatic uptake is about 75% of the portal release. A meal containing CasH, increased portal 1.8 and systemic bioavailability 1.2 times. Low protein quality and fiber increased XPP systemic bioavailability further (respectively 1.5 and 1.4 times). We conclude that the amount and quality of the protein, and the presence of fiber in a meal, are the main factors that increase the systemic bioavailability of food-derived XPP.