Type II Muscle Fiber Capillarization Is an Important Determinant of Post-Exercise Microvascular Perfusion in Older Adults.

INTRODUCTION: Microvascular perfusion is essential for post-exercise skeletal muscle recovery to ensure adequate delivery of nutrients and growth factors. This study assessed the relationship between various indices of muscle fiber capillarization and microvascular perfusion assessed by contrast-enhanced ultrasound (CEUS) at rest and during recovery from a bout of resistance exercise in older adults. METHODS: Sixteen older adults (72 ± 6 y, 5/11 male/female) participated in an experimental test day during which a muscle biopsy was collected from the vastus lateralis and microvascular perfusion was determined by CEUS at rest and at 10 and 40 min following a bout of resistance exercise. Immunohistochemistry was performed on muscle tissue samples to determine various indices of both mixed and fiber-type-specific muscle fiber capillarization. RESULTS: Microvascular blood volume at t = 10 min was higher compared with rest and t = 40 min (27.2 ± 4.7 vs. 3.9 ± 4.0 and 7.0 ± 4.9 AU, respectively, both p < 0.001). Microvascular blood volume at t = 40 min was higher compared with rest (p < 0.001). No associations were observed between different indices of mixed muscle fiber capillarization and microvascular blood volume at rest and following exercise. A moderate (r = 0.59, p < 0.05) and strong (r = 0.81, p < 0.001) correlation was observed between type II muscle fiber capillary-to-fiber ratio and the microvascular blood volume increase from rest to t = 10 and t = 40 min, respectively. In addition, type II muscle fiber capillary contacts and capillary-to-fiber perimeter exchange index were strongly correlated with the microvascular blood volume increase from rest to t = 40 min (r = 0.66, p < 0.01 and r = 0.64, p < 0.01, respectively). CONCLUSION: Resistance exercise strongly increases microvascular blood volume for at least 40 min after exercise cessation in older adults. This resistance exercise-induced increase in microvascular blood volume is strongly associated with type II muscle fiber capillarization in older adults.

The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans.

The belief that the anabolic response to feeding during postexercise recovery is transient and has an upper limit and that excess amino acids are being oxidized lacks scientific proof. Using a comprehensive quadruple isotope tracer feeding-infusion approach, we show that the ingestion of 100 g protein results in a greater and more prolonged (>12 h) anabolic response when compared to the ingestion of 25 g protein. We demonstrate a dose-response increase in dietary-protein-derived plasma amino acid availability and subsequent incorporation into muscle protein. Ingestion of a large bolus of protein further increases whole-body protein net balance, mixed-muscle, myofibrillar, muscle connective, and plasma protein synthesis rates. Protein ingestion has a negligible impact on whole-body protein breakdown rates or amino acid oxidation rates. These findings demonstrate that the magnitude and duration of the anabolic response to protein ingestion is not restricted and has previously been underestimated in vivo in humans.

Higher Muscle Protein Synthesis Rates Following Ingestion of an Omnivorous Meal Compared with an Isocaloric and Isonitrogenous Vegan Meal in Healthy, Older Adults.

BACKGROUND: Plant-derived proteins are considered to have fewer anabolic properties when compared with animal-derived proteins. The anabolic properties of isolated proteins do not necessarily reflect the anabolic response to the ingestion of whole foods. The presence or absence of the various components that constitute the whole-food matrix can strongly impact protein digestion and amino acid absorption and, as such, modulate postprandial muscle protein synthesis rates. So far, no study has compared the anabolic response following ingestion of an omnivorous compared with a vegan meal. OBJECTIVES: This study aimed to compare postprandial muscle protein synthesis rates following ingestion of a whole-food omnivorous meal providing 100 g lean ground beef with an isonitrogenous, isocaloric whole-food vegan meal in healthy, older adults. METHODS: In a randomized, counter-balanced, cross-over design, 16 older (65-85 y) adults (8 males, 8 females) underwent 2 test days. On one day, participants consumed a whole-food omnivorous meal containing beef as the primary source of protein (0.45 g protein/kg body mass; MEAT). On the other day, participants consumed an isonitrogenous and isocaloric whole-food vegan meal (PLANT). Primed continuous L-[ring-13C6]-phenylalanine infusions were applied with blood and muscle biopsies being collected frequently for 6 h to assess postprandial plasma amino acid profiles and muscle protein synthesis rates. Data are presented as means ± standard deviations and were analyzed by 2 way-repeated measures analysis of variance and paired-samples t tests. RESULTS: MEAT increased plasma essential amino acid concentrations more than PLANT over the 6-h postprandial period (incremental area under curve 87 ± 37 compared with 38 ± 54 mmol·6 h/L, respectively; P-interaction < 0.01). Ingestion of MEAT resulted in ∼47% higher postprandial muscle protein synthesis rates when compared with the ingestion of PLANT (0.052 ± 0.023 and 0.035 ± 0.021 %/h, respectively; paired-samples t test: P = 0.037). CONCLUSIONS: Ingestion of a whole-food omnivorous meal containing beef results in greater postprandial muscle protein synthesis rates when compared with the ingestion of an isonitrogenous whole-food vegan meal in healthy, older adults. This study was registered at clinicaltrials.gov as NCT05151887.

Trabecular, but not cortical, bone tissue protein synthesis rates are lower in the femoral head when compared to the proximal femur following an intracapsular hip fracture.

BACKGROUND: All musculoskeletal tissues are in a constant state of turnover, with a dynamic equilibrium between tissue protein synthesis and breakdown rates. The synthesis of protein allows musculoskeletal tissues to heal following injury. Yet, impaired tissue healing is observed following certain injuries, such as geriatric hip fractures. It is assumed that the regenerative properties of femoral head bone tissue are compromised following an intracapsular hip fracture and therefore hip replacement surgery is normally performed. However, the actual impact on in vivo bone protein synthesis rates has never been determined. DESIGN: In the present study, 10 patients (age: 79 ± 10 y, BMI: 24 ± 4 kg/m2) with an acute (<24 h) intracapsular hip fracture received a primed continuous intravenous infusion of L-[ring-13C6]-phenylalanine before and throughout their hip replacement surgery. Trabecular and cortical bone tissue from both the femoral head and proximal femur were sampled during surgery to assess protein synthesis rates of affected (femoral head) and unaffected (proximal femur) bone tissue, respectively. In addition, tissue samples of gluteus maximus muscle, synovium, ligamentum teres, and femoral head cartilage were collected. Tissue-specific protein synthesis rates were assessed by measuring L-[ring-13C6]-phenylalanine incorporation in tissue protein. RESULTS: Femoral head trabecular bone protein synthesis rates (0.056 [0.024-0.086] %/h) were lower when compared to proximal femur trabecular bone protein synthesis rates (0.081 [0.056-0.118] %/h; P = 0.043). Cortical bone protein synthesis rates did not differ between the femoral head and proximal femur (0.041 [0.021-0.078] and 0.045 [0.028-0.073] %/h, respectively; P > 0.05). Skeletal muscle, synovium, ligamentum teres, and femoral head cartilage protein synthesis rates averaged 0.080 [0.048-0.089], 0.093 [0.051-0.130], 0.121 [0.110-0.167], and 0.023 [0.015-0.039] %/h, respectively. CONCLUSION: In contrast to the general assumption that the femoral head is avital after an intracapsular displaced hip fracture in the elderly, our data show that bone protein synthesis is still ongoing in femoral head bone tissue during the early stages following an intracapsular hip fracture in older patients. Nonetheless, trabecular bone protein synthesis rates are lower in the femoral head when compared to the proximal femur in older patients following an acute intracapsular hip fracture. Trial register no: NL9036.

Branched-chain ketoacid co-ingestion with protein lowers amino acid oxidation during hemodialysis: A randomized controlled cross-over trial.

BACKGROUND & AIMS: Hemodialysis removes amino acids from the circulation, thereby stimulating muscle proteolysis. Protein ingestion during hemodialysis can compensate for amino acid removal but may also increase uremic toxin production. Branched-chain ketoacid (BCKA) co-ingestion may provide an additional anabolic stimulus without adding to uremic toxin accumulation. In the present study we assessed the impact of BCKA co-ingestion with protein on forearm amino acid balance and amino acid oxidation during hemodialysis. METHODS: Nine patients (age: 73 ± 10 y) on chronic hemodialysis participated in this crossover trial. During two 4-h hemodialysis sessions, patients ingested 18 g protein with (PRO + BCKA) or without (PRO) 9 g BCKAs in a randomized order. Test beverages were labeled with L-[ring-13C6]-phenylalanine and provided throughout the last 3 h of hemodialysis as 18 equal sips consumed with 10-min intervals. Arterial and venous plasma as well as breath samples were collected frequently throughout hemodialysis. RESULTS: Arterial plasma total amino acid (TAA) concentrations during PRO and PRO + BCKA treatments were significantly lower after 1 h of hemodialysis (2.6 ± 0.3 and 2.6 ± 0.3 mmol/L, respectively) when compared to pre-hemodialysis concentrations (4.2 ± 1.0 and 4.0 ± 0.5 mmol/L, respectively; time effect: P < 0.001). Arterial plasma TAA concentrations increased throughout test beverage ingestion (time effect: P = 0.027) without differences between treatments (time∗treatment: P = 0.62). Forearm arteriovenous TAA balance during test beverage ingestion did not differ between timepoints (time effect: P = 0.31) or treatments (time∗treatment: P = 0.34). Whole-body phenylalanine oxidation was 33 ± 16% lower during PRO + BCKA when compared to PRO treatments (P < 0.001). CONCLUSIONS: BCKA co-ingestion with protein during hemodialysis does not improve forearm net protein balance but lowers amino acid oxidation.

Pre-sleep Protein Ingestion Increases Mitochondrial Protein Synthesis Rates During Overnight Recovery from Endurance Exercise: A Randomized Controlled Trial.

BACKGROUND: Casein protein ingestion prior to sleep has been shown to increase myofibrillar protein synthesis rates during overnight sleep. It remains to be assessed whether pre-sleep protein ingestion can also increase mitochondrial protein synthesis rates. Though it has been suggested that casein protein may be preferred as a pre-sleep protein source, no study has compared the impact of pre-sleep whey versus casein ingestion on overnight muscle protein synthesis rates. OBJECTIVE: We aimed to assess the impact of casein and whey protein ingestion prior to sleep on mitochondrial and myofibrillar protein synthesis rates during overnight recovery from a bout of endurance-type exercise. METHODS: Thirty-six healthy young men performed a single bout of endurance-type exercise in the evening (19:45 h). Thirty minutes prior to sleep (23:30 h), participants ingested 45 g of casein protein, 45 g of whey protein, or a non-caloric placebo. Continuous intravenous L-[ring-13C6]-phenylalanine infusions were applied, with blood and muscle tissue samples being collected to assess overnight mitochondrial and myofibrillar protein synthesis rates. RESULTS: Pooled protein ingestion resulted in greater mitochondrial (0.087 ± 0.020 vs 0.067 ± 0.016%·h-1, p = 0.005) and myofibrillar (0.060 ± 0.014 vs 0.047 ± 0.011%·h-1, p = 0.012) protein synthesis rates when compared with placebo. Casein and whey protein ingestion did not differ in their capacity to stimulate mitochondrial (0.082 ± 0.019 vs 0.092 ± 0.020%·h-1, p = 0.690) and myofibrillar (0.056 ± 0.009 vs 0.064 ± 0.018%·h-1, p = 0.440) protein synthesis rates. CONCLUSIONS: Protein ingestion prior to sleep increases both mitochondrial and myofibrillar protein synthesis rates during overnight recovery from exercise. The overnight muscle protein synthetic response to whey and casein protein does not differ. CLINICAL TRIAL REGISTRATION: NTR7251 .

Acute Quark Ingestion Increases Muscle Protein Synthesis Rates at Rest with a Further Increase after Exercise in Young and Older Adult Males in a Parallel-Group Intervention Trial.

BACKGROUND: Ingestion of protein concentrates or isolates increases muscle protein synthesis rates in young and older adults. There is far less information available on the anabolic response following the ingestion of dairy wholefoods, which are commonly consumed in a normal diet. OBJECTIVES: This study investigates whether ingestion of 30 g protein provided as quark increases muscle protein synthesis rates at rest and whether muscle protein synthesis rates are further increased after resistance exercise in young and older adult males. METHODS: In this parallel-group intervention trial, 14 young (18-35 y) and 15 older (65-85 y) adult males ingested 30 g protein provided as quark after a single-legged bout of resistance exercise on leg press and leg extension machines. Primed, continuous intravenous L-[ring-13C6]-phenylalanine infusions were combined with the collection of blood and muscle tissue samples to assess postabsorptive and 4-h postprandial muscle protein synthesis rates at rest and during recovery from exercise. Data represent means ± SDs; η2 was used to measure the effect size. RESULTS: Plasma total amino acid and leucine concentrations increased after quark ingestion in both groups (both time: P < 0.001; η2 > 0.8), with no differences between groups (time × group: P = 0.127 and P = 0.172, respectively; η2<0.1). Muscle protein synthesis rates increased following quark ingestion at rest in both young (from 0.030 ± 0.011 to 0.051 ± 0.011 %·h-1) and older adult males (from 0.036 ± 0.011 to 0.062 ± 0.013 %·h-1), with a further increase in the exercised leg (to 0.071 ± 0.023 %·h-1 and to 0.078 ± 0.019 %·h-1, respectively; condition: P < 0.001; η2 = 0.716), with no differences between groups (condition × group: P = 0.747; η2 = 0.011). CONCLUSIONS: Quark ingestion increases muscle protein synthesis rates at rest with a further increase following exercise in both young and older adult males. The postprandial muscle protein synthetic response following quark ingestion does not differ between healthy young and older adult males when an ample amount of protein is ingested. This trial was registered at the Dutch Trial register, which is accessible via trialsearch.who.int www.trialregister.nl as NL8403.

Intradialytic Protein Ingestion and Exercise do Not Compromise Uremic Toxin Removal Throughout Hemodialysis.

OBJECTIVE: Dietary protein and physical activity interventions are increasingly implemented during hemodialysis to support muscle maintenance in patients with end-stage renal disease (ESRD). Although muscle maintenance is important, adequate removal of uremic toxins throughout hemodialysis is the primary concern for patients. It remains to be established whether intradialytic protein ingestion and/or exercise modulate uremic toxin removal during hemodialysis. METHODS: We recruited 10 patients with ESRD (age: 65 ± 16 y, BMI: 24.2 ± 4.8 kg/m2) on chronic hemodialysis treatment to participate in this randomized cross-over trial. During hemodialysis, patients were assigned to ingest 40 g protein or a nonprotein placebo both at rest (protein [PRO] and placebo [PLA], respectively) and following 30 min of exercise (PRO + exercise [EX] and PLA + EX, respectively). Blood and spent dialysate samples were collected throughout hemodialysis to assess reduction ratios and removal of urea, creatinine, phosphate, cystatin C, and indoxyl sulfate. RESULTS: The reduction ratios of urea and indoxyl sulfate were higher during PLA (76 ± 6% and 46 ± 9%, respectively) and PLA + EX interventions (77 ± 5% and 45 ± 10%, respectively) when compared to PRO (72 ± 4% and 40 ± 8%, respectively) and PRO + EX interventions (73 ± 4% and 43 ± 7%, respectively; protein effect: P = .001 and P = .023, respectively; exercise effect: P = .25 and P = .52, respectively). Nonetheless, protein ingestion resulted in greater urea removal (P = .046) during hemodialysis. Reduction ratios and removal of creatinine, phosphate, and cystatin C during hemodialysis did not differ following intradialytic protein ingestion or exercise (protein effect: P > .05; exercise effect: P>.05). Urea, creatinine, and phosphate removal were greater throughout the period with intradialytic exercise during PLA + EX and PRO + EX interventions when compared to the same period during PLA and PRO interventions (exercise effect: P = .034, P = .039, and P = .022, respectively). CONCLUSION: The removal of uremic toxins is not compromised by protein feeding and/or exercise implementation during hemodialysis in patients with ESRD.

Potato Protein Ingestion Increases Muscle Protein Synthesis Rates at Rest and during Recovery from Exercise in Humans.

INTRODUCTION: Plant-derived proteins have received considerable attention as an alternative to animal-based proteins and are now frequently used in both plant-based diets and sports nutrition products. However, little information is available on the anabolic properties of potato-derived protein. This study compares muscle protein synthesis rates after the ingestion of 30 g potato protein versus 30 g milk protein at rest and during recovery from a single bout of resistance exercise in healthy, young males. METHODS: In a randomized, double-blind, parallel-group design, 24 healthy young males (24 ± 4 yr) received primed continuous l -[ ring - 13 C 6 ]-phenylalanine infusions while ingesting 30 g potato-derived protein or 30 g milk protein after a single bout of unilateral resistance exercise. Blood and muscle biopsies were collected for 5 h after protein ingestion to assess postprandial plasma amino acid profiles and mixed muscle protein synthesis rates at rest and during recovery from exercise. RESULTS: Ingestion of both potato and milk protein increased mixed muscle protein synthesis rates when compared with basal postabsorptive values (from 0.020% ± 0.011% to 0.053% ± 0.017%·h -1 and from 0.021% ± 0.014% to 0.050% ± 0.012%·h -1 , respectively; P < 0.001), with no differences between treatments ( P = 0.54). In the exercised leg, mixed muscle protein synthesis rates increased to 0.069% ± 0.019% and 0.064% ± 0.015%·h -1 after ingesting potato and milk protein, respectively ( P < 0.001), with no differences between treatments ( P = 0.52). The muscle protein synthetic response was greater in the exercised compared with the resting leg ( P < 0.05). CONCLUSIONS: Ingestion of 30 g potato protein concentrate increases muscle protein synthesis rates at rest and during recovery from exercise in healthy, young males. Muscle protein synthesis rates after the ingestion of 30 g potato protein do not differ from rates observed after ingesting an equivalent amount of milk protein.

Cheese Ingestion Increases Muscle Protein Synthesis Rates Both at Rest and During Recovery from Exercise in Healthy, Young Males: A Randomized Parallel-Group Trial.

BACKGROUND: Protein ingestion increases muscle protein synthesis rates. The food matrix in which protein is provided can strongly modulate the postprandial muscle protein synthetic response. So far, the muscle protein synthetic response to the ingestion of whole foods remains largely unexplored. OBJECTIVES: To compare the impact of ingesting 30 g protein provided as milk protein or cheese on postprandial plasma amino acid concentrations and muscle protein synthesis rates at rest and during recovery from exercise in vivo in young males. METHODS: In this randomized, parallel-group intervention trial, 20 healthy males aged 18-35 y ingested 30 g protein provided as cheese or milk protein concentrate following a single-legged resistance-type exercise session consisting of 12 sets of leg press and leg extension exercises. Primed, continuous intravenous L-[ring-13C6]-phenylalanine infusions were combined with the collection of blood and muscle tissue samples to assess postabsorptive and 4-h postprandial muscle protein synthesis rates at rest and during recovery from exercise. Data were analyzed using repeated measures Time × Group (× Leg) ANOVA. RESULTS: Plasma total amino acid concentrations increased after protein ingestion (Time: P < 0.001), with 38% higher peak concentrations following milk protein than cheese ingestion (Time × Group: P < 0.001). Muscle protein synthesis rates increased following both cheese and milk protein ingestion from 0.037 ± 0.014 to 0.055 ± 0.018%·h-1 and 0.034 ± 0.008 to 0.056 ± 0.010%·h-1 at rest and even more following exercise from 0.031 ± 0.010 to 0.067 ± 0.013%·h-1 and 0.030 ± 0.008 to 0.063 ± 0.010%·h-1, respectively (Time: all P < 0.05; Time × Leg: P = 0.002), with no differences between cheese and milk protein ingestion (Time × Group: both P > 0.05). CONCLUSION: Cheese ingestion increases muscle protein synthesis rates both at rest and during recovery from exercise. The postprandial muscle protein synthetic response to the ingestion of cheese or milk protein does not differ when 30 g protein is ingested at rest or during recovery from exercise in healthy, young males.

Cheese Ingestion Increases Muscle Protein Synthesis Rates Both at Rest and During Recovery from Exercise in Healthy, Young Males: A Randomized Parallel-Group Trial.

BACKGROUND: Protein ingestion increases muscle protein synthesis rates. The food matrix in which protein is provided can strongly modulate the postprandial muscle protein synthetic response. So far, the muscle protein synthetic response to the ingestion of whole foods remains largely unexplored. OBJECTIVES: To compare the impact of ingesting 30 g protein provided as milk protein or cheese on postprandial plasma amino acid concentrations and muscle protein synthesis rates at rest and during recovery from exercise in vivo in young males. METHODS: In this randomized, parallel-group intervention trial, 20 healthy males aged 18-35 y ingested 30 g protein provided as cheese or milk protein concentrate following a single-legged resistance-type exercise session consisting of 12 sets of leg press and leg extension exercises. Primed, continuous intravenous L-[ring-13C6]-phenylalanine infusions were combined with the collection of blood and muscle tissue samples to assess postabsorptive and 4-h postprandial muscle protein synthesis rates at rest and during recovery from exercise. Data were analyzed using repeated measures Time × Group (× Leg) ANOVA. RESULTS: Plasma total amino acid concentrations increased after protein ingestion (Time: P < 0.001), with 38% higher peak concentrations following milk protein than cheese ingestion (Time × Group: P < 0.001). Muscle protein synthesis rates increased following both cheese and milk protein ingestion from 0.037 ± 0.014 to 0.055 ± 0.018%·h-1 and 0.034 ± 0.008 to 0.056 ± 0.010%·h-1 at rest and even more following exercise from 0.031 ± 0.010 to 0.067 ± 0.013%·h-1 and 0.030 ± 0.008 to 0.063 ± 0.010%·h-1, respectively (Time: all P < 0.05; Time × Leg: P = 0.002), with no differences between cheese and milk protein ingestion (Time × Group: both P > 0.05). CONCLUSION: Cheese ingestion increases muscle protein synthesis rates both at rest and during recovery from exercise. The postprandial muscle protein synthetic response to the ingestion of cheese or milk protein does not differ when 30 g protein is ingested at rest or during recovery from exercise in healthy, young males.

Amino acid removal during hemodialysis can be compensated for by protein ingestion and is not compromised by intradialytic exercise: a randomized controlled crossover trial.

BACKGROUND: Patients with end-stage renal disease (ESRD) undergoing hemodialysis experience a rapid decline in skeletal muscle mass and strength. Hemodialysis removes amino acids (AAs) from the circulation, thereby lowering plasma AA concentrations and stimulating proteolysis. OBJECTIVES: In the present study, we evaluate the impact of intradialytic protein ingestion at rest and following exercise on AA removal and plasma AA availability in patients with ESRD. METHODS: Ten patients (age: 65 ± 16 y, male/female: 8/2, BMI: 24.2 ± 4.8 kg/m2, serum albumin: 3.4 ± 0.3 g/dL) with ESRD undergoing hemodialysis participated in this randomized controlled crossover trial. During 4 hemodialysis sessions, patients were assigned to ingest 40 g protein or a placebo 60 min after initiation, both at rest (PRO and PLA, respectively) and following exercise (PRO + EX and PLA + EX, respectively). Spent dialysate and blood samples were collected every 30 min throughout hemodialysis to assess AA removal and plasma AA availability. RESULTS: Plasma AA concentrations declined by 26.1 ± 4.5% within 30 min after hemodialysis initiation during all interventions (P < 0.001, η2p > 0.79). Protein ingestion, but not intradialytic exercise, increased AA removal throughout hemodialysis (9.8 ± 2.0, 10.2 ± 1.6, 16.7 ± 2.2, and 17.3 ± 2.3 g during PLA, PLA + EX, PRO, and PRO + EX interventions, respectively; protein effect P < 0.001, η2p = 0.97; exercise effect P = 0.32, η2p = 0.11). Protein ingestion increased plasma AA concentrations until the end of hemodialysis, whereas placebo ingestion resulted in decreased plasma AA concentrations (time effect P < 0.001, η2p > 0.84). Plasma AA availability (incremental AUC) was greater during PRO and PRO + EX interventions (49 ± 87 and 70 ± 34 mmol/L/240 min, respectively) compared with PLA and PLA + EX interventions (-227 ± 54 and -208 ± 68 mmol/L/240 min, respectively; protein effect P < 0.001, η2p = 0.98; exercise effect P = 0.21, η2p = 0.16). CONCLUSIONS: Protein ingestion during hemodialysis compensates for AA removal and increases plasma AA availability both at rest and during recovery from intradialytic exercise. Intradialytic exercise does not compromise AA removal or reduce plasma AA availability during hemodialysis in a postabsorptive or postprandial state.

No differences in muscle protein synthesis rates following ingestion of wheat protein, milk protein, and their protein blend in healthy, young males.

Plant-derived proteins have been suggested to have less anabolic properties when compared with animal-derived proteins. Whether blends of plant- and animal-derived proteins can compensate for their lesser anabolic potential has not been assessed. The present study compares post-prandial muscle protein synthesis rates following the ingestion of milk protein with wheat protein or a blend of wheat plus milk protein in healthy, young males. In a randomised, double-blind, parallel-group design, 36 males (23 (sd 3) years) received a primed continuous L-[ring-13C6]-phenylalanine infusion after which they ingested 30 g milk protein (MILK), 30 g wheat protein (WHEAT) or a 30 g blend combining 15 g wheat plus 15 g milk protein (WHEAT+MILK). Blood and muscle biopsies were collected frequently for 5 h to assess post-prandial plasma amino acid profiles and subsequent myofibrillar protein synthesis rates. Ingestion of protein increased myofibrillar protein synthesis rates in all treatments (P < 0·001). Post-prandial myofibrillar protein synthesis rates did not differ between MILK v. WHEAT (0·053 (sd 0·013) v. 0·056 (sd 0·012) %·h-1, respectively; t test P = 0·56) or between MILK v. WHEAT+MILK (0·053 (sd 0·013) v. 0·059 (sd 0·025) %·h-1, respectively; t test P = 0·46). In conclusion, ingestion of 30 g milk protein, 30 g wheat protein or a blend of 15 g wheat plus 15 g milk protein increases muscle protein synthesis rates in young males. Furthermore, muscle protein synthesis rates following the ingestion of 30 g milk protein do not differ from rates observed after ingesting 30 g wheat protein or a blend with 15 g milk plus 15 g wheat protein in healthy, young males.

Dietary protein interventions to improve nutritional status in end-stage renal disease patients undergoing hemodialysis.

PURPOSE OF REVIEW: Poor nutritional status is prevalent among end-stage renal disease patients undergoing hemodialysis. Chronic hemodialysis patients show an accelerated decline in skeletal muscle mass and strength, which is associated with higher mortality rates and a reduced quality of life. The current review aims to summarize recent advances regarding underlying causes of muscle loss and interventions that support muscle mass maintenance in patients with chronic hemodialysis. RECENT FINDINGS: Muscle maintenance in chronic hemodialysis patients is compromised by low dietary protein intake levels, anabolic resistance of skeletal muscle tissue, sedentary behavior, and amino acid removal during hemodialysis. Studies assessing the effect of increased protein intake on nutritional status generally show beneficial results, especially in hypoalbuminemic chronic hemodialysis patients. The muscle protein synthetic response following protein ingestion in chronic hemodialysis patients may be enhanced through incorporation of structured physical activity and/or concurrent ketoacid ingestion. SUMMARY: A coordinated program that combines nutritional and physical activity interventions is likely required to attenuate the decline in muscle mass and strength of chronic hemodialysis patients. Nephrologists, dieticians, and exercise specialists should collaborate closely to establish guidelines regarding the appropriate quantity and timing of protein ingestion. In addition, they should provide tailored nutritional and physical activity interventions for chronic hemodialysis patients (see video, Supplemental Digital Content 1, Video abstract, http://links.lww.com/COCN/A14).

End-Stage Renal Disease Patients Lose a Substantial Amount of Amino Acids during Hemodialysis.

BACKGROUND: Poor nutritional status is frequently observed in end-stage renal disease patients and associated with adverse clinical outcomes and increased mortality. Loss of amino acids (AAs) during hemodialysis (HD) may contribute to protein malnutrition in these patients. OBJECTIVE: We aimed to assess the extent of AA loss during HD in end-stage renal disease patients consuming their habitual diet. METHODS: Ten anuric chronic HD patients (mean ± SD age: 67.9 ± 19.3 y, BMI: 23.2 ± 3.5 kg/m2), undergoing HD 3 times per week, were selected to participate in this study. Spent dialysate was collected continuously and plasma samples were obtained directly before and after a single HD session in each participant. AA profiles in spent dialysate and in pre-HD and post-HD plasma were measured through ultra-performance liquid chromatography to determine AA concentrations and, as such, net loss of AAs. In addition, dietary intake before and throughout HD was assessed using a 24-h food recall questionnaire during HD. Paired-sample t tests were conducted to compare pre-HD and post-HD plasma AA concentrations. RESULTS: During an HD session, 11.95 ± 0.69 g AAs were lost via the dialysate, of which 8.26 ± 0.46 g were nonessential AAs, 3.69 ± 0.31 g were essential AAs, and 1.64 ± 0.17 g were branched-chain AAs. As a consequence, plasma total and essential AA concentrations declined significantly from 2.88 ± 0.15 and 0.80 ± 0.05 mmol/L to 2.27 ± 0.11 and 0.66 ± 0.05 mmol/L, respectively (P < 0.05). AA profiles of pre-HD plasma and spent dialysate were similar. Moreover, AA concentrations in pre-HD plasma and spent dialysate were strongly correlated (Spearman's ρ = 0.92, P < 0.001). CONCLUSIONS: During a single HD session, ∼12 g AAs are lost into the dialysate, causing a significant decline in plasma AA concentrations. AA loss during HD can contribute substantially to protein malnutrition in end-stage renal disease patients. This study was registered at the Netherlands Trial Registry (NTR7101).

Dietary Protein and Physical Activity Interventions to Support Muscle Maintenance in End-Stage Renal Disease Patients on Hemodialysis.

End-stage renal disease patients have insufficient renal clearance capacity left to adequately excrete metabolic waste products. Hemodialysis (HD) is often employed to partially replace renal clearance in these patients. However, skeletal muscle mass and strength start to decline at an accelerated rate after initiation of chronic HD therapy. An essential anabolic stimulus to allow muscle maintenance is dietary protein ingestion. Chronic HD patients generally fail to achieve recommended protein intake levels, in particular on dialysis days. Besides a low protein intake on dialysis days, the protein equivalent of a meal is extracted from the circulation during HD. Apart from protein ingestion, physical activity is essential to allow muscle maintenance. Unfortunately, most chronic HD patients have a sedentary lifestyle. Yet, physical activity and nutritional interventions to support muscle maintenance are generally not implemented in routine patient care. To support muscle maintenance in chronic HD patients, quantity and timing of protein intake should be optimized, in particular throughout dialysis days. Furthermore, implementing physical activity either during or between HD sessions may improve the muscle protein synthetic response to protein ingestion. A well-orchestrated combination of physical activity and nutritional interventions will be instrumental to preserve muscle mass in chronic HD patients.

Exercising to offset muscle mass loss in hemodialysis patients: The disconnect between intention and intervention.

Skeletal muscle loss is the most important hallmark of protein energy wasting syndrome as it contributes to declines in physical independence, poor quality of life, and higher mortality risk in individuals with ESRD on maintenance hemodialysis (HD). As such, exercise and nutritional interventions have been investigated with the goal to preserve skeletal muscle mass and overall quality of life. Unfortunately, current efforts are unable to confirm the capacity of exercise to mitigate ESRD-associated muscle wasting. However, the inconclusive data are often accompanied by suboptimal exercise prescriptions. Exercise sessions are often implemented in-clinic during the catabolic and proinflammatory period of dialysis treatment and without concurrent nutritional support. Additionally, indirect considerations like exercise intolerance and exercise program compliance/adherence also inhibit exercise training potential. These shortcomings all stem from the current lack of understanding in skeletal muscle mass regulation within the context of ESRD and intermittent HD. As such, this review summarizes the current understanding of exercise regulation on skeletal muscle mass and ESRD-related obstacles of anabolism to contextualize the ineffectiveness of current exercise interventions for HD patients.