Casein Intake Research Articles

Ingestion of Casein in a Milk Matrix Modulates Dietary Protein Digestion and Absorption Kinetics but Does Not Modulate Postprandial Muscle Protein Synthesis in Older Men1–3

Background: The slow digestion and amino acid absorption kinetics of isolated micellar casein have been held responsible for its relatively lower postprandial muscle protein synthetic response compared with rapidly digested proteins such as isolated whey. However, casein is normally consumed within a milk matrix. We hypothesized that protein digestion and absorption kinetics and the subsequent muscle protein synthetic response after micellar casein ingestion are modulated by the milk matrix.Objective: The aim of this study was to determine the impact of a milk matrix on casein protein digestion and absorption kinetics and postprandial muscle protein synthesis in older men.Methods: In a parallel-group design, 32 healthy older men (aged 71 ± 1 y) received a primed continuous infusion of L-[ring-2H5]-phenylalanine, L-[ring-3,5-2H2]-tyrosine, and L-[1-13C]-leucine, and ingested 25 g intrinsically L-[1-13C]-phenylalanine and L-[1-13C]-leucine labeled casein dissolved in bovine milk serum (Cas+Serum) or water (Cas). Plasma samples and muscle biopsies were collected in the postabsorptive state and for 300 min in the postprandial period to examine whole-body and skeletal muscle protein metabolism.Results: Casein ingestion increased plasma leucine and phenylalanine concentrations and L-[1-13C]-phenylalanine enrichments, with a more rapid rise after Cas vs. Cas+Serum. Nonetheless, dietary protein–derived phenylalanine availability did not differ between Cas+Serum (47 ± 2%, mean ± SEM) and Cas (46 ± 3%) when assessed over the 300-min postprandial period (P = 0.80). The milk matrix did not modulate postprandial myofibrillar protein synthesis rates from 0 to 120 min (0.038 ± 0.005 vs. 0.031 ± 0.007%/h) or from 120 to 300 min (0.052 ± 0.004 vs. 0.067 ± 0.005%/h) after Cas+Serum vs. Cas. Similarly, no treatment differences in muscle protein–bound L-[1-13C]-phenylalanine enrichments were observed at 120 min (0.003 ± 0.001 vs. 0.002 ± 0.001) or 300 min (0.015 ± 0.002 vs. 0.016 ± 0.002 mole percent excess) after Cas+Serum vs. Cas.Conclusions: Casein ingestion in a milk matrix delays protein digestion and absorption but does not modulate postprandial muscle protein synthesis when compared to the ingestion of micellar casein only in healthy older men. This trial was registered at Nederlands Trial Register as NTR4429.

Change of gene expression on protein uptake composition and hindlimb-suspension in rat skeletal muscle.

[Purpose]This study was to investigate changes in BCAT and BCKDH genes by Hindlimb-Suspension (HS) and protein intake composition (casein, Whey protein) in rats.[Methods]Following 5-day preliminary feeding, forty-eight male 5 weeks old Sprague Dawley albino rats (110g) divided into 17% protein intake group (24 rats) and 30% protein intake group (24 rats), and each group divided further into Hindlimb-Suspension group (HS; 12 rats) and control group(CON; 12 rats). Eventually, this study was performed with Whey protein intake group (HS; 6 rats, CON; 6 rats) and casein intake group (HS; 6 rats, CON; 6 rats). For analysis purposes, total RNA was extracted from isolated skeletal muscles, and mRNA expression was analyzed using Real Time PCR. Two-way ANOVA was performed to examine the difference in BCATm and BCKDH mRNA expression on protein uptake and myoatrophy. post-hoc test was perform on interaction if any, and significance level was set at p<0.05.[Results]In this study, BCATm and BCKDH gene analysis in rat skeletal muscles by hindlimb-suspension and protein intake composition resulted in significant higher BCATm expression in 30% dietary protein group and hindlimb-suspension group that control group. In addition, regarding BCKDH, BCKDH was significantly higher in hindlimb-suspended 30% protein intake group than control group.[Conclusion]Overall, protein intake and myoatrophy demonstrated close relationship in skeletal muscles. Therefore, it is likely to affect effectively in prevention or recovery of exercise induced muscle disorder. This effect is considered to be applied to maintain and improve health of not only athletes but also the general public. Additionally it would be applied in convalescent rehabilitation due to skeletal muscle atrophy.

A mixture of cod and scallop protein reduces adiposity and improves glucose tolerance in high-fat fed male C57BL/6J mice.

Low-protein and high-protein diets regulate energy metabolism in animals and humans. To evaluate whether different dietary protein sources modulate energy balance when ingested at average levels obesity-prone male C57BL/6J mice were pair-fed high-fat diets (67 energy percent fat, 18 energy percent sucrose and 15 energy percent protein) with either casein, chicken filet or a mixture of cod and scallop (1∶1 on amino acid content) as protein sources. At equal energy intake, casein and cod/scallop fed mice had lower feed efficiency than chicken fed mice, which translated into reduced adipose tissue masses after seven weeks of feeding. Chicken fed mice had elevated hepatic triglyceride relative to casein and cod/scallop fed mice and elevated 4 h fasted plasma cholesterol concentrations compared to low-fat and casein fed mice. In casein fed mice the reduced adiposity was likely related to the observed three percent lower apparent fat digestibility compared to low-fat, chicken and cod/scallop fed mice. After six weeks of feeding an oral glucose tolerance test revealed that despite their lean phenotype, casein fed mice had reduced glucose tolerance compared to low-fat, chicken and cod/scallop fed mice. In a separate set of mice, effects on metabolism were evaluated by indirect calorimetry before onset of diet-induced obesity. Spontaneous locomotor activity decreased in casein and chicken fed mice when shifting from low-fat to high-fat diets, but cod/scallop feeding tended (P = 0.06) to attenuate this decrease. Moreover, at this shift, energy expenditure decreased in all groups, but was decreased to a greater extent in casein fed than in cod/scallop fed mice, indicating that protein sources regulated energy expenditure differently. In conclusion, protein from different sources modulates energy balance in C57BL/6J mice when given at normal levels. Ingestion of a cod/scallop-mixture prevented diet-induced obesity compared to intake of chicken filet and preserved glucose tolerance compared to casein intake.

Whey Protein Delays Gastric Emptying and Suppresses Plasma Fatty Acids and Their Metabolites Compared to Casein, Gluten, and Fish Protein

Whey protein has been demonstrated to improve fasting lipid and insulin response in overweight and obese individuals. To establish new hypotheses for this effect and to investigate the impact of stomach emptying, we compared plasma profiles after intake of whey isolate (WI), casein, gluten (GLU), and cod (COD). Obese, nondiabetic subjects were included in the randomized, blinded, crossover meal study. Subjects ingested a high fat meal containing one of the four protein sources. Plasma samples were collected at five time points and metabolites analyzed using LC-Q-TOF-MS. In contrast to previous studies, the WI meal caused a decreased rate of gastric emptying compared to the other test meals. The WI meal also caused elevated levels of a number of amino acids, possibly stimulating insulin release leading to reduced plasma glucose. The WI meal also caused decreased levels of a number of fatty acids, while the GLU meal caused elevated levels of a number of unidentified hydroxy fatty acids and dicarboxylic fatty acids. Also reported are a number of markers of fish intake unique to the COD meal.

Multi-block PCA and multi-compartmental study of the metabolic responses to intake of hydrolysed versus intact casein in C57BL/6J mice by NMR-based metabolomics

Recently we showed that exchanging intact casein with extensively hydrolysed casein in Western diets prevented diet-induced obesity in obesity-prone C57BL/6J mice. To gain further insight into the underlying mechanisms for the metabolic alterations induced by intake of hydrolysed casein, we performed an exploratory investigation using proton NMR spectroscopy, multi-block PCA (MBPCA) and a multi-compartment model including analyses of plasma, urine, faeces and tissue samples from mice fed diets with intact or hydrolysed casein and 16 or 32 energy% protein. The MBPCA superscores showed a clear separation between samples from mice fed intact and hydrolysed casein diets, respectively. Block loadings revealed that fecal fat content was higher, and tissue and plasma lipid levels were lower in mice fed hydrolysed casein diets compared with mice fed intact casein. Amino acid metabolism was also altered by dietary protein form, and levels of branched-chain amino acids were higher in faeces and urine and lower in plasma and spleen in mice fed hydrolysed protein. Moreover, hepatic levels of the sulphur-containing metabolites taurine and glutathione were increased in mice fed hydrolysed casein, and hepatic glycogen amount was increased in mice fed hydrolysed casein. In contrast, the levels of glucose and its metabolite lactate were reduced in faeces, liver and plasma. Taken together, NMR-based metabolomic analyses indicated that pathways within lipid, amino acid and carbohydrate metabolism were altered by intake of hydrolysed casein, and that these alterations are likely to be underlying mechanisms for the observed prevention against diet-induced obesity associated with hydrolysed casein intake.

Development of double blind gluten &amp; casein free (GFCF) test foods for autism trial

Methods A company, developed a range of test foods muffins, porridge, batter mix, lemon & almond cookies and chocolate krispie bars, containing the estimated average habitual child intake of gluten (5g) and/or casein (5g): Gluten and casein added (GACA); Added casein only (GFCA); Added gluten only (GACF). No gluten or casein added (GFCF). We aimed to recruit 60 children (3-6 yrs) with autism and to randomly allocate them to receive test foods from one the above groups (labelled A-D to maintain blinding) for 28 days alongside normal diet. Outcomes were measured by food consumption diaries, a test foods acceptability questionnaire and telephone interviews with a sub-set of parents.

Hydrolyzed Casein Reduces Diet-Induced Obesity in Male C57BL/6J Mice

The digestion rate of dietary protein is a regulating factor for postprandial metabolism both in humans and animal models. However, few data exist about the habitual consumption of proteins with different digestion rates with regard to the development of body mass and diet-induced obesity. Here, we used a factorial ANOVA design to investigate the effects of protein form (intact vs. hydrolyzed casein) and protein level (16 vs. 32 energy percent protein) on body mass gain and adiposity in obesity-prone male C57BL/6J mice fed Western diets with 35 energy percent fat. Mice fed the hydrolyzed casein diets had higher spontaneous locomotor activity than mice fed intact casein. During the light phase, mice fed hydrolyzed casein tended (P = 0.08) to have a lower respiratory exchange ratio, indicating lower utilization of carbohydrates as energy substrate relative to those fed intact casein. In further support of less carbohydrate oxidation, plasma concentrations of glucose and those of the glucose metabolite lactate were lower in fed mice that consumed the hydrolyzed compared with the intact casein diet. Concomitantly, the plasma insulin concentration was strongly reduced in fed mice given hydrolyzed casein relative to those given intact casein. The mice fed hydrolyzed casein had greater ex vivo inguinal white adipose tissue non-CO2 β-oxidation capacity along with induced expression of genes involved in mitochondrial fatty acid oxidation and mitochondrial uncoupling. The physiological changes induced by hydrolyzed casein ingestion translated into decreased body and adipose tissue masses. We conclude that chronic consumption of extensively hydrolyzed casein reduces body mass gain and diet-induced obesity in male C57BL/6J mice.

Sequential release of milk protein–derived bioactive peptides in the jejunum in healthy humans

The digestive hydrolysis of dietary proteins leads to the release of peptides in the intestinal tract, where they may exert a variety of functions, but their characterization and quantification are difficult. We aimed to characterize and determine kinetics of the formation of peptides present in the jejunum of humans who ingested casein or whey proteins by using mass spectrometry and to look for and quantify bioactive peptides. Subjects were equipped with a double-lumen nasogastric tube that migrated to the proximal jejunum. A sample collection was performed for 6 h after the ingestion of 30 g (15)N-labeled casein (n = 7) or whey proteins (WPs; n = 6). Nitrogen flow rates were measured, and peptides were identified by using mass spectrometry. After casein ingestion, medium-size peptides (750-1050 kDa) were released during 6 h, whereas larger peptides (1050-1800 kDa) were released from WPs in the first 3 h. A total of 356 and 146 peptides were detected and sequenced in the jejunum after casein and WP ingestion, respectively. β-casein was the most important precursor of peptides, including bioactive peptides with various activities. The amounts of β-casomorphins (β-casein 57-, 58-, 59-, and 60-66) and β-casein 108-113 released on the postprandial window were sufficient to elicit the biological action of these peptides (ie, opioid and antihypertensive, respectively). Clear evidence is shown of the presence of bioactive peptides in the jejunum of healthy humans who ingested casein. Our findings raise the question about the physiologic conditions under which these peptides can express their bioactivity in humans. This trial was registered at clinicaltrials.gov as NCT00862329.

Postprandial response of plasma IL-6 to isoenergetic meals rich in casein or potato singly and combined in obese women.

Milk consumption decreases inflammatory stress in overweight and obese subjects. Casein is the major protein in milk and enhances the secretion of insulin that has anti-inflammatory activity. The aim of the present study was to compare the acute effect of meals rich in casein and carbohydrate and a combination of both nutrients on postprandial plasma concentrations of IL-6, a marker of inflammation, in obese women. A total of twenty-five obese women aged 38-68 years consumed isoenergetic meals rich in potato (POT) or casein (CA) or a combination of both these meals (POT+CA), in random order in a cross-over trial. After an overnight fast, blood samples were collected before and at 1 and 4h after the meals and circulating concentrations of IL-6, glucose, insulin and NEFA were measured. Plasma IL-6 concentrations increased significantly (P<0·001) during 4h after the meals. The AUC of postprandial IL-6 concentrations was not significantly (P=0·77) different among the meals. Postprandial serum insulin concentration AUC was significantly higher during the POT+CA meal compared with the POT meal (P=0·001) and the CA meal (P<0·05), which in turn was significantly higher than the POT meal (P<0·05). These data show that while ingestion of CA alone or combined with POT acutely increases circulating insulin concentrations, it does not appreciably alter the postprandial increase in plasma IL-6 concentrations in obese women.

Casein improves brachial and central aortic diastolic blood pressure in overweight adolescents: a randomised, controlled trial.

Arterial stiffness, blood pressure (BP) and blood lipids may be improved by milk in adults and the effects may be mediated via proteins. However, limited is known about the effects of milk proteins on central aortic BP and no studies have examined the effects in children. Therefore, the present trial examined the effect of milk and milk proteins on brachial and central aortic BP, blood lipids, inflammation and arterial stiffness in overweight adolescents. A randomised controlled trial was conducted in 193 overweight adolescents aged 12-15 years. They were randomly assigned to drink 1 litre of water, skimmed milk, whey or casein for 12 weeks. The milk-based test drinks contained 35g protein/l. The effects were compared with the water group and a pretest control group consisting of thirty-two of the adolescents followed 12 weeks before the start of the intervention. Outcomes were brachial and central aortic BP, pulse wave velocity and augmentation index, serum C-reactive protein and blood lipids. Brachial and central aortic diastolic BP (DBP) decreased by 2·7% (P=0·036) and 2·6% (P=0·048), respectively, within the casein group and the changes were significantly different from those of the pretest control group (P=0·040 and P=0·034, respectively). There was a significant increase in central aortic DBP, and in brachial and central systolic BP in the whey group compared with the water group (P=0·003, P=0·009 and P=0·002, respectively). There were no changes in measures of arterial stiffness or blood lipid concentrations. A high intake of casein improves DBP in overweight adolescents. Thus, casein may be beneficial for younger overweight subjects in terms of reducing the long-term risk of CVD. In contrast, whey protein seems to increase BP compared with drinking water; however, water may be considered an active control group.

Variation in Fat, Lactose, and Protein Composition in Breast Milk over 24 Hours

Data regarding the association between breast milk composition and infant feeding patterns (frequency and amount of breast milk taken) would help in understanding the regulation of food intake in breastfed infants. This study examined the relationship between breast milk macronutrient concentration and patterns of milk intake in breastfeeding infants over a 24-hour breastfeeding period. Mothers of healthy term infants (n = 15) collected pre- and postfeed breast milk samples from each feed at each breast over a 24-hour period. Breast milk samples were analyzed for fat, lactose, total protein, casein, and whey protein content. The energy content for each feed was calculated. Breastfeeding patterns and milk composition varied greatly between individuals. The fat content of milk significantly differed over 24 hours (P = .01), whereas the concentration of lactose and protein content remained the same. The mean 24-hour total protein, whey, and casein intake was inversely (P < .01), whereas lactose concentration was positively (P = .03) related to the number of breast feeds per day. No relationship was seen either between fat or energy content and feeding patterns. The mean (SD) concentration of fat, lactose, and total protein over the 24-hour period was 43 (12) g/L, 68 (7) g/L, and 13 (2) g/L, respectively. The association between milk protein intake and the breastfeeding frequency suggests that the protein intake may play a role in infant appetite control.

Rapid aminoacidemia enhances myofibrillar protein synthesis and anabolic intramuscular signaling responses after resistance exercise

Ingestion of whey or casein yields divergent patterns of aminoacidemia that influence whole-body and skeletal muscle myofibrillar protein synthesis (MPS) after exercise. Direct comparisons of the effects of contrasting absorption rates exhibited by these proteins are confounded by their differing amino acid contents. Our objective was to determine the effect of divergent aminoacidemia by manipulating ingestion patterns of whey protein alone on MPS and anabolic signaling after resistance exercise. In separate trials, 8 healthy men consumed whey protein either as a single bolus (BOLUS; 25-g dose) or as repeated, small, "pulsed" drinks (PULSE; ten 2.5-g drinks every 20 min) to mimic a more slowly digested protein. MPS and phosphorylation of signaling proteins involved in protein synthesis were measured at rest and after resistance exercise. BOLUS increased blood essential amino acid (EAA) concentrations above those of PULSE (162% compared with 53%, P < 0.001) 60 min after exercise, whereas PULSE resulted in a smaller but sustained increase in aminoacidemia that remained elevated above BOLUS amounts later (180-220 min after exercise, P < 0.05). Despite an identical net area under the EAA curve, MPS was elevated to a greater extent after BOLUS than after PULSE early (1-3 h: 95% compared with 42%) and later (3-5 h: 193% compared with 121%) (both P < 0.05). There were greater changes in the phosphorylation of the Akt-mammalian target of rapamycin pathway after BOLUS than after PULSE. Rapid aminoacidemia in the postexercise period enhances MPS and anabolic signaling to a greater extent than an identical amount of protein fed in small pulses that mimic a more slowly digested protein. A pronounced peak aminoacidemia after exercise enhances protein synthesis. This trial was registered at clinicaltrials.gov as NCT01319513.

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

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. 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. 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. 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. 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.

Whey and casein labeled withl-[1-13C]leucine and muscle protein synthesis: effect of resistance exercise and protein ingestion

Muscle protein turnover following resistance exercise and amino acid availability are relatively well described. By contrast, the beneficial effects of different sources of intact proteins in relation to exercise need further investigation. Our objective was to compare muscle anabolic responses to a single bolus intake of whey or casein after performance of heavy resistance exercise. Young male individuals were randomly assigned to participate in two protein trials (n = 9) or one control trial (n = 8). Infusion of l-[1-(13)C]leucine was carried out, and either whey, casein (0.3 g/kg lean body mass), or a noncaloric control drink was ingested immediately after exercise. l-[1-(13)C]leucine-labeled whey and casein were used while muscle protein synthesis (MPS) was assessed. Blood and muscle tissue samples were collected to measure systemic hormone and amino acid concentrations, tracer enrichments, and myofibrillar protein synthesis. Western blots were used to investigate the Akt signaling pathway. Plasma insulin and branched-chain amino acid concentrations increased to a greater extent after ingestion of whey compared with casein. Myofibrillar protein synthesis was equally increased 1-6 h postexercise after whey and casein intake, both of which were higher compared with control (P < 0.05). Phosphorylation of Akt and p70(S6K) was increased after exercise and protein intake (P < 0.05), but no differences were observed between the types of protein except for total 4E-BP1, which was higher after whey intake than after casein intake (P < 0.05). In conclusion, whey and casein intake immediately after resistance exercise results in an overall equal MPS response despite temporal differences in insulin and amino acid concentrations and 4E-BP1.

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-[1-13C]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±38kg) were continuously infused with l-[1-13C]phenylalanine at 402 μmol/min for 44 to 48h, 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/m2) ingested 35g of casein highly enriched with [1-13C] phenylalanine. Plasma samples were collected at regular intervals, and skeletal muscle biopsies were collected before and 6h after casein ingestion. In the initial experiment, a total of 5.83kg of l-[1-13C]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 35g of intrinsically labeled casein resulted in peak plasma l-[1-13C]phenylalanine enrichments within 90min 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.

Ingestion of whey hydrolysate, casein, or soy protein isolate: effects on mixed muscle protein synthesis at rest and following resistance exercise in young men

This study was designed to compare the acute response of mixed muscle protein synthesis (MPS) to rapidly (i.e., whey hydrolysate and soy) and slowly (i.e., micellar casein) digested proteins both at rest and after resistance exercise. Three groups of healthy young men (n = 6 per group) performed a bout of unilateral leg resistance exercise followed by the consumption of a drink containing an equivalent content of essential amino acids (10 g) as either whey hydrolysate, micellar casein, or soy protein isolate. Mixed MPS was determined by a primed constant infusion of l-[ring-(13)C(6)]phenylalanine. Ingestion of whey protein resulted in a larger increase in blood essential amino acid, branched-chain amino acid, and leucine concentrations than either casein or soy (P < 0.05). Mixed MPS at rest (determined in the nonexercised leg) was higher with ingestion of faster proteins (whey = 0.091 +/- 0.015, soy = 0.078 +/- 0.014, casein = 0.047 +/- 0.008%/h); MPS after consumption of whey was approximately 93% greater than casein (P < 0.01) and approximately 18% greater than soy (P = 0.067). A similar result was observed after exercise (whey > soy > casein); MPS following whey consumption was approximately 122% greater than casein (P < 0.01) and 31% greater than soy (P < 0.05). MPS was also greater with soy consumption at rest (64%) and following resistance exercise (69%) compared with casein (both P < 0.01). We conclude that the feeding-induced simulation of MPS in young men is greater after whey hydrolysate or soy protein consumption than casein both at rest and after resistance exercise; moreover, despite both being fast proteins, whey hydrolysate stimulated MPS to a greater degree than soy after resistance exercise. These differences may be related to how quickly the proteins are digested (i.e., fast vs. slow) or possibly to small differences in leucine content of each protein.

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 producedl-[1-13C]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.

Whey Protein Ingestion Enhances Postprandial Anabolism during Short-Term Bed Rest in Young Men

We tested the relative ability of rapidly digested whey and slowly digested casein to stimulate net whole-body protein synthesis during prolonged physical inactivity. We studied 8 young male volunteers after they consumed isonitrogenous casein or whey mixed meals on d 12 or d 14 of experimental bed rest. Rates of phenylalanine hydroxylation were measured by primed-constant oral administration of L[2-2H2]tyrosine and L[ring-2H5]phenylalanine for 3 h in the postabsorptive state and 6 h after an isonitrogenous bolus meal containing sucrose (0.27 g/kg) and casein or whey (0.40 g/kg). Net protein synthesis in the fed state was calculated during the first 6 h postmeal as the difference between phenylalanine hydroxylation and phenylalanine content in the ingested casein or whey. In the fed state, the integrated changes in phenylalanine hydroxylation were lower (P < 0.05) after whey (−2 ± 8 μmol·kg −1·6 h −1) than after casein ingestion (34 ± 7 μmol·kg −1·6 h −1). During bed rest, net postprandial protein synthesis was greater (P < 0.05) after whey (96 ± 8 μmol phenylalanine·kg −1·6 h −1) than after casein ingestion (82 ± 7 μmol phenylalanine·kg −1·6 h −1). The rapidly digested whey protein was more efficient than the slowly digested casein in increasing postprandial net protein synthesis during short-term bed rest.

Development of double blind gluten and casein free test foods for use in an autism dietary trial

Background: Autism is a severe long‐term neurodevelopmental disorder. Families are increasingly undertaking a gluten and casein free (GFCF) diet in response to largely anecdotal reports of autistic clinical improvement. Exclusion of staple foods can place these children, with self‐imposed limited diets, at nutritional risk (Keen, 2007). There is an urgent need to investigate the efficacy of GFCF diets in an adequately powered, medium term, randomised controlled trial (Millward et al., 2007). However, double blinding to the removal of gluten and/or casein is desirable but complex to accomplish. Therefore, this study was essential preparation for a large scale study and investigated the feasibility of producing test foods to achieve double‐blinding which are transportable, easy to prepare, palatable and suitable for daily consumption by young children with autism.Methods: Heron Foods Cork, developed a range of test foods including a muffin, porridge and batter mix, lemon and almond cookies and chocolate krispie bars. The estimated average habitual intake (Gregory et al., 1995) of gluten (10 g) and/or casein (10 g) was added as outlined below: Test Food with gluten and casein added; Test Food with added casein only; Test Food with added gluten only; Test Food with no gluten or casein added. Groups were randomly labelled A–D. The foods’ GFCF status or presence of additions was confirmed by independent assay. R&amp;D and ethical approval was given for health professionals to recruit 60 children with autism (3–6 years) in Newcastle, Edinburgh and London and to randomly allocate to the above groups. Following assessment of eligibility and informed consent, families received a supply of test foods, detailed cooking instructions and behaviour and food preference questionnaires for self‐completion. Parents offered test foods for 28 days and recorded daily consumption. As this study investigated the acceptability of the test foods and not the effect of GFCF diet on autism, gluten and casein containing foods were not withdrawn from the child's diet. Telephone dietetic support was available throughout. Outcomes were measured by food consumption diaries, a test foods acceptability questionnaire and telephone interviews with a sub‐set of parents. Parents and all researchers were blind to group allocation.Results: A total of 52 children were recruited with only three families withdrawing during the 28 days due to food refusal. Results are available for the first 43 children [A – 9, B – 10, C – 13, D – 11]. Of 38 parents responding 63% stated that their children were ‘usually willing to try new foods’ [A – 86%, B – 67%, C – 42%, D – 70%]. Ninety‐five percent of the children (n = 40) [A – 89%, B – 90%, C – 100%, D – 100%] tried at least some foods over the 28 days. Muffins and chocolate krispies were most readily accepted. Porridge and batter mix were least well liked. Children in groups A and D were most likely to consume more of the foods offered. The status of the groups is not yet known but these results suggest that porridge could be removed as an option. At interview parents confirmed these findings and suggested an alternative savoury food item such as bread should be available.Discussion: Families demonstrated a high level of motivation and commitment to this study indicating their desire for dietary research in autism. The research team encountering considerable challenges in both the planning and execution of this study, but despite this, a range of test foods have been produced suitable for young children with autism.Conclusion: This is the first study to develop and test a range of double‐blind test foods for regular consumption by young children with autism. This is essential preparation for a large scale multicentered RCT of gluten and casein free diets in the management of autism.Funded by Research Autism &amp; The Children's Foundation. This work was supported by the BDA General Education Trust.References Gregory, J.R., Collins, D.L., Davies, P.S.W., Hughes, J.M. &amp; Clarke, P.C. (1995) National Diet and Nutrition Survey: children aged 1 1/2 to 4 1/2 years, volume 1: Report of the Diet and Nutrition. London: HMSO.Keen, D.V. (2007) Childhood autism, feeding problems and failure to thrive in early infancy. Seven case studies. Eur. Child. Adolesc. Psychiatry. Published online Sept 14th 2007.Millward, C., Ferriter, M., Calver, S., &amp; Connell‐Jones, G. (2007) Gluten‐ and casein‐free diets for autistic spectrum disorder. Cochrane Database Syst. Rev.4, CD003498.

Comparison of Various Methods for Endogenous Ileal Amino Acid Flow Determination in Broiler Chickens

The purpose of this study was to compare estimates of ileal endogenous amino acid (IEAA) losses determined in broiler chicks with a nitrogen-free diet (NFD), diets containing highly digestible proteins as intact casein or enzymatically hydrolyzed casein (EHC), and the regression method (RM). Male Ross 308 broiler chicks were fed a commercial starter diet from d 1 to 15 of age and the following test diets from d 15 to 21: NFD and diets containing 5, 10, or 15% casein or EHC as the sole protein source. All diets contained chromic oxide as a digestibility marker. Each diet was assigned to 6 replicate cages, with 10 birds each. On d 21, birds were euthanized to sample ileal digesta. Feeding increasing levels of EHC or casein linearly (P<0.0001) increased IEAA flow. Nonlinearity (P<0.05) was detected for Ile, Val, Glu, and Ser with EHC and for Met with casein. Compared with the NFD method, IEAA values extrapolated to zero EHC or casein intake were similar for all amino acids except Ile (200 vs. 321 mg/kg of DM intake), Val (270 vs. 341 mg/ kg of DM intake), Ala (217 vs. 262 mg/kg of DM intake), and Ser (343 vs. 577 mg/kg of DM intake), whose flows were higher with EHC (P<0.05). The present results show that IEAA values determined with the NFD, EHC, and casein diets, at different inclusion levels, were different for most amino acids and that, for all amino acids, the values obtained with NFD and RM involving feeding graded levels of casein or EHC were comparable. Thus, using IEAA values obtained with either the NFD or the RM to calculate standardized ileal amino acid digestibility coefficients will give similar values.