Compared with casein or total milk protein, digestion of milk soluble proteins is too rapid to sustain the anabolic postprandial amino acid requirement

The impact of heat-set milk protein gel textures modified by pH on circulating amino acid appearance and gastric function in healthy female adults: a randomised controlled trial

Modification of dairy proteins during processing impacts structural assemblies, influencing textural and nutritional properties of dairy products, and release and availability of amino acids during digestion. By modifying only pH, acid heat-set bovine dairy gels with divergent textural properties were developed to alter protein digestion. In vitro assay confirmed faster digestion of protein from a firm gel (pH 5.65) versus a soft gel (pH 6.55). We hypothesised that firm gel (FIRM-G; pH 5.6) would result in greater indispensable amino acid (IAA) appearance in circulation over 5 h and corresponding differences in gastric myoelectrical activity relative to soft gel (SOFT-G; pH 6.2). In a randomised, single-blind cross-over trial, healthy females (n = 20) consumed 150 g of each gel; plasma amino acid appearance was assessed over 5 hours. Iso-nitrogenous, iso-caloric gels were prepared from identical mixtures of bovine milk and whey protein concentrates; providing 17.7 g (FIRM-G) and 18.9 g (SOFT-G) of protein per serving. Secondary outcomes included gastric myoelectrical activity measured by body surface gastric mapping, glycaemic, triglyceridaemic, and subjective appetite and digestive responses. Overall plasma IAA (area under the curve) did not differ between gels. However, plasma IAA concentrations were higher, and increased more rapidly over time after SOFT-G compared with FIRM-G (1455 ± 53 versus 1350 ± 62 μmol L-1 at 30 min, p = 0.024). Similarly, total, branched-chain and dispensable amino acids were higher at 30 min with SOFT-G than FIRM-G (total: 3939 ± 97 versus 3702 ± 127 μmol L-1, p = 0.014; branched-chain: 677 ± 30 versus 619 ± 34 μmol L-1, p = 0.047; dispensable: 2334 ± 53 versus 2210 ± 76 μmol L-1, p = 0.032). All other measured parameters were similar between gels. Peak postprandial aminoacidaemia was higher and faster following ingestion of SOFT-G. Customised plasma amino acid appearance from dairy is achievable by altering gel coagulum structure using pH during processing and may have minimal influence on related postprandial responses, with implications for targeting food design for optimal health. The Clinical Trial Registry number is ACTRN12622001418763 (https://www.anzctr.org.au) registered November 7, 2022.

Minimal processed infant formula vs. conventional shows comparable protein quality and increased postprandial plasma amino acid kinetics in rats

During industrial processing, heat treatments applied to infant formulas may affect protein digestion. Recently, innovative processing routes have been developed to produce minimally heat-processed infant formula. Our objective was to compare the in vivo protein digestion kinetics and protein quality of a minimally processed (T−) and a heat-treated (T+++) infant formula. Sixty-eight male Wistar rats (21 d) were fed with either a diet containing 40 % T− (n 30) or T+++ (n 30), or a milk protein control diet (n 8) during 2 weeks. T− and T+++ rats were then sequentially euthanised 0, 1, 2, 3 or 6 h (n 6/time point) after ingestion of a meal containing their experimental diet. Control rats were euthanised 6 h after ingestion of a protein-free meal to determine nitrogen and amino acid endogenous losses. Nitrogen and amino acid true caecal digestibility was high for both T− and T+++ diets (> 90 %), but a tendency towards higher nitrogen digestibility was observed for the T− diet (96·6 ± 3·1 %) compared with the T+++ diet (91·9 ± 5·4 %, P = 0·0891). This slightly increased digestibility led to a greater increase in total amino acid concentration in plasma after ingestion of the T− diet (P = 0·0010). Comparable protein quality between the two infant formulas was found with a digestible indispensable amino acid score of 0·8. In conclusion, this study showed that minimal processing routes to produce native infant formula do not modify protein quality but tend to enhance its true nitrogen digestibility and increase postprandial plasma amino acid kinetics in rats.

True Ileal Amino Acid Digestibility and Protein Quality of 15N-Labeled Faba Bean in Healthy Humans

BACKGROUND

The recommended transition toward more plant-based diets, particularly containing legumes, requires a wider knowledge of plant protein bioavailability. Faba beans are cultivated at different latitudes and are used increasingly in human nutrition.

OBJECTIVES

We aimed to assess the nutritional quality of faba bean protein in healthy volunteers equipped with an intestinal tube to implement the ileal 15N balance method.

METHODS

Nine volunteers completed the study (7 males, 2 females, aged 33 ± 10 y, BMI: 24.7 ± 2.6 kg/m2). They were equipped with a nasoileal tube. After fasting overnight, they ingested a test meal consisting of cooked mash of dehulled faba bean seeds (20 g protein per serving of approximately 250 g) intrinsically labeled with 15N. Samples of ileal contents, plasma, and urine were collected over an 8-h postprandial period. Undigested nitrogen (N) and amino acids (AAs) were determined using isotopic MS, and subsequently, ileal digestibility and digestible indispensable amino acid score (DIAAS) were calculated. The measurement of postprandial deamination allowed calculation of the net postprandial protein utilization (NPPU).

RESULTS

The ileal N digestibility was 84.1% ± 7.7%. Postprandial deamination represented 19.2% ± 3.6% of ingested N, and the NPPU was 64.7% ± 9.7%. The ileal digestibility of individual AAs varied from 85.1% ± 13.7% for histidine to 94.2% ± 3.6% for glutamine + glutamate. The mean AA digestibility was ∼6 percentage points higher than the digestibility of N, reaching 89.8% ± 5.9%, whereas indispensable AA digestibility was 88.0% ± 7.3%. Histidine and tryptophan were the first limiting AAs [DIAAS = 0.77 (calculated by legume-specific N-to-protein conversion factor 5.4); 0.67 (by default factor 6.25)]. Sulfur AAs were limiting to a lesser extent [DIAA ratio = 0.94 (N × 5.4); 0.81 (N × 6.25)].

CONCLUSIONS

Protein ileal digestibility of cooked, dehulled faba beans in humans was moderate (<85%), but that of AAs was close to 90%. Overall protein quality was restricted by the limited histidine and tryptophan content. This trial was registered at clinicaltrials.gov as NCT05047757.

A phenylalanine-free recombinant nutritional protein for the dietary management of phenylketonuria

Phenylketonuria (PKU) is a congenital metabolic disorder that causes the systemic elevation of phenylalanine (Phe), which is neurotoxic and teratogenic. PKU is currently incurable, and management involves lifelong adherence to an unpalatable protein-restricted diet based on Phe-free amino acid mixtures. Seeking a palatable dietary alternative, we identified a Bacillus subtilis protein (GSP16O) with a well-balanced but low-Phe amino acid profile. We optimized the sequence and expressed a modified Phe-free version (GSP105) in Pseudomonas fluorescens, achieving yields of 20 g/L. The purified GSP105 protein has a neutral taste and smell, is highly soluble, and remains stable up to 80°C. Homozygous enu2 mice, a model of human PKU, were fed with diets containing either GSP105 or normal protein. The GSP105 diet led to normalization of blood Phe levels and brain monoamine neurotransmitter metabolites, and prevented maternal PKU. The GSP105 diet thus provides an alternative and efficacious dietary management strategy for PKU.

Gastric clot formation and digestion of milk proteins in static in vitro infant gastric digestion models representing different ages

Gastric digestion conditions change during infancy from newborn towards more adult digestion conditions, which can change gastric digestion kinetics. However, how these changes in gastric digestion conditions during infancy affect milk protein digestion has not been investigated. Therefore, we aimed to investigate milk protein digestion with static in vitro gastric digestion models representing one-, three- and six-month-old infants. With increasing age, gastric clots and soluble proteins were digested more extensively, which may partly be attributed to the looser gastric clot structure. Larger differences with increasing age were found for heated than unheated milk proteins, which might be caused by the presence of denatured whey proteins. Taken together, these findings show that gastric milk protein digestion increases during infancy. These in vitro gastric digestion models could be used to study how milk protein digestion changes with infant age, which may aid in developing infant formulas for different age stages.

Milk coagulation and gastric emptying in women experiencing gastrointestinal symptoms after ingestion of cow's milk

BACKGROUND

Gastrointestinal symptoms after drinking milk are often attributed to lactose intolerance or cow's milk allergy. However, some individuals without either condition still report gastrointestinal symptoms after drinking milk. This may be caused by gastric emptying (GE) rate or gastric protein coagulation. This study aimed to compare GE rate and protein coagulation after milk consumption between individuals reporting gastrointestinal symptoms and those without symptoms using a novel gastric MRI approach.

METHODS

Thirty women were included in this case-control study, of whom 15 reported gastrointestinal symptoms after drinking milk and 15 were controls. Participants underwent gastric MRI before and up to 90 min after consumption of 250 mL cow's milk. Gastric content volume and image texture of the stomach contents were used to determine GE and changes in the degree of coagulation.

KEY RESULTS

GE half-time did not differ between the groups (gastrointestinal symptom group 66 ± 18 min; control group 61 ± 14 min, p = 0.845). The gastrointestinal symptom group reported symptoms from 30 min onwards and rated pain highest at 90 min. The control group reported no symptoms. Image texture analyses showed a significantly higher percentage of coagulum and lower percentage of liquid in the group in the GI symptom group (MD 11%, 95% CI [3.9, 17], p = 0.003). In vitro data suggests that pH and proteolytic enzyme activity influence the coagulum structure.

CONCLUSIONS AND INFERENCES

Gastric milk coagulation and emptied fraction of stomach content may differ between individuals experiencing symptoms after milk consumption, possibly due to differences in pH and proteolytic enzyme activity.

Bioactive Dairy-Fermented Products and Phenolic Compounds: Together or Apart

Fermented dairy products (e.g., yogurt, kefir, and buttermilk) are significant in the dairy industry. They are less immunoreactive than the raw materials from which they are derived. The attractiveness of these products is based on their bioactivity and properties that induce immune or anti-inflammatory processes. In the search for new solutions, plant raw materials with beneficial effects have been combined to multiply their effects or obtain new properties. Polyphenols (e.g., flavonoids, phenolic acids, lignans, and stilbenes) are present in fruit and vegetables, but also in coffee, tea, or wine. They reduce the risk of chronic diseases, such as cancer, diabetes, or inflammation. Hence, it is becoming valuable to combine dairy proteins with polyphenols, of which epigallocatechin-3-gallate (EGCG) and chlorogenic acid (CGA) show a particular predisposition to bind to milk proteins (e.g., α-lactalbumin β-lactoglobulin, αs1-casein, and κ-casein). Reducing the allergenicity of milk proteins by combining them with polyphenols is an essential issue. As potential 'metabolic prebiotics', they also contribute to stimulating the growth of beneficial bacteria and inhibiting pathogenic bacteria in the human gastrointestinal tract. In silico methods, mainly docking, assess the new structures of conjugates and the consequences of the interactions that are formed between proteins and polyphenols, as well as to predict their action in the body.

Dietary Inflammatory Potential in Pediatric Diseases: A Narrative Review

Inflammatory status is one of the main drivers in the development of non-communicable diseases (NCDs). Specific unhealthy dietary patterns and the growing consumption of ultra-processed foods (UPFs) may influence the inflammation process, which negatively modulates the gut microbiota and increases the risk of NCDs. Moreover, several chronic health conditions require special long-term dietary treatment, characterized by altered ratios of the intake of nutrients or by the consumption of disease-specific foods. In this narrative review, we aimed to collect the latest evidence on the pro-inflammatory potential of dietary patterns, foods, and nutrients in children affected by multifactorial diseases but also on the dietetic approaches used as treatment for specific diseases. Considering multifactorial diet-related diseases, the triggering effect of pro-inflammatory diets has been addressed for metabolic syndrome and inflammatory bowel diseases, and the latter for adults only. Future research is required on multiple sclerosis, type 1 diabetes, and pediatric cancer, in which the role of inflammation is emerging. For diseases requiring special diets, the role of single or multiple foods, possibly associated with inflammation, was assessed, but more studies are needed. The evidence collected highlighted the need for health professionals to consider the entire dietary pattern, providing balanced and healthy diets not only to permit the metabolic control of the disease itself, but also to prevent the development of NCDs in adolescence and adulthood. Personalized nutritional approaches, in close collaboration between the hospital, country, and families, must always be promoted together with the development of new methods for the assessment of pro-inflammatory dietary habits in pediatric age and the implementation of telemedicine.

In vitro digestion of two protein-rich dairy products in the ageing gastrointestinal tract

It is still unclear if changes in protein digestibility and absorption kinetics in old age may affect the anabolic effect of high-protein foods. The objective of this study was to investigate the digestion of two high-protein (10% w/w) dairy products in vitro: a fermented dairy product formulated with a ratio of whey proteins to caseins of 80 to 20% (WBD) and a Skyr containing mainly caseins. The new static in vitro digestion model adapted to the general older adult population (≥65 years) proposed by the INFOGEST international consortium was implemented to investigate the digestion of these products and compared with the standard version of the protocol. Kinetics of proteolysis was compared between both models for each product, in the gastric and intestinal phases of digestion. Protein hydrolysis was studied by the OPA method, SDS-PAGE, and LC-MS/MS, and amino acids were quantified by HPLC. Protein hydrolysis by pepsin was slower with the older adult model than with the young adult model, and consequently, in spite of a longer gastric phase duration, the degree of proteolysis (DH) at the end of the gastric phase was lower. Two different scenarios were observed depending on the type of dairy product studied: -10 and -40% DH for Skyr and WBD, respectively. In the intestinal phase, lower concentrations of free leucine were observed in older adult conditions (approx. -10%), but no significant differences in proteolysis were observed overall between the models. Therefore, the digestion conditions used influenced significantly the rate and extent of proteolysis in the gastric phase but not in the intestinal phase.

Casein structures differently affect postprandial amino acid delivery through their intra-gastric clotting properties

We aimed to assess if casein structure affects its digestion and its subsequent amino acid delivery kinetic. Higher nitrogen levels were recovered in dialysates after in vitro digestions of sodium caseinate (SC, formed of small aggregates) compared to micellar casein (MC, native form of casein) and calcium caseinate (CC, intermediate structure). Likewise, plasma indispensable amino-acid concentration peak was higher after SC compared to MC or CC ingestion in healthy volunteers in a randomized, double blind, cross-over study. In pigs, gamma-scintigraphy using labelled meals revealed that SC was mainly localized in the proximal part of the stomach whereas MC was distributed in the whole gastric cavity. Caseins were found in both solid and liquid phases and partly hydrolyzed casein in the solid phase shortly after SC drink ingestion. These data support the concept of slow (MC) and rapid (SC) casein depending of casein structure, likely due to their intra-gastric clotting properties.

Differential effects of milk proteins on amino acid digestibility, post-prandial nitrogen utilization and intestinal peptide profiles in rats

OBJECTIVE

The aim of this study was to analyze the protein digestibility and postprandial metabolism in rats of milk protein matrices obtained by different industrial processes.

MATERIAL AND METHODS

The study was conducted on Wistar rats that consumed a meal containing different ¹⁵N-labeled milk proteins. Four milk matrices were tested: native micellar caseins (C1), caseins low in calcium (C2 low Ca²⁺), a matrix containing a ratio 63:37 of caseins and whey proteins (CW2) and whey proteins alone (W). Blood and urine were collected during the postprandial period and rats were euthanized 6 h after meal intake to collect digestive contents and organs.

RESULTS

Orocaecal digestibility values of amino acids ranged between 96.0 ± 0.2% and 96.6 ± 0.4% for C1-, C2 low Ca²⁺- and W-matrices, while this value was significantly lower for CW2 matrix (92.4 ± 0.5%). More dietary nitrogen was sequestered in the splanchnic area (intestinal mucosa and liver) as well as in plasma proteins after ingestion of W matrix, especially compared to the C1- and C2 low Ca²⁺-matrices. Peptidomic analysis showed that more milk protein-derived peptides were identified in the caecum of rats after the ingestion of the matrices containing caseins compared to W matrix.

CONCLUSION

We found that demineralization of micellar caseins did not modify its digestibility and postprandial metabolism. The low digestibility of the modified casein-to-whey ratio matrix may be ascribed to a lower accessibility of the protein to digestive enzymes due to changes in the protein structure, while the higher nitrogen splanchnic retention after ingestion of whey was probably due to the fast assimilation of its protein content. Finally, our results showed that industrial processes that modify the structure and/or composition of milk proteins influence protein digestion and utilization.

Impact of process and composition of formulas for elderly on in vitro digestion using the dynamic DIDGI® model

Due to the lower efficiency of the elderly digestion system, new formulations are needed in order to increase the bioaccessibility of macronutrients. The aim of the work was to evaluate the effect of the process of protein sources production using either liquid (F2) vs spray dried milk proteins (F1/F3) and the source of lipids (vegetable oil (F1) vs mix of vegetable oil + bovine milk cream (F2/F3)) ingredients on the macronutrient digestion of three experimental elderly formulas. The dynamic in vitro digestion model DIDGI®^, was adapted to simulate the digestive conditions of the elderly. An exhaustive review of the literature was carried out in order to simulate as closely as possible the elderly digestive parameters and constituted the starting point towards a consensus in vitro digestion model that will be proposed soon by the INFOGEST scientific network. The three experimental formulas (F1/F2/F3) differing by the composition and process applied were submitted to the DIDGI® dynamic in vitro digestion over four hours using parameters adapted to the elderly. The three formulas were compared in terms of proteolysis and lipolysis. A slight impact of the process (liquid vs spray-dried) on the degree of proteolysis at the end of digestion was observed with 50.8% for F2 compared to 56.8% for F1 and 52.9% for F3 with<5% of difference between the 3 formulas. Concerning the degree of lipolysis, the addition of bovine cream led to a lesser extent of lipolysis with 63.7 and 60.2% for F2 and F3 respectively versus 66.3% for F1 (containing only vegetable oil). Our results highlighted the beneficial input of the milk fat with a higher level of phospholipids and a lower ω6/ω3 PUFA ratio and can be a good alternative to the use of the vegetable fat in drinks for elderly people.

[Whey protein and caseinate supplementation in oncological patients undergoing elective surgery for the modification of functional capacity]

INTRODUCTION

the nutritional intervention has become a critical point to achieve the reduction of perioperative morbidity and mortality in cancer patients. There are different factors that will play a fundamental role in the evolution and prognosis of this pathology, being the state of nutrition and diet a cornerstone in these aspects.

OBJECTIVE

to evaluate the perioperative effect of whey protein isolate (WPI) and calcium caseinate (CaCNT) in cancer patients undergoing elective surgery.

METHODS

randomized controlled clinical trial with three groups: the control group (n = 15), consisting in conventional management by the oncology surgery services, and two intervention groups, one with calcium caseinate supplementation (n = 15) and another one with whey protein isolate supplementation (n = 15) for six weeks perioperatively. Handgrip strength, six-minute walk, and body composition were assessed pre and postoperatively.

RESULTS

those who were supplemented with WPI maintained their handgrip strength and showed less extracellular water (p < 0.02); also an increase in visceral mass was shown (p < 0.02). Finally, a correlation was found with variables associated with body composition and patient evolution when compared to the control group.

CONCLUSIONS

nutritional supplementation needs to be approached from the functional and metabolic point of view to identify factors that have a favorable impact, as well as the distinction between carcinoma and the type of supplementation to be implemented.

The BMI Z-Score and Protein Energy Ratio in Early- and Late-Diagnosed PKU Patients from a Single Reference Center in Mexico

The relationship between protein and energy and their appropriate proportions in hyperphenylalaninemia (HPA) or phenylketonuria (PKU) patients in terms of growth have been poorly studied, especially in those diagnosed late. We aimed to describe the protein energy ratio (P:E) and its association with body mass index (BMI) in 638 dietetic and anthropometric assessments from 54 early- or late-diagnosed HPA/PKU patients. Dietetic and anthropometric data were analyzed and classified according to BMI Z-Score and type of diagnosis, early by newborn screening (NBS) or late. Correlation between BMI Z-Score and P:E ratio was established. Percent of dietary protein from Phe-free metabolic formula was analyzed. According to the BMI Z-Score, the majority of assessments were eutrophic (69.4%). The median P:E ratio was >4 in most of the overweight assessments. Remarkably, the underweight group consumed the highest proportion of Phe-free metabolic formula (74.5%). A positive correlation between BMI Z-Score and P:E ratio was found. The highest proportion of underweight was found in the late-diagnosed patients. Our findings might be related to their nutritional history previous to the HPA/PKU treatment. Thus, complex nutritional outcome of the late-diagnosed HPA/PKU patients deserves actions to guarantee the early diagnosis, closer nutritional follow-up and alternative therapeutic approaches.

Time Courses of Gastric Volume and Content after Different Types of Casein Ingestion in Healthy Men: A Randomized Crossover Study

BACKGROUND

Few studies have evaluated differences in the curd-forming ability of casein on gastric volume and content directly after ingestion in humans.

OBJECTIVES

This study evaluated the time course of gastric volume and curd conditions in the stomach after protein ingestion.

METHODS

This was an open-labeled, randomized crossover trial. Ten healthy men [age: 33.4 ± 7.3 y; BMI (kg/m²): 21.9 ± 0.9] received 350 g of 3 isonitrogenous and isocaloric protein drinks containing 30 g micellar casein (MCN), sodium caseinate (SCN), or whey protein concentrate (WPC). The gastric antrum cross-sectional area (CSA) and curd in the stomach were measured using ultrasonography within 5 h after ingestion. The differences between test foods were tested using the MIXED model and post hoc tests using Fisher's protected least significant difference.

RESULTS

The incremental AUC of the gastric antrum CSA after MCN ingestion was 1.3-fold and 1.5-fold higher than that after the ingestion of SCN and WPC, respectively (both P < 0.05), but not different between SCN and WPC. The number of participants with curds ≥20 mm with a high echogenicity clot observed in the stomach within 5 h after MCN ingestion was significantly greater than that after the ingestion of other proteins (n = 9 for MCN, n = 2 for SCN, and n = 0 for WPC; bothP < 0.01). The regression line slopes on total plasma amino acid concentration and gastric antrum CSA were significantly different between the participants with and without curds.

CONCLUSIONS

In contrast to SCN and WPC, MCN ingestion resulted in slow kinetics of gastric antrum CSA. Differences in curd formation of casein in the stomach affect gastric emptying and plasma amino acid absorption kinetics after ingestion in healthy men. This trial was registered at University Hospital Medical Information Network Clinical Trials Registry as UMIN000038388 (https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000043746).

Milk proteins: Processing, gastric coagulation, amino acid availability and muscle protein synthesis

It is well-known that the postprandial muscle protein synthetic response to protein ingestion is regulated on various levels, including dietary protein digestion and amino acid (AA) absorption, splanchnic AA retention, the availability of dietary protein-derived AA in the circulation, delivery of AA to the muscle, uptake of AA by the muscle, and intramuscular signaling. AA availability after consumption of dairy products is primarily determined by the rate of gastric emptying of milk proteins, which is mainly linked to coagulation of milk proteins in the stomach. Caseins form gastric coagula, which make their gastric emptying and subsequent postprandial aminoacidemia notably slower than that of whey proteins. Only recently, the role of processing, food structure, preservation and matrix on coagulation herein has been getting attention. In this review we describe various processes, that affect gastric coagulation of caseins and therewith control gastric emptying, such as the conversion to caseinate, heat treatment in the presence of whey proteins, conversion to stirred yoghurt and enzymatic hydrolysis. Modulating product characteristics by processing can be very useful to steer the gastric behavior of protein, and the subsequent digestion and AA absorption and muscle anabolic response to maintain or increase muscle mass.

Isolation and characterisation of milk-derived amyloid-like protein aggregates (MAPA) from cottage cheese

Cottage cheese, extensively consumed worldwide, contains coagulated milk protein (casein), produced through boiling and acidification of milk. Casein forms amyloid or amyloid-like structures at high temperatures and low pH. Due to the similarities in the preparation of casein amyloids and cottage cheese, we hypothesized the presence of amyloid or amyloid-like protein aggregates in cottage cheese. To examine this hypothesis, cottage cheese was prepared from cow (Bos indicus) milk and isolated amyloids through a water extraction method. The isolated protein aggregates displayed typical characteristics of amyloids, such as a bathochromic shift in the wavelength of maximum absorption (λ_max) of Congo red (CR), high thioflavin T (ThT) binding, increased surface hydrophobicity, and high β-sheet structure. However, they did not show antibacterial activity and toxic properties against erythrocytes. Our study revealed that the heat-treatment and subsequent acidification during cottage cheese preparation lead to the formation of non-toxic amyloid-like aggregates.

Unraveling the Metabolic Hallmarks for the Optimization of Protein Intake in Pre-Dialysis Chronic Kidney Disease Patients

The daily amount and quality of protein that should be administered by enteral nutrition in pre-dialysis chronic kidney disease (CKD) patients is a widely studied but still controversial issue. This is due to a compromise between the protein necessary to maintain muscular proteostasis avoiding sarcopenia, and the minimal amount required to prevent uremia and the accumulation of nitrogenous toxic substances in blood because of the renal function limitations. This review underlines some intracellular and extracellular features that should be considered to reconcile those two opposite factors. On one hand, the physiological conditions and usual side effects associated with CKD, mTOR and other proteins and nutrients involved in the regulation of protein synthesis in the muscular tissue are discussed. On the other hand, the main digestive features of the most common proteins used for enteral nutrition formulation (i.e., whey, casein and soy protein) are highlighted, due to the importance of supplying key amino acids to serum and tissues to maintain their concentration above the anabolic threshold needed for active protein synthesis, thereby minimizing the catabolic pathways leading to urea formation.

Using the dual isotope method to assess cecal amino acid absorption of goat whey protein in rats, a pilot study

Measurement of ileal amino acids (AA) bioavailability is recommended to evaluate protein quality. A dual isotope tracer method, based on plasma isotopic enrichment ratios, has been proposed to determine true digestibility in humans. In a pilot study, we aimed to evaluate whether this method could be implemented in rats to determine AA bioavailability based on isotopic enrichment ratios measured in cecal digesta or plasma samples. Goat milk proteins were intrinsically labeled with ¹⁵N and ²H. Wistar rats were fed a meal containing the doubly labeled goat whey proteins and a tracer dose of ¹³C-spirulina. Blood samples were collected 0, 1 h and 3 h after meal ingestion from the tail vein. The rats were euthanized 4 h (n = 6) or 6 h (n = 6) after meal to collect plasma and intestinal contents. True orocecal protein digestibility and AA bioavailability were assessed by means of ¹⁵N and ²H enrichment in cecum content and compared with absorption indexes determined at the plasma or cecum level using isotopic ratios. Plasma kinetics of isotopic enrichment could not be completed due to the limited quantity of plasma obtained with sequential blood collection. However, the absorption indexes determined from cecal ¹⁵N or ²H/¹³C ratios gave coherent values with true orocecal AA bioavailability. This dual isotope approach with measurements of isotopic ratios in digestive content could be an interesting strategy to determine true AA bioavailability in ileal digesta of rats.

In Vivo Metabolic Responses to Different Formulations of Amino Acid Mixtures for the Treatment of Phenylketonuria (PKU)

Phenylketonuria (PKU) is a rare autosomal recessive inborn error of metabolism where the mainstay of treatment is a Phe restricted diet consisting of a combination of limited amounts of natural protein with supplementation of Phe-free or low-Phe protein substitutes and special low protein foods. Suboptimal outcomes may be related to the different absorption kinetics of free AAs, which have lower biological efficacy than natural proteins. Physiomimic Technology^TM is a technology engineered to prolong AA (AA-PT) release allowing physiological absorption and masking the odor and taste of free AAs. The aim of these studies was to assess the impact of AA-PT formulation on selected functional and metabolic parameters both in acute and long-term experimental studies. Adult rats in fasting conditions were randomized in different groups and treated by oral gavage. Acute AA-PT administration resulted in significantly lower BUN at 90 min versus baseline. Both BUN and glycemia were modulated in the same direction as intact casein protein. Long-term treatment with AA-PT significantly reduces the protein expression of the muscle degradation marker Bnip3L (−46%) while significantly increasing the proliferation of market myostatin (+58%). Animals dosed for 15 days with AA-PT had significantly stronger grip strength (+30%) versus baseline. In conclusion, the results suggest that the AA-PT formulation may have beneficial effects on both AA oxidation and catabolism with a direct impact on muscle as well as on other metabolic pathways.

Real ileal amino acid digestibility of pea protein compared to casein in healthy humans: a randomized trial

BACKGROUND

It is necessary to propose plant alternatives to animal proteins that are of good nutritional quality. Pea is a good candidate owing to its high protein content and its well-balanced amino acid (AA) profile.

OBJECTIVES

This study aimed to assess the real ileal AA and nitrogen digestibility (RIDAA and RIDN) of pea protein isolate as compared to milk casein in humans. It also aimed to evaluate their nutritional quality through calculation of the digestible indispensable amino acid score (DIAAS) and to determine the net postprandial protein utilization (NPPU).

METHODS

Fifteen healthy volunteers were included in a randomized, single-blinded, 2-arm, parallel-design trial. They were equipped with a naso-ileal tube. They ingested the test meals, which consisted of 9 successive portions of mashed potatoes containing either pea protein or casein, intrinsically labeled with nitrogen 15. Ileal content, plasma, and urine samples were collected regularly over an 8-h postprandial period.

RESULTS

The mean RIDAA values were 93.6% ± 2.9% for pea protein and 96.8% ± 1.0% for casein, with no difference between the sources (P = 0.22). Leucine, valine, lysine, and phenylalanine were significantly less digestible in pea than in casein. The RIDN values were 92.0% ± 2.7% and 94.0% ± 1.7% for pea protein and casein, respectively, and were not different (P = 0.11). The DIAAS was 1.00 for pea protein and 1.45 for casein. The NPPU was 71.6% ± 6.2% and 71.2% ± 4.9% for pea protein and casein, respectively (P = 0.88).

CONCLUSIONS

Although some AAs are less digestible in pea protein than in casein, the real ileal digestibility and the NPPU were not different. The DIAAS of 1.00 obtained for pea protein demonstrated its ability to meet all AA requirements. This study shows the potential of pea isolate as a high-quality protein. This study was registered at clinicaltrials.gov as NCT04072770.

Dairy bioactive proteins and peptides: a narrative review

Milk proteins are known for their high nutritional quality, based on their essential amino acid composition, and they exhibit a wide range of bioactivities, including satiety, antimicrobial, mineral-binding, and anti-lipidemic properties. Because of their unique water solubility, milk proteins are readily separated into casein and whey fractions, which can be further fractionated into many individual proteins, including alpha-S1- and alpha-S2-caseins, beta-casein, and kappa-casein, and the whey proteins alpha-lactalbumin, lactoferrin, beta-lactoglobulin, and glycomacropeptide. Many of these proteins have unique bioactivities. Further, over the past 30 years, peptides that are encrypted in the primary amino acid sequences of proteins and released along with amino acids during digestion are increasingly recognized as biologically active protein metabolites that may have beneficial effects on human health. This review examines the current state of the science on the contribution of dairy proteins and their unique peptides and amino acids to human health.

Protein Quality in Infant Formulas Marketed in Brazil: Assessments on Biodigestibility, Essential Amino Acid Content and Proteins of Biological Importance

Infant formulas, designed to provide similar nutritional composition and performance to human milk, are recommended when breastfeeding is not enough to provide for the nutritional needs of children under 12 months of age. In this context, the present study aimed to assess the protein quality and essential amino acid content of both starting (phase 1) and follow-up (phase 2) formulas from different manufacturers. The chemical amino acid score and protein digestibility corrected by the amino acid score were calculated. The determined protein contents in most formulas were above the maximum limit recommended by FAO and WHO guidelines and at odds with the protein contents declared in the label. All infant formulas contained lactoferrin (0.06 to 0.44 g·100 g⁻¹) and α-lactalbumin (0.02 to 1.34 g·100 g⁻¹) below recommended concentrations, whereas ĸ-casein (8.28 to 12.91 g·100 g⁻¹), α-casein (0.70 to 2.28 g·100 g⁻¹) and β-lactoglobulin (1.32 to 4.19 g·100 g⁻¹) were detected above recommended concentrations. Essential amino acid quantification indicated that threonine, leucine and phenylalanine were the most abundant amino acids found in the investigated infant formulas. In conclusion, infant formulas are still unconforming to nutritional breast milk quality and must be improved in order to follow current global health authority guidelines.

Fine-Tuning of Postprandial Responses via Feeding Frequency and Leucine Supplementation Affects Dietary Performance in Turbot (Scophthalmus maximus L.)

BACKGROUND

Feeding-induced cell signaling and metabolic responses affect utilization of dietary nutrients but are rarely taken advantage of to improve animal nutrition.

OBJECTIVES

We hypothesized that by modulating postprandial kinetics and signaling, improved dietary utilization and growth performance could be achieved in animals.

METHODS

Juvenile turbot (Scophthalmus maximus L.) with an initial mean ± SD weight of 10.1 ± 0.01 g were used. Two feeding frequencies (FFs), either 1 or 3 meals/d at a fixed 2.4% daily body weight ration, and 2 diets that were or were not supplemented with 1% crystalline leucine (Leu), were used in the 10-wk feeding trial. At the end of the trial, a 1-d force-feeding experiment was conducted using the aforementioned FF and experimental diets. Samples were collected for the analysis of postprandial kinetics of aminoacidemia, mechanistic target of rapamycin (mTOR) signaling activities, protein deposition, as well as the mRNA expression levels of key metabolic checkpoints at consecutive time points after feeding.

RESULTS

Increased FF and leucine supplementation significantly enhanced fish growth by 7.68% ± 0.53% (means ±SD) and 7.89% ± 1.25%, respectively, and protein retention by 4.01% ± 0.59% and 4.44% ± 1.63%, respectively, in feeding trial experiments. The durations of postprandial aminoacidemia and mTOR activation were extended by increased FF, whereas leucine supplementation enhanced mTOR signaling without influencing the postprandial free amino acids kinetics. Increased FF and leucine supplementation enhanced muscle protein deposition 21.6% ± 6.85% and 22.3% ± 1.52%, respectively, in a 24-h postfeeding period.

CONCLUSIONS

We provided comprehensive characterization of the postprandial kinetics of nutrient sensing and metabolic responses under different feeding regimens and leucine supplementation in turbot. Fine-tuning of postprandial kinetics could provide a new direction for better dietary utilization and animal performances in aquaculture.

Which Milk during the Second Year of Life: A Personalized Choice for a Healthy Future?

Nutrition in early life is a crucial element to provide all essential substrates for growth. Although this statement may appear obvious, several studies have shown how the intake of micro and macronutrients in toddlers differs a lot from the recommendations of scientific societies. Protein intake often exceeds the recommended amount, while the intake of iron and zinc is frequently insufficient, as well as Vitamin D. Nutritional errors in the first years of life can negatively impact the health of the child in the long term. To date, no clear evidence on which milk is suggested during the second year of life is yet to be established. In this study, we compare the nutrient profiles of cow’s milk and specific formulas as well as nutritional risks in toddlers linked to growth and childhood obesity development. The purpose of this review is to resume the latest clinical studies on toddlers fed with cow’s milk or young children formula (YCF), and the potential risks or benefits in the short and long term.

Effect of Modified Casein to Whey Protein Ratio on Dispersion Stability, Protein Quality and Body Composition in Rats

The present study was designed to investigate the effects of protein formula with different casein (C) to whey protein (W) ratios on dispersion stability, protein quality and body composition in rats. Modification of the casein to whey protein (CW) ratio affected the extent of protein aggregation, and heated CW-2:8 showed a significantly increased larger particle (>100 μm) size distribution. The largest protein aggregates were formed by whey protein self-aggregation. There were no significant differences in protein aggregation when the CW ratios changed from 10:0 to 5:5. Based on the protein quality assessment (CW-10:0, CW-8:2, CW-5:5, and CW-2:8) for four weeks, CW-10:0 showed a significantly higher feed intake (p<0.05), but the high proportion of whey protein in the diet (CW-5:5 and CW-2:8) increased the feed efficiency ratio, protein efficiency ratio, and net protein ratio compared to other groups. Similarly, CW-2:8 showed greater true digestibility compared to other groups. No significant differences in fat mass and lean mass analyzed by dual-energy x-ray absorptiometry were observed. A significant difference was found in the bone mineral density between the CW-10:0 and CW-2:8 groups (p<0.05), but no difference was observed among the other groups. Based on the results, CW-5:5 improved protein quality without causing protein instability problems in the dispersion.

Effect of age, stress and protein supply on plasma amino acids during continuous enteral nutrition; a pragmatic study in rats

BACKGROUND & AIMS

As life expectancy increases, an increasing older population may require surgery with perioperative nutritional management. While little is known about the combined effect of age and stress on amino acid metabolism during enteral nutrition, we hypothesized that blood amino acid bioavailability may be influenced not only by the characteristics of the ingested protein but also by intestinal ageing and splanchnic sequestration of amino acids. Plasma amino acid kinetics were thus evaluated in aged and adult rats receiving continuous enteral nutrition before and after standardized surgical stress.

METHODS

Sixteen 5-month-old and sixteen 21-month-old male rats were used. After a gastrostomy, the insertion of a jugular vein catheter and a one-week recovery, the animals were enterally fed with commercially available formulas containing whole milk proteins or a whey hydrolysate for 24 h before (healthy state) and 18 h after a standardized laparotomy (surgical stress). Data were analyzed by 3-factor ANOVA.

RESULTS

In all rats, enteral nutrition was associated with a marked increase in plasma alanine, threonine, lysine and proline (+50 to +150 μmol/L; p < 0.001), and a decrease in glycine (≈-80 μmol/L; p < 0.01). For most amino acids, their availability depended first on the amino acid composition of each protein and second on surgical stress. Aging was only associated with higher tyrosine and threonine availability (p < 0.001). There was only limited statistical interaction between age and surgical stress.

CONCLUSION

In rats, plasma amino acid availability during continuous enteral nutrition is determined by the nature of the protein source and the occurrence of stress. The effects of aging on plasma amino acid availability seem very limited. Commonly used formulas therefore appear to be as suitable for elderly patients as for adult patients.

Very low ileal nitrogen and amino acid digestibility of zein compared to whey protein isolate in healthy volunteers

BACKGROUND

Whey protein and zein are of nutritional interest due to their high leucine content, but little data are available on their amino acid (AA) ileal digestibility.

OBJECTIVE

This study aimed to determine ileal digestibility of whey protein isolate (WPI) and zein in healthy volunteers by use of the naso-ileal intubation method, which allows continuous collection of postprandial ileal digesta.

METHODS

Twenty-two healthy volunteers were intubated with a naso-ileal sampling device positioned at the terminal ileum level. They received a single meal of protein-free biscuits and a drink containing zein (n = 8), WPI (n = 7), or no protein (protein free, n = 7). Ileal effluents and plasma samples were collected over a 9-h postprandial period. Total nitrogen and AA contents were quantified in effluents. True ileal digestibility was calculated after correction for endogenous losses evaluated in the protein-free group.

RESULTS

True ileal nitrogen digestibility of zein was markedly lower than WPI (60.2 ± 4.5% and 91.2 ± 2.6%, respectively, P = 0.0003). True ileal digestibility of AAs ranged from 87.4 ± 2.7% for threonine to 98.4 ± 1.0% for methionine in the WPI group, and from 59.3 ± 5.6% for methionine to 69.0 ± 5.8% for arginine in the zein group. The digestible indispensable AA (IAA) score was 1.03 (histidine) for WPI and close to 0 for zein, owing to its negligible lysine content. Plasma IAA concentration significantly increased after WPI intake (P = 0.0319), whereas no effect of zein on aminoacidemia was observed, including plasma leucine, despite its high leucine content.

CONCLUSIONS

Our findings provide data on ileal digestibility of WPI and zein AAs in healthy humans and, in contrast to WPI, zein is poorly digestible. This study was registered at clinicaltrials.gov as NCT03279211.

Important determinants to take into account to optimize protein nutrition in the elderly: solutions to a complex equation

During ageing, skeletal muscle develops anabolic resistance towards the stimulation of protein synthesis induced by dietary amino acids. The stimulation of muscle protein synthesis after food intake remains insufficient, even with a protein intake recommended for healthy adults. This alteration is one of the mechanisms known to be responsible for the decrease of muscle mass and function during ageing, namely sarcopenia. Increasing dietary protein intake above the current RDA(0⋅83 g/kg/d) has been strongly suggested to overcome the anabolic resistance observed. It is also specified that the dietary protein ingested should be of good quality. A protein of good quality is a protein whose amino acid (AA) composition covers the requirement of each AA when ingested at the RDA. However, the biological value of proteins may vary among dietary sources in which AA composition could be unbalanced. In the present review, we suggest that the quality of a dietary protein is also related to several other determinants. These determinants include the speed of digestion of dietary proteins, the presence of specific AA, the food matrix in which the dietary proteins are included, the processes involved in the production of food products (milk gelation and cooking temperature), the energy supply and its nature, and the interaction between nutrients before ingestion. Particular attention is given to plant proteins for nutrition of the elderly. Finally, the timing of protein intake and its association with the desynchronized intake of energetic nutrients are discussed.

Whey Versus Casein as a Protein Source during the Weaning Period: Impact on Growth and Later Adiposity and Glucose Homeostasis in a Rat Model of Intrauterine Growth Restriction

The impact of early life protein source (whey vs. casein) on short- and long-term glucose homeostasis and adiposity is unknown and was investigated in this study. At the end of the suckling period, non-IUGR (intrauterine growth restriction) and IUGR pups were separated from dams and were randomized into four groups. From age 21-49 days, non-IUGR and IUGR pups were fed ad-libitum chow or a semi-synthetic diet (20% from protein; casein or whey) and from age 50-199 days, all groups were fed ad-libitum chow. Food intake, body composition, glucose, and insulin homeostasis were assessed. Among the chow groups, IUGR had slower growth and higher fasting glucose at age 42 days, as well as higher fasting and AUC glucose at age 192 days relative to non-IUGR. The whey IUGR group had a slower growth rate and higher fasting glycemia in early life (age 21-49 days) and higher HOMA-IR later in life (age 120-122 and 190-192 days) relative to casein IUGR. This study shows the potential advantage of casein relative to whey during weaning on short term energy intake, growth, and glucose homeostasis in an IUGR model and reveals, for the first time, its long term impact on insulin sensitivity, which may have implications for later metabolic health, particularly in small-for-gestational-age populations at risk of type 2 diabetes.

In Vitro Assessment of the Impact of Industrial Processes on the Gastrointestinal Digestion of Milk Protein Matrices Using the INFOGEST Protocol

The goal of this study was to determine the impact of industrial processes on the digestion of six milk protein matrices using the harmonized INFOGEST in vitro static digestion protocol. First, this method was optimized to simple protein matrices using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and size exclusion chromatography (SEC) to compare the intestinal protein hydrolysis obtained with increasing quantities of pancreatin. Similar results were achieved with the originally required pancreatin amount (trypsin activity of 100 U.mL⁻¹) and with a quantity of pancreatin equivalent to a trypsin activity of 27.3 U.mL⁻¹, which was thus used to perform the in vitro digestion of the milk matrices. Molecular weight profiles, peptide heterogeneity from LC-MS/MS data, calcium, free amino acid, and peptide concentrations were determined in the gastric and intestinal phases to compare the milk protein digests. Results showed that the industrial process affected not only the protein distribution of the matrices but also most likely the protein structures. Indeed, differences arose in terms of peptide populations generated when the caseins were reticulated or when their calcium concentrations were reduced.

The Impact of the Use of Glycomacropeptide on Satiety and Dietary Intake in Phenylketonuria

Protein is the most satiating macronutrient, increasing secretion of gastrointestinal hormones and diet induced thermogenesis. In phenylketonuria (PKU), natural protein is restricted with approximately 80% of intake supplied by a synthetic protein source, which may alter satiety response. Casein glycomacropeptide (CGMP-AA), a carbohydrate containing peptide and alternative protein substitute to amino acids (AA), may enhance satiety mediated by its bioactive properties. Aim: In a three-year longitudinal; prospective study, the effect of AA and two different amounts of CGMP-AA (CGMP-AA only (CGMP100) and a combination of CGMP-AA and AA (CGMP50) on satiety, weight and body mass index (BMI) were compared. Methods: 48 children with PKU completed the study. Median ages of children were: CGMP100; (n = 13), 9.2 years; CGMP50; (n = 16), 7.3 years; and AA (n = 19), 11.1 years. Semi-quantitative dietary assessments and anthropometry (weight, height and BMI) were measured every three months. Results: The macronutrient contribution to total energy intake from protein, carbohydrate and fat was similar across the groups. Adjusting for age and gender, no differences in energy intake, weight, BMI, incidence of overweight or obesity was apparent between the groups. Conclusion: In this three-year longitudinal study, there was no indication to support a relationship between CGMP and satiety, as evidenced by decreased energy intake, thereby preventing overweight or obesity. Satiety is a complex multi-system process that is not fully understood.

An Observational Study Evaluating the Introduction of a Prolonged-Release Protein Substitute to the Dietary Management of Children with Phenylketonuria

Dietary restriction of phenylalanine combined with a protein substitute prevents intellectual disability in patients with phenylketonuria (PKU). However, current protein substitutes are associated with low adherence owing to unpalatability and burdensome administration regimens. This prospective, observational acceptability study in children with PKU assessed the use of a prolonged-release protein substitute designed with an ethyl cellulose and arginate coating masking the bitter taste, smell and reducing the osmolarity of free amino acids. The study product was mixed with the subject’s food or drink and replaced ≥1 dose per day of the subject’s usual protein substitute for 7 days. Seven of 13 subjects were able to take their prescribed dose over the 7 day period. Most subjects mixed the test protein substitute with food or fruit juice. Reduced blood phenylalanine levels (n = 5) and improved phenylalanine/tyrosine ratio (n = 4) were recorded from baseline to Day 7, respectively. Four subjects reported fewer gastrointestinal symptoms compared to baseline. There were no cases of diarrhoea, constipation, bloating, nausea or vomiting. No adverse reactions were reported. In conclusion, the novel prolonged-release protein substitute was taken in a different way to a typical protein substitute and enabled satisfactory blood phenylalanine control. The study product was well tolerated; subjects experienced fewer gastrointestinal symptoms than with their previous treatment. Although the results of this pilot study provide reassuring data, longer-term studies evaluating adherence and blood phenylalanine control are necessary.

Amino Acid Plasma Profiles from a Prolonged-Release Protein Substitute for Phenylketonuria: A Randomized, Single-Dose, Four-Way Crossover Trial in Healthy Volunteers

Several disorders of amino acid (AA) metabolism are treated with a protein-restricted diet supplemented with specific AA mixtures. Delivery kinetics impacts AA absorption and plasma concentration profiles. We assessed plasma profiles after ingestion of an AA mixture engineered to prolong AA absorption with Physiomimic Technology^TM (Test) in a randomized, single-dose, four-way crossover trial in healthy volunteers (Trial Registration: ISRCTN11016729). In a two-step hypothesis, the primary endpoints were (i) significant reduction in peak plasma concentrations (C_max) of essential amino acids (EAAs) while (ii) maintaining EAA bioavailability (AUC_{0-300 min}) compared to a free AA mixture (Reference). Secondary endpoints included effects on plasma profiles of other AA groups and effects on several metabolic markers. Thirty subjects completed the study. Both co-primary endpoints were met: C_max for EAAs was 27% lower with the Test product compared to the Reference product (ratio, 0.726, p < 0.0001); overall plasma EAA levels from the two AA mixtures was within the pre-specified bioequivalence range (AUC_0-300min ratio, 0.890 (95% CI: 0.865, 0.915)). These findings were supported by the results of secondary endpoints. Prolongation of AA absorption was associated with modulation of several metabolic markers. It will be important to understand whether this can improve the long-term management of disorders of AA metabolism.

Dairy structures and physiological responses: a matter of gastric digestion

Digestion and health properties of food do not solely rely on the sum of nutrients but are also influenced by food structure. Dairy products present an array of structures due to differences in the origin of milk components and the changes induced by processing. Some dairy structures have been observed to induce specific effects on digestion rates and physiological responses. However, the underlying mechanisms are not fully understood. Gastric digestion plays a key role in controlling digestion kinetics. The main objective of this review is to expose the relevance of gastric phase as the link between dairy structures and physiological responses. The focus is on human and animal studies, and physiological relevant in vitro digestion models. Data collected showed that the structure of dairy products have a profound impact on rate of nutrient bioavailability, absorption and physiological responses, suggesting gastric digestion as the main driver. Control of gastric digestion can be a tool for delivering specific rates of nutrient digestion. Therefore, the design of food structure targeting specific gastric behavior could be of great interest for particular population needs e.g. rapid nutrient digestion will benefit elderly, and slow nutrient digestion could help to enhance satiety.

Post Meal Energy Boluses Do Not Increase the Duration of Muscle Protein Synthesis Stimulation in Two Anabolic Resistant Situations

BACKGROUND

When given in the long term, whey proteins alone do not appear to be an optimal nutritional strategy to prevent or slow down muscle wasting during aging or catabolic states. It has been hypothesized that the digestion of whey may be too rapid during a catabolic situation to sustain the anabolic postprandial amino acid requirement necessary to elicit an optimal anabolic response. Interestingly, it has been shown recently that the duration of the postprandial stimulation of muscle protein synthesis in healthy conditions can be prolonged by the supplementary ingestion of a desynchronized carbohydrate load after food intake. We verified this hypothesis in the present study in two different cases of muscle wasting associated with anabolic resistance, i.e., glucocorticoid treatment and aging.

METHODS

Multi-catheterized minipigs were treated or not with glucocorticoids for 8 days. Muscle protein synthesis was measured sequentially over time after the infusion of a 13C phenylalanine tracer using the arterio-venous method before and after whey protein meal ingestion. The energy bolus was given 150 min after the meal. For the aging study, aged rats were fed the whey meal and muscle protein synthesis was measured sequentially over time with the flooding dose method using 13C Valine. The energy bolus was given 210 min after the meal.

RESULTS

Glucocorticoid treatment resulted in a decrease in the duration of the stimulation of muscle protein synthesis. The energy bolus given after food intake was unable to prolong this stimulation despite a simultaneous increase of insulin and glucose following its absorption. In old rats, a similar observation was made with no effect of the energy bolus on the duration of the muscle anabolic response following whey protein meal intake.

CONCLUSIONS

Despite very promising observations in healthy situations, the strategy aimed at increasing muscle protein synthesis stimulation by giving an energy bolus during the postprandial period remained inefficient in our two anabolic resistance models.

Acute effect of an amino acid mixture in the rat glycemic profile

Amino acid mixtures (AAM) are protein substitutes used for phenylketonuria treatment, but their metabolic effects have not been well characterized. The objective of this study was to compare the acute glycemic response to free amino acids (free AA) from AAM with the response to intact protein (iProtein). Male Wistar rats (n = 14) were administered by gavage a bolus of free AA (n = 7) or iProtein as albumin (n = 7) containing equivalent amounts of nitrogen. Blood glucose and insulin levels were measured at baseline and 15, 30, 60 and 120 minutes later, when gut GLP-1 content and pancreatic insulin, GLP-1 receptor and Ki67 expression were quantified at 120 minutes time point. After AAM, glucose area under the curve (free AA vs iProtein; P < 0.01), serum insulin levels at 120 minutes (free AA vs iProtein; P < 0.05), colon GLP-1 content (free AA vs iProtein; P < 0.01), pancreatic GLP-1 receptor (free AA vs iProtein; P < 0.01) and insulin expression (free AA vs iProtein; p < 0.01) were significantly lower as compared with iProtein. AAM increased Ki67 expression in pancreatic islets (free AA vs iProtein; P < 0.05). In conclusion, this study demonstrated that acute response to AAM differs from iProtein and is characterized by a lower glucose excursion, along with a decrease in gut GLP-1 and pancreatic GLP-1 receptor and insulin. This data suggests the modulation of glycemia by free AA is mediated by the incretin axis.

The Effect of Glycomacropeptide versus Amino Acids on Phenylalanine and Tyrosine Variability over 24 Hours in Children with PKU: A Randomized Controlled Trial

Introduction: In phenylketonuria (PKU), evidence suggests that casein glycomacropeptide supplemented with rate-limiting amino acids (CGMP-AA) is associated with better protein utilisation and less blood phenylalanine (Phe) variability. Aim: To study the impact of CGMP-AA on blood Phe variability using 3 different dietary regimens in children with PKU. Methods: This was a 6-week randomised controlled cross-over study comparing CGMP-AA vs. Phe-free l-amino acids (l-AA) assessing blood Phe and tyrosine (Tyr) variability over 24 h in 19 children (7 boys) with PKU, with a median age of 10 years (6–16). Subjects were randomised to 3 dietary regimens: (1) R1, CGMP-AA and usual dietary Phe (CGMP + Phe); (2) R2, CGMP-AA − Phe content of CGMP-AA from usual diet (CGMP − Phe); and (3) R3, l-AA and usual dietary Phe. Each regimen was administered for 14 days. Over the last 48 h on days 13 and 14, blood spots were collected every 4 h at 08 h, 12 h, 16 h, 20 h, 24 h, and 04 h. Isocaloric intake and the same meal plan and protein substitute dosage at standardised times were maintained when blood spots were collected. Results: Eighteen children completed the study. Median Phe concentrations over 24 h for each group were (range) R1, 290 (30–580), R2, 220 (10–670), R3, 165 (10–640) μmol/L. R1 vs. R2 and R1 vs. R3 p < 0.0001; R2 vs. R3 p = 0.0009. There was a significant difference in median Phe at each time point between R1 vs. R2, p = 0.0027 and R1 vs. R3, p < 0.0001, but not between any time points for R2 vs. R3. Tyr was significantly higher in both R1 and R2 [70 (20–240 μmol/L] compared to R3 [60 (10–200) μmol/L]. In children < 12 years, blood Phe remained in the target range (120–360 μmol/L), over 24 h, for 75% of the time in R1, 72% in R2 and 64% in R3; for children aged ≥ 12 years, blood Phe was in target range (120–600 μmol/L) in R1 and R2 for 100% of the time, but 64% in R3. Conclusions: The residual Phe in CGMP-AA increased blood Phe concentration in children. CGMP-AA appears to give less blood Phe variability compared to l-AA, but this effect may be masked by the increased blood Phe concentrations associated with its Phe contribution. Reducing dietary Phe intake to compensate for CGMP-AA Phe content may help.

Influence of milk processing temperature on growth performance, nitrogen retention, and hindgut's inflammatory status and bacterial populations in a calf model

This research communication describes a study aimed at evaluating the effects of heat treatment of milk on growth performance, N retention, and hindgut's inflammatory status and bacterial populations using young dairy calves as a model. Twenty-one Holstein calves were randomly allocated to one of three treatments: raw milk (RM), pasteurised milk (PAST), or UHT milk (UHT). Calves were submitted to a N balance study, and a biopsy from the distal colon and a faecal sample were obtained from 5 animals per treatment to determine expression of several genes and potential changes in the hindgut's bacterial population. Milk furosine content was 33-fold greater in UHT than in RM and PAST milks. Calves receiving RM grew more than those fed UHT, and urinary N excretion was greatest in calves fed UHT. Quantification of Lactobacillus was lower in calves consuming PAST or UHT, and Gram negative bacteria were greater in UHT than in PAST calves. The expression of IL-8 in the hindgut's mucosa was lowest and that of IL-10 tended to be lowest in RM calves, and expression of claudin-4 tended to be greatest in UHT calves. In conclusion, the nutritional value of UHT-treated milk may be hampered because it compromises growth and increases N excretion in young calves and may have deleterious effects on the gut's bacterial population and inflammation status.

A critical evaluation of the anabolic response after bolus or continuous feeding in COPD and healthy older adults

After bolus and continuous enteral feeding of the same protein, different digestion and absorption kinetics and anabolic responses are observed. Establishing which mode of feeding has the highest anabolic potential in patients with chronic obstructive pulmonary disease (COPD) may aid in the prevention of muscle wasting, but an important confounding factor is the duration of assessments after bolus feeding. We hypothesized that the anabolic response to bolus and continuous feeding in COPD patients is comparable when methodological issues are addressed. Twenty-one older adults (12 patients with stage II-IV COPD and 9 healthy controls) were studied after intake of a fast-absorbing hydrolyzed casein protein-carbohydrate mixture either as a single bolus or as small sips (crossover design). Whole body protein synthesis (PS), breakdown (PB), net PS (PS - PB) protein efficiency (netPSPE), net protein balance (phenylalanine (PHE) intake - PHE hydroxylation) protein efficiency (netBalPE), and splanchnic PHE extraction (SPE_PHE) were assessed using stable isotope tracer methodology. Bolus feeding assessments were done at 90, 95, and 99% of the calculated duration of the anabolic response. At 99%, netBalPE was higher for sip feeding than bolus feeding in both groups (P<0.0001). Nevertheless, bolus feeding was associated with a lower SPE_PHE (P<0.0001) and higher netPSPE (P<0.0001). At 90% compared with 99%, PS and netBalPE after bolus feeding was significantly overestimated. In conclusion, several factors complicate a comparison of the anabolic capacity of bolus and continuous feeding in acute studies, including the critical role of SPE calculation and assumptions, and the duration of postprandial assessments after bolus feeding.