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Dose-Dependent Effects of Randomized Intraduodenal Whey-Protein Loads on Glucose, Gut Hormone, and Amino Acid Concentrations in Healthy Older and Younger Men

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      Protein-rich supplements are used widely for the prevention and management of malnutrition in older people. We have reported that healthy older, compared to younger, adults have less suppression of energy intake by whey-protein—effects on appetite-related hormones are unknown. The objective was to determine the effects of intraduodenally administered whey-protein on glucose, gut hormone, and amino acid concentrations, and their relation to subsequent ad libitum energy intake at a buffet meal, in healthy older and younger men. Hydrolyzed whey-protein (30 kcal, 90 kcal, and 180 kcal) and a saline control (~0 kcal) were infused intraduodenally for 60 min in 10 younger (19–29 years, 73 ± 2 kg, 22 ± 1 kg/m2) and 10 older (68–81 years, 79 ± 2 kg, 26 ± 1 kg/m2) healthy men in a randomized, double-blind fashion. Plasma insulin, glucagon, gastric inhibitory peptide (GIP), glucagon-like peptide-1 (GLP-1), peptide tyrosine-tyrosine (PYY), and amino acid concentrations, but not blood glucose, increased, while ghrelin decreased during the whey-protein infusions. Plasma GIP concentrations were greater in older than younger men. Energy intake correlated positively with plasma ghrelin and negatively with insulin, glucagon, GIP, GLP-1, PYY, and amino acids concentrations (p < 0.05). In conclusion, intraduodenal whey-protein infusions resulted in increased GIP and comparable ghrelin, insulin, glucagon, GIP, GLP-1, PYY, and amino acid responses in healthy older and younger men, which correlated to subsequent energy intake.

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      Most cited references 54

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      The steady-state basal plasma glucose and insulin concentrations are determined by their interaction in a feedback loop. A computer-solved model has been used to predict the homeostatic concentrations which arise from varying degrees beta-cell deficiency and insulin resistance. Comparison of a patient's fasting values with the model's predictions allows a quantitative assessment of the contributions of insulin resistance and deficient beta-cell function to the fasting hyperglycaemia (homeostasis model assessment, HOMA). The accuracy and precision of the estimate have been determined by comparison with independent measures of insulin resistance and beta-cell function using hyperglycaemic and euglycaemic clamps and an intravenous glucose tolerance test. The estimate of insulin resistance obtained by homeostasis model assessment correlated with estimates obtained by use of the euglycaemic clamp (Rs = 0.88, p less than 0.0001), the fasting insulin concentration (Rs = 0.81, p less than 0.0001), and the hyperglycaemic clamp, (Rs = 0.69, p less than 0.01). There was no correlation with any aspect of insulin-receptor binding. The estimate of deficient beta-cell function obtained by homeostasis model assessment correlated with that derived using the hyperglycaemic clamp (Rs = 0.61, p less than 0.01) and with the estimate from the intravenous glucose tolerance test (Rs = 0.64, p less than 0.05). The low precision of the estimates from the model (coefficients of variation: 31% for insulin resistance and 32% for beta-cell deficit) limits its use, but the correlation of the model's estimates with patient data accords with the hypothesis that basal glucose and insulin interactions are largely determined by a simple feed back loop.
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        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 as NCT00557388.
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            Author and article information

            [1 ]Discipline of Medicine and National Health and Medical Research Council of Australia (NHMRC) Centre of Research Excellence in Translating Nutritional Science to Good Health, Adelaide Medical School, Adelaide 5000, Australia; caroline.giezenaar@ (C.G.); natalie.luscombe-marsh@ (N.D.L.-M.); amy.hutchsison@ (A.T.H.); scott.standfield@ (S.S.); christine.feinle@ (C.F.-B.); michael.horowitz@ (M.H.); ian.chapman@ (I.C.)
            [2 ]Commonwealth Scientific and Industrial Research Organisation (CSIRO), Food and Nutrition, Adelaide 5000, Australia
            Author notes
            [* ]Correspondence: stijn.soenen@ ; Tel.: +61-8-8313-3638
            12 January 2018
            January 2018
            : 10
            : 1
            © 2018 by the authors.

            Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (


            Nutrition & Dietetics

            whey protein, ageing, gut hormones


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