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Acute Effects of Substitution, and Addition, of Carbohydrates and Fat to Protein on Gastric Emptying, Blood Glucose, Gut Hormones, Appetite, and Energy Intake

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      Abstract

      Whey protein, when ingested on its own, load-dependently slows gastric emptying and stimulates gut hormone concentrations in healthy young men. The aim of this study was to determine the effects of substitution, and addition, of carbohydrate (dextrose) and fat (olive oil) to whey protein. In randomized, double-blind order, 13 healthy young men (age: 23 ± 1 years, body mass index: 24 ± 1 kg/m2) ingested a control drink (450 mL; ~2 kcal/‘control’) or iso-volumetric drinks containing protein/carbohydrate/fat: (i) 14 g/28 g/12.4 g (280 kcal/‘M280′), (ii) 70 g/28 g/12.4 g (504kcal/‘M504′), and (iii) 70 g/0 g/0 g (280 kcal/‘P280′), on 4 separate study days. Gastric emptying (n = 11, 3D-ultrasonography), blood glucose, plasma insulin, ghrelin, cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) concentrations (0–180 min), appetite (visual analogue scales), and ad-libitum buffet-meal energy intake (180–210 min) were determined. Substitution of protein with carbohydrate and fat was associated with faster gastric emptying (lower 50% emptying time (T50)), reduced suppression of ghrelin, and stimulation of GLP-1 (all P < 0.001); while the addition of carbohydrate and fat to protein did not affect gastric emptying or gut hormone responses significantly. Total energy intake (i.e., drink plus meal) was greater after all caloric drinks than control (P < 0.001). In conclusion, substitution of whey protein with dextrose and olive oil accelerated gastric emptying. Higher protein content of a mixed macronutrient drink increased gut hormone and insulin responses.

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      Glucagon-like peptide-1 (7-36)amide and glucose-dependent insulinotropic polypeptide secretion in response to nutrient ingestion in man: acute post-prandial and 24-h secretion patterns.

      The acute effects of different macronutrients on the secretion of glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) and glucose-dependent insulinotropic polypeptide (GIP) were compared in healthy human subjects. Circulating levels of the two hormones were measured over a 24-h period during which subjects consumed a mixed diet. In the first study, eight subjects consumed three equicaloric (375 kcal) test meals of carbohydrate, fat and protein. Small increases in plasma GLP-1(7-36) amide were found after all meals. Levels reached a maximum 30 min after the carbohydrate and 150 min after the fat load. Ingestion of both carbohydrate and fat induced substantial rises in GIP secretion, but the protein meal had no effect. In a second study, eight subjects consumed 75 g glucose or the equivalent portion of complex carbohydrate as boiled brown rice or barley. Plasma GIP, insulin and glucose levels increased after all three meals, the largest increase being observed following glucose and the smallest following the barley meal. Plasma GLP-1(7-36)amide levels rose only following the glucose meal. In the 24-h study, plasma GLP-1(7-36)amide and GIP concentrations were increased following every meal and remained elevated throughout the day, only falling to fasting levels at night. The increases in circulating GLP-1(7-36)amide and GIP levels following carbohydrate or a mixed meal are consistent with their role as incretins. The more sustained rises observed in the daytime during the 24-h study are consistent with an anabolic role in lipid metabolism.
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        Calculating correlation coefficients with repeated observations: Part 1--Correlation within subjects.

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          Glucagon-like peptide 1 inhibition of gastric emptying outweighs its insulinotropic effects in healthy humans.

          Glucagon-like peptide 1 (GLP-1) has been shown to inhibit gastric emptying of liquid meals in type 2 diabetic patients. It was the aim of the present study to compare the action of physiological and pharmacological doses of intravenous GLP-1-(7-36) amide and GLP-1-(7-37) on gastric emptying in normal volunteers. Nine healthy subjects participated (26 +/- 3 yr; body mass index 22.9 +/- 1.6 kg/m2; hemoglobin A1C 5.0 +/- 0.2%) in five experiments on separate occasions after an overnight fast. A nasogastric tube was positioned for the determination of gastric volume by use of a dye-dilution technique (phenol red). GLP-1-(7-36) amide (0.4, 0.8, or 1.2 pmol.kg-1.min-1), GLP-1-(7-37) (1.2 pmol.kg-1.min-1), or placebo was infused intravenously from -30 to 240 min. A liquid meal (50 g sucrose, 8% amino acids, 440 ml, 327 kcal) was administered at 0 min. Glucose, insulin, and C-peptide were measured over 240 min. Gastric emptying was dose dependently slowed by GLP-1-(7-36) amide (P < 0.0001). Effects of GLP-1-(7-37) at 1.2 pmol.kg-1.min-1 were virtually identical. GLP.1 dose dependently stimulated fasting insulin secretion (-30 to 0 min) and slightly reduced glucose concentrations. After the meal (0-240 min), integrated incremental glucose (P < 0.0001) and insulin responses (P = 0.01) were reduced (dose dependently) rather than enhanced. In conclusion, 1) GLP-1-(7-36) amide or -(7-37) inhibits gastric emptying also in normal subjects, 2) physiological doses (0.4 pmol.kg-1.min-1) still have a significant effect, 3) despite the known insulinotropic actions of GLP-1-(7-36) amide and -(7-37), the net effect of administering GLP-1 with a meal is no change or a reduction in meal-related insulin responses. These findings suggest a primarily inhibitory function for GLP-1 (ileal brake mechanisms).
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            Author and article information

            Affiliations
            [1 ]Adelaide Medical School and National Health and Medical Research Council of Australia (NHMRC) Centre of Research Excellence (CRE) in Translating Nutritional Science to Good Health, The University of Adelaide, Adelaide 5000, Australia; caroline.giezenaar@ 123456adelaide.edu.au (C.G.); kylie.lange@ 123456adelaide.edu.au (K.L.); karen.jones@ 123456adelaide.edu.au (K.L.J.); michael.horowitz@ 123456adelaide.edu.au (M.H.); ian.chapman@ 123456adelaide.edu.au (I.C.)
            [2 ]Department of Medicine, Haukeland University Hospital, 5021 Bergen, Norway; trygve.hausken@ 123456helse-bergen.no
            [3 ]Royal Adelaide Hospital, Adelaide 5000, Australia
            Author notes
            [* ]Correspondence: stijn.soenen@ 123456adelaide.edu.au ; Tel.: +61-8-8313-3638
            Journal
            Nutrients
            Nutrients
            nutrients
            Nutrients
            MDPI
            2072-6643
            07 October 2018
            October 2018
            : 10
            : 10
            30301241
            6213197
            10.3390/nu10101451
            nutrients-10-01451
            © 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 ( http://creativecommons.org/licenses/by/4.0/).

            Categories
            Article

            Nutrition & Dietetics

            whey protein, gastric emptying, gut hormones, blood glucose, appetite

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