Abstract
Protein-rich supplements are used widely to prevent and manage undernutrition in older people. We have previously shown that healthy older, compared to younger, adults have less suppression of energy intake by whey protein—although the effects of age on appetite-related gut hormones are largely unknown. The aim of this study was to determine and compare the acute effects of whey protein loads on blood glucose and plasma gut hormone concentrations in older and younger adults. Sixteen healthy older (eight men, eight women; mean ± SEM: age: 72 ± 1 years; body mass index: 25 ± 1 kg/m2) and 16 younger (eight men, eight women; 24 ± 1 years; 23 ± 0.4 kg/m2) adults were studied on three occasions in which they ingested 30 g (120 kcal) or 70 g (280 kcal) whey protein, or a flavored-water control drink (~2 kcal). At regular intervals over 180 min, blood glucose and plasma insulin, glucagon, ghrelin, cholecystokinin (CCK), gastric inhibitory peptide (GIP), and glucagon-like peptide-1 (GLP-1) concentrations were measured. Plasma ghrelin was dose-dependently suppressed and insulin, glucagon, CCK, GIP, and GLP-1 concentrations were dose-dependently increased by the whey protein ingestion, while blood glucose concentrations were comparable during all study days. The stimulation of plasma CCK and GIP concentrations was greater in older than younger adults. In conclusion, orally ingested whey protein resulted in load-dependent gut hormone responses, which were greater for plasma CCK and GIP in older compared to younger adults.
Highlights
Despite the well-recognized major adverse impact of nutritional impairment on the health of the elderly, including ageing-related muscle loss [1], and related increase in the use of high-energy drinks, usually rich in whey protein, few nutritional studies have involved older people
Baseline concentrations after an overnight fast of blood glucose, plasma glucagon (64 ± 4 and 68 ± 4 pg/mL), ghrelin (1438 ± 156 and 1507 ± 207 pg/mL), and gastric inhibitory polypeptide (GIP) (13 ± 2 vs. 16 ± 2 pmol/L) were comparable between age groups (p > 0.05), while insulin was lower and CCK (4.8 ± 0.6 vs. 3.3 ± 0.4 pmol/L, p = 0.033) and glucagon-like peptide-1 (GLP-1) (32 ± 4 vs. 22 ± 2 pmol/L, p = 0.041) were higher in healthy older compared to younger adults
Nadir glucose was lower (p = 0.005), and peak glucagon (p = 0.001) and GLP-1 (p = 0.001) were higher after 70 g compared to 30 g whey protein ingestion
Summary
Despite the well-recognized major adverse impact of nutritional impairment on the health of the elderly, including ageing-related muscle loss [1], and related increase in the use of high-energy drinks, usually rich in whey protein, few nutritional studies have involved older people. The incretin hormones gastric inhibitory polypeptide (GIP) and GLP-1 play major roles in the control of plasma insulin, glucagon, and blood glucose concentrations in response to nutrient ingestion [4]. Others, have reported that age affects gut hormone responses; healthy older, compared to younger, adults had higher CCK concentrations after overnight fasting, after mixed nutrient intake [5,6], and during intraduodenal glucose and lipid infusions [7], in addition to higher insulin in response to intraduodenal glucose infusion [8], higher GIP after glucose ingestion [9,10], and higher GLP-1 after an overnight fast [9,11,12]
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