Responses in gut hormones and hunger to diets with either high protein or a mixture of protein plus free amino acids supplied under weight-loss conditions

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High-protein diets are an effective means for weight loss (WL), but the mechanisms are unclear. One hypothesis relates to the release of gut hormones by either protein or amino acids (AA). The present study involved overweight and obese male volunteers (n 18, mean BMI 36·8 kg/m2) who consumed a maintenance diet for 7 d followed by fully randomised 10 d treatments with three iso-energetic WL diets, i.e. with either normal protein (NP, 15 % of energy) or high protein (HP, 30 %) or with a combination of protein and free AA, each 15 % of energy (NPAA). Psychometric ratings of appetite were recorded hourly. On day 10, plasma samples were taken at 30 min intervals over two consecutive 5 h periods (covering post-breakfast and post-lunch) and analysed for AA, glucose and hormones (insulin, total glucose-dependent insulinotropic peptide, active ghrelin and total peptide YY (PYY)) plus leucine kinetics (first 5 h only). Composite hunger was 16 % lower for the HP diet than for the NP diet (P< 0·01) in the 5 h period after both meals. Plasma essential AA concentrations were greatest within 60 min of each meal for the NPAA diet, but remained elevated for 3-5 h after the HP diet. The three WL diets showed no difference for either fasting concentrations or the postprandial net incremental AUC (net AUCi) for insulin, ghrelin or PYY. No strong correlations were observed between composite hunger scores and net AUCi for either AA or gut peptides. Regulation of hunger may involve subtle interactions, and a range of signals may need to be integrated to produce the overall response.

Original languageEnglish
Pages (from-to)1254-1270
Number of pages17
JournalBritish Journal of Nutrition
Issue number8
Early online date26 Mar 2015
Publication statusPublished - Apr 2015

Bibliographical note

The authors gratefully acknowledge Jean Bryce, Nina Lamza
and Karen Taylor at the Human Nutrition Unit at RINH for
their support for meal preparation. The authors also acknowledge
Vivien Buchan (multiplex hormone assays), A. Graham
Calder and Susan Anderson (both stable isotope analyses)
for vital analytical inputs.
The present study was funded as part of the core grant from
the Rural and Environment Science and Analytical Services Division (RESAS) of the Scottish Government to the Rowett Institute of Nutrition and Health, University of Aberdeen. The authors’ contributions are as follows: G. E. L., A. M. J. and G. H. were responsible for the study concept and design; A. M. J., G. E. L., D. M. B. and C. F. were responsible for the data collection and collation; G. E. L., G. W. H. and
G. H. were responsible for the data analysis and statistical matters; G. E. L., A. M. J., G.W. H. and G. H. were responsible for the first draft and critical revision of the manuscript for important intellectual content


  • high-protein diets
  • weight loss
  • amino acids
  • composite hunger
  • leucine kinetics
  • gut hormones


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