Research

Soy isoflavones increase preprandial peptide YY (PYY), but have no effect on ghrelin and body weight in healthy postmenopausal women

Martin O Weickert^1,2* , Manja Reimann^1,3* , Bärbel Otto⁴ , Wendy L Hall⁵ , Katherina Vafeiadou⁵ , Jesper Hallund⁶ , Marika Ferrari⁷ , Duncan Talbot⁸ , Francesco Branca⁷ , Susanne Bügel⁶ , Christine M Williams⁵ , Hans-Joachim Zunft¹ and Corinna Koebnick^1,9

¹  German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany

²  Dept. of Endocrinology, Diabetes and Nutrition, Charité-University-Medicine, Berlin, Germany

³  School for Physiology, Nutrition and Consumer Sciences, North-West University Potchefstroom-Campus, Potchefstroom, South Africa

⁴  Medical Dept., University Hospital Innenstadt, Munich, Germany

⁵  School of Food Biosciences, University of Reading, Reading, UK

⁶  The Royal Veterinary & Agricultural University, Research Dept. of Human Nutrition, Centre for Advanced Food Studies, Frederiksberg, Denmark

⁷  Istituto Nazionale di Ricerca per gli Alimenti e la Nutrizione, Rome, Italy

⁸  Unilever Corporate Research, Colworth House, Sharnbrook, Bedfordshire, UK

⁹  Dept. of Preventive Medicine, University of Southern California, Los Angeles, USA

author email corresponding author email* Contributed equally

Journal of Negative Results in BioMedicine 2006, 5:11doi:10.1186/1477-5751-5-11

Published:	14 August 2006

Abstract

Background

Soy isoflavones show structural and functional similarities to estradiol. Available data indicate that estradiol and estradiol-like components may interact with gut "satiety hormones" such as peptide YY (PYY) and ghrelin, and thus influence body weight. In a randomized, double-blind, placebo-controlled, cross-over trial with 34 healthy postmenopausal women (59 ± 6 years, BMI: 24.7 ± 2.8 kg/m²), isoflavone-enriched cereal bars (50 mg isoflavones/day; genistein to daidzein ratio 2:1) or non-isoflavone-enriched control bars were consumed for 8 weeks (wash-out period: 8-weeks). Seventeen of the subjects were classified as equol producers. Plasma concentrations of ghrelin and PYY, as well as energy intake and body weight were measured at baseline and after four and eight weeks of each intervention arm.

Results

Body weight increased in both treatment periods (isoflavone: 0.40 ± 0.94 kg, P < 0.001; placebo: 0.66 ± 0.87 kg, P = 0.018), with no significant difference between treatments. No significant differences in energy intake were observed (P = 0.634). PYY significantly increased during isoflavone treatment (51 ± 2 pmol/L vs. 55 ± 2 pmol/L), but not during placebo (52 ± 3 pmol/L vs. 50 ± 2 pmol/L), (P = 0.010 for treatment differences, independent of equol production). Baseline plasma ghrelin was significantly lower in equol producers (110 ± 16 pmol/L) than in equol non-producers (162 ± 17 pmol/L; P = 0.025).

Conclusion

Soy isoflavone supplementation for eight weeks did not significantly reduce energy intake or body weight, even though plasma PYY increased during isoflavone treatment. Ghrelin remained unaffected by isoflavone treatment. A larger and more rigorous appetite experiment might detect smaller differences in energy intake after isoflavone consumption. However, the results of the present study do not indicate that increased PYY has a major role in the regulation of body weight, at least in healthy postmenopausal women.