1. Effect of dietary protein and glycemic index on metabolic syndrome status: The DiOGenes randomized controlled trial Papadaki A a,b, Linardakis M b, Larsen TM c, Damsgaard CT c, van Baak MA d, Jebb, S e, Pfeiffer AFH f, Martinez JA g, Handjieva-Darlenska T h, Kunešová M i, Holst C j, Saris WHM d, Astrup A c, Kafatos A b, on behalf of DiOGenes k a Centre for Exercise, Nutrition and Health Sciences, University of Bristol, UK; b Department of Social Medicine, University of Crete, Heraklion, Greece; c Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark; d Department of Human Biology, Nutrition and Toxicology Research Institute Maastricht, Maastricht University Medical Centre, The Netherlands; e MRC Human Nutrition Research, Cambridge, UK; f Department of Clinical Nutrition, German Institute of Human Nutrition Potsdam-Rehbruecke, Nuthetal, Germany and Charité Universitätsmedizin Berlin, Department of Endocrinology, Diabetes and Nutrition, Berlin, Germany; g Department of Physiology and Nutrition, CIBERobn, University of Navarra, Pamplona, Spain; h Department of Human Nutrition, Dietetics and Metabolic Diseases, National Multiprofile Transport Hospital, Sofia, Bulgaria; i Obesity Management Centre, Institute of Endocrinology, Prague, Czech Republic; j Institute of Preventive Medicine, Copenhagen University Hospitals, Copenhagen, Denmark; k DiOGenes is the acronym of the project ’Diet, Obesity and Genes’, supported by the European Community (Contract no. FOOD-CT-2005-513946), http://www.diogenes-eu.org. Clinical Trial Registration: www.clinicaltrials.gov (number NCT00390637).http://www.diogenes-eu.orgwww.clinicaltrials.gov Poster Reference Number: PO1933 Background and Objectives: Methods: Results: Conclusions: Τhe effect of dietary protein and/or glycemic index (GI) on metabolic syndrome (MetSyn) status has not been investigated in large-scale intervention trials. This study aimed to investigate the effect of weight loss and weight maintenance with diets varying in protein and GI on MetSyn status among adults participating in the DiOGenes study, a randomized, controlled dietary intervention. 938 overweight/obese adults from eight European countries entered an 8-week low- calorie diet (LCD) period. 773 adults who lost ≥ 8% of body weight were randomized to one of five ad libitum diets for 6 months: low-protein (LP)/low-GI (LGI); LP/high-GI (HGI); high- protein (HP)/LGI; HP/HGI; and control diet. MetSyn was defined using the National Cholesterol Education Program criteria (2001). MetSyn status was assessed at baseline, post- LCD and post-intervention, by using a standardized, continuous MetSyn score. A greater absolute decrease in MetSyn score indicates a favourable outcome. Completers’ data was available for 661 (weight loss phase, i.e. baseline and post-LCD) and 434 (weight maintenance phase, i.e. post-LCD and post-intervention) participants. Weight loss during the LCD significantly reduced total MetSyn score (-1.48 vs. -4.45, P<0.001). During weight loss maintenance, changes in MetSyn score differed significantly between the dietary groups, with the highest increase observed in the LP/HGI group (P=0.039, partial η 2 =0.023), supporting earlier evidence that a diet with an increased ratio of protein to carbohydrate that includes low GI foods has beneficial effects on MetSyn in obese individuals. Protein, GI or their interaction did not independently affect MetSyn score. In this sample of European overweight/ obese adults, a moderately-high protein diet, which incorporates low, as opposed to high-GI foods, was beneficial in MetSyn management following weight loss. Keywords: Diogenes, obesity, protein, glycemic index, metabolic syndrome Figure: Mean changes in MetSyn score over the 6-month intervention period