1 Department of Public Health - Department of Epidemiology, Department of Public Health, Health, Aarhus University2 Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, the Capital Region, Copenhagen, Denmark; Faculty of Medical and Health Sciences, University of Copenhagen, Copenhagen, Denmark.3 Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, The Capital Region, Copenhagen, Denmark.4 Department of Clinical Sciences in Malmö, Diabetes and Cardiovascular Diseases, Genetic Epidemiology, Lund University, Lund, Sweden; Department of Surgical and Perioperative Sciences, Urology and Andrology, Umeå University, Umeå, Sweden.5 Danish Cancer Society, Research Center, Copenhagen, Denmark.6 NUTRIM School for Nutrition, Toxicology and Metabolism, University of Maastricht, Maastricht, the Netherlands.7 Department of Nutrition, Exercise and Sports, NEXS, Faculty of Science, University of Copenhagen, Frederiksberg, Denmark.8 Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospital, The Capital Region, Copenhagen, Denmark; The Novo Nordisk Foundation Centre for Basic Metabolic Research, Faculty of Medical and Health Sciences, University of Copenhagen, Copenhagen, Denmark.9 Department of Public Health - Department of Epidemiology, Department of Public Health, Health, Aarhus University
Reconciling Conflicting Results from Intervention and Observational Studies?
BACKGROUND/OBJECTIVES: Physiological evidence indicates that high-protein diets reduce caloric intake and increase thermogenic response, which may prevent weight gain and regain after weight loss. Clinical trials have shown such effects, whereas observational cohort studies suggest an association between greater protein intake and weight gain. In both types of studies the results are based on average weight changes, and show considerable diversity in both directions. This study investigates whether the discrepancy in the evidence could be due to recruitment of overweight and obese individuals into clinical trials. SUBJECTS/METHODS: Data were available from the European Diet, Obesity and Genes (DiOGenes) post-weight-loss weight-maintenance trial and the Danish Diet, Cancer and Health (DCH) cohort. Participants of the DCH cohort were matched with participants from the DiOGenes trial on gender, diet, and body characteristics. Different subsets of the DCH-participants, comparable with the trial participants, were analyzed for weight maintenance according to the randomization status (high or low protein) of the matched trial participants. RESULTS: Trial participants were generally heavier, had larger waist circumference and larger fat mass than the participants in the entire DCH cohort. A better weight maintenance in the high-protein group compared to the low protein group was observed in the subgroups of the DCH cohort matching body characteristics of the trial participants. CONCLUSION: This modified observational study, minimized the differences between the RCT and observational data with regard to dietary intake, participant characteristics and statistical analysis. Compared with low protein diet the high protein diet was associated with better weight maintenance when individuals with greater body mass index and waist circumference were analyzed. Selecting subsets of large-scale observational cohort studies with similar characteristics as participants in clinical trials may reconcile the otherwise conflicting results.