Association of run‐in periods with weight loss in obesity randomized controlled trials

Study-level design characteristics that inform the optimal design of obesity randomized controlled trials (RCTs) have been examined in few studies. A pre-randomization run-in period is one such design element that may influence weight loss. We examined 311 obesity RCTs published between January 1, 2007 and July 1, 2009 that examined weight loss or weight gain prevention as a primary or secondary endpoint. Variables included run-in period, pre-post intervention weight loss, study duration (time), intervention type, percent female, and degree of obesity. Linear regression was used to estimate weight loss as a function of 1) run-in (yes/no), and 2) run-in, time, percent female, body mass index, intervention type. Interaction terms were also examined. Approximately nineteen percent (18.6%) of the studies included a run-in period with pharmaceutical studies having the highest frequency. Although all intervention types were associated with weight loss (Mean = 2.80 kg, SD=3.52), the inclusion of a pre-randomization run-in was associated with less weight loss (p=0.0017) compared to studies that did not include a run-in period. However, this association was not consistent across intervention types. Our results imply that in trials primarily targeting weight loss in adults, run-in periods may not be beneficial for improving weight loss outcomes in interventions.