Association between the month of starting a weight management program and weight change in people at high risk of type 2 diabetes: A prospective cohort study

Objective: Weight loss is one of the most common New Year's resolutions, but it is unclear whether attempting to lose weight in January is more successful than attempting it at other times of the year. Methods: In this prospective cohort study from the English National Health Service (NHS) Diabetes Prevention Program, adults with nondiabetic hyperglycemia were enrolled in a structured behavioral weight management program. Repeated measures models assessed the mean difference between baseline and follow-up weight adjusting for monthly variation in weight among those with ≥1 weight measurement. Results: Among 85,514 participants with a mean baseline BMI of 30.3 kg/m2 (range: 13.4 to 84.2), mean weight change at the end of the program after an average 7.9 (SD: 4.5) sessions over 6.4 (SD: 5.6) months was −2.00 kg (95% CI: −2.02 to −1.97 kg) or −2.33% (95% CI: −2.35% to −2.32%). Compared with participants starting in January, participants starting in other months lost less weight, ranging between 0.28 kg (95% CI: 0.10 to 0.45 kg) less weight in those starting in March and 0.71 kg (95% CI: 0.55 to 0.87 kg) less weight in those starting in November. April and May were the only exceptions, in which the estimates followed the same direction but were not statistically significant. Higher session attendance mediated the effects, with participants starting in January attending, on average, 0.2 to 0.7 more sessions than those starting in other months. Conclusions: People starting a weight management program in January lost 12% to 30% more weight than people starting it at other times of the year.