Blundell, J., Finlayson, G., Axelsen, M., Flint, A., Gibbons, C., Kvist, T., & Hjerpsted, J. B. (2017). Effects of once‐weekly semaglutide on appetite, energy intake, control of eating, food preference and body weight in subjects with obesity. Diabetes, Obesity and Metabolism, 19(9), 1242-1251.
Then:
> This randomised, double-blind, placebo-controlled, two-period crossover trial ...
The "randomised, double-blind, placebo-controlled" is a "gold standard" sort of study. Then:
> ... led to a lower ad libitum energy intake during lunch (−1255 kJ; P < .0001) and during the subsequent evening meal ( P = .0401) and snacks ( P = .0034), resulting in a 24% reduction in total energy intake across all ad libitum meals throughout the day (−3036 kJ; P < .0001).
Some pretty big effect sizes.
But they do cite some concerns about the "crossover" portion of the design:
> With regard to changes in weight and body composition, however, this trial could be conversely limited by the crossover design.
And ~30 is a pretty good sample size, as a rule of thumb.
(Disclaimer: I am not a researcher in this area.)