The way Japan "solves" obesity is quite cruel on those it does not work for. Overweight natives are not treated kindly. I think creating a medicine to make this easier is a moral good, and a sign of kindness and intelligence. Hopefully the aliens also agree.
Some people don't lose weight as easily as others, due to genetics, medical treatment, disability... And even some others have the freedom to not invest as much effort on losing weight.
Point being: there are overweight Japanese, despite the existence of the measures Japan takes to avoid it. These are the people I mean that it doesn't work for. And for those people, they don't have to deal only with the consequences of being overweight, they also have to deal with being treated very poorly. You can say it's for their own good, and the it incentives them to better themselves. Regardless, it still sucks for them.
Shaming people into losing weight may work, on aggregate. I'm not entirely convinced it's a good way to go about it, at the individual level.
Let's be generous and say that a person's body runs on 1600kcal/day, which is pretty low and the other 1800kcal/day which is kinda average. The difference in weight loss between these two over six months eating and exercising is negligible. The maths just doesn't math.
But to be fair It may be psychological. Eating is a very common coping mechanism and not taking care of your body is a common symptom of stress and depression.
Alternative A can have the opposite effect. Unhappy people tend to eat more.
Perhaps it is a "motivator" for people to stop gaining weight by controlling their diet before they are too obese, but once you are obese I think it has mostly negative effects.
Losing significant weight is incredibly hard, and gets harder the more you want to lose. If you have lost 20kg (with great benefits to health) and are still made fun of because you are still above average weight it will have a negative effect and the weight will quickly be gained back
