alt Hacker NewsEven if there are zero effects other than the advertised weight reduction, one downside is obvious from the comments here - some people will stop exercising.
While exercise has many positive effects, which I'd argue are more important than the weight loss, the latter is the primary reason many people exercise and likely to stop when given the weight loss by other means.
We should stop telling people that exercise is a primary driver of weight loss.
That said, exercise has a direct impact on metabolic health which is pretty necessary to maintain a healthy weight.