But my friend lost weight on a cleanse!
This is where things get a bit tricky, because most cleanses do work for people in some way or other. This is thanks to a beautiful mixture of the placebo effect and having a plan.
If you're the kind of person willing to spend money on a supplement, that might give you an incentive to take better care of yourself. Otherwise you're just flushing that money away. So when you get results, you immediately think it’s the supplement that produced the results, not the extra work you weren't doing before.
On top of that, most cleanses come with suggested eating and exercise plans, and the ones that don't are the suddenly ubiquitous juice cleanses, which lead to weight loss because, duh, you're just drinking juice. Not coincidentally, these eating plans almost always focus on eating lots of leafy greens and fruits, avoiding refined carbohydrates, fatty foods, and eating lean proteins.
You might be familiar with this concept -- it's called "a healthy diet."
I don’t care who you are, but if you switch from a diet high in sugar and processed foods to a healthy eating plan using the above criteria, you’re going to drop weight, feel less bloated, and look better. That’s not being cleansed. That’s just a byproduct of being healthier.