I tried one if those weight loss food systems once. I'll say it's not really a scam, but if you knew what you were doing, you could do better.
They basically controlled what you could eat so that you ultimately consumed less calories so you could lose weight without having to count calories, or manage macronutrients. But it was also expensive and the food was terrible, and as you said, as soon as you get off of it, you go back to the way you were. ****
However, I do have to thank it for opening my eyes and helping me understand calories and macros a whole lot better. Not to mention proving to me that I could in fact lose weight, back when I thought it was just the way I'd be forever. Because then I started looking into why it worked and what I needed to do to stop buying that crap and eat real food again.
Nope. There's one that actually works really well. It's called 2,4-dinitrophenol. It works by fucking up the way that your body makes/uses ATP; instead of being available for cellular respiration, it gets wasted as heat. It's like constantly doing cardio; you're burning tons of calories without doing anything. Users have reported losing up to seven pounds of fat--not water--in a week. The downside is that this heat can lead to hyperthermia if you take too much, and since the half-life is quite long, by the time you start seeing the negative side effects from OD'ing--about a week after you OD--it's way to late, and your brain cooks. Oh, and you're gonna sweat like a watermelon at a Baptist barbecue the whole time.
It was thought that it also caused cataracts, but that seems to have been incorrect.
It's been banned since the 40s, I think, as a diet pill, because people had a tendency to take too much and die. If you know where to look, you can still find it. I wouldn't recommend it for the overwhelming majority of people though.
Yeah, that's the thing. Weight loss by pill is only possible in a few ways. Diuretics temporarily cause weight loss. The only real options are drugs that decrease your food intake (like the new diabetes drugs), presumably drugs that could interfere with nutrient absorption (not sure if any of those are out there, but it seems like it would be sketchy), or drugs that increase what you burn.
People think that last category could be magic, but burning calories is called burning calories for a reason; it's an oxidation reaction, and it generates heat. There are a few others that also seem to really work, basically all stimulants: nicotine, caffeine, and methamphetamine (which is available by prescription).
Amphetamines both reduce appetite and increase how much energy you expend. Oh, and they're also super addictive. So, yeah, don't use those. I was definitely thinner when I was a smoker, but I had much worse health.
Honestly, the only people I know that use 2, 4-dinitrophenol (DNP) regularly are body builders, and they use incredibly dangerous drugs on the reg anyways, so a diet pill that can kill you if you fuck up is just par for the course. There ain't many old bodybuilders...
Here's just a brief overview of people that have died from it. Since dose is dependent on weight--2-10mg/kg of bodyweight per day, depending on a lot of factors--you can't safely buy pills as a one-dose-fits-all; you would have make your own capsules, and probably have a pretty solid understanding of geometric dilution.