Weight loss plans like Slim-Fast and Weight Watchers are competing hard against free options like calorie-counting apps on smartphones. - 

If you listen to Marketplace every single day, you'll lose 10 pounds a week. We promise. Guaranteed.

Alright, that's a lie, but that is essentially what some diet companies tell Americans in their ads. And the Federal Trade Commission's trying to get tough. It's fined some companies about 30 million dollars total.

But that's just a small drop in the bucket for the industry, according to Lydia DePellis who has been covering the story for the Washington Post. "There's wellness products ... There's steroids. You can peg [the total amount of the industry] from anywhere between $20 billion to hundreds of billions of dollars," DePillis says. "But it's big, to be sure."

One of the big problems is that advertising is mostly self-regulating; advertising platforms like Google are mostly automatic and don't leave much space to regulate true or false claims.

The FTC's ruling focused on deceptive advertising that the companies engaged in. "Most of time, it's not going to hurt them, it's just going to take their money," DePillis says. "But on the other hand, that's people right to pay for what they want as long as they're given true information. Which is the FTC's case. You can't lie to someone and say it's going to solve all your problems and you can eat all the food you want if it's not." 

Follow Kai Ryssdal at @kairyssdal