We know how to lose weight: Eat less. Move more. Repeat. The trouble is, that’s incredibly hard to do — which is why lose-weight-quick schemes are so tempting, even though we know better.

This week, the Federal Trade Commission went after several companies that make "deceptive" weight loss claims about their products, in a $34 million lawsuit. Their targets include Sensa, a sort of magic pixie dust you sprinkle over your food, and L’Occitane, which sells a body lotion that promises to make you skinny.

Americans will spend $66 billion this year on weight loss, according to Marketdata Enterprises, up from $58.4 billion in 2010. Obviously, if these weight loss products actually did what they promised, we’d be losing weight, and the demand for diet stuff would fade. But the market research company predicts spending in this area to keep growing 2.7 percent every year through 2016.

“We do this time and again — we want to believe that there is something out there besides eating less and moving more,” says Madelyn Fernstrom, NBC News diet and health editor. “The rational self knows, of course, what we have to do. But we hope, somehow, some magic pill or magic solution will magically melt the pounds off.

“We take leave of our senses when it comes to losing weight,” she says.

Part of what keeps drawing us to weight loss scams is that sometimes they seem to really work – or they do at first, anyway. It’s the placebo effect, Fernstrom says. Take the HCG diet, one of those implicated in the FTC suit. Dieters are injected with a hormone found in the urine of pregnant women, and they’re also instructed to eat only 500 calories a day. If HCG dieters find they’re losing weight, “it’s the 500 calories a day that’s doing it! But people believe they’re less hungry,” Fernstrom says.

As a teenager, Ashley Rozendaal tried it all: the cabbage soup diet, the grapefruit diet, Hydroxycut. “Even though I know that they are unhealthy or they won’t work, I think it happens because of desperation,” Rozendaal says. “I’d tried the healthy ways and it didn’t work as quickly as I’d had hoped. So I turned to these things that made promises.”

In her experience, when you’re trying one of these extreme diets, you do lose weight, but the reason is probably that you’re being more mindful of the foods you’re eating.

“I think that when you’re taking these products, you’re more in tune with what you are consuming,” says Rozendaal, an academic counselor for student athletes in Washingon, D.C. She’s 29, and is also a health blogger; her website is called Coffee Cake and Cardio. “And you’re spending money, so you don’t want to waste your own money. I didn’t want to eat really unhealthy foods when I was spending all this money on all these products.”

The FTC suit goes after the makers of nonsense diet products, and they’re also asking media outlets to stop using the companies’ ads. But while many of us are media savvy enough to spot a shady diet advertisement, we might be more likely to fall for a product or a diet promoted by a favorite “healthy living” blogger. That’s something Rozendaal tries to keep in mind as she writes her own blog, where she's currently promoting the weight loss product Advocare.

“I know that I do have a lot of pull, so I try to really be careful about what I’m sharing with the public,” Rozendaal says. “I do think people need to take what they read online with a grain of salt. I’m not a nutritionist; I’m not a personal trainer. I’m really just sharing my life and journey. My body composition is very different from another person’s.”

The FTC has helpfully posted some guidelines to keep in mind when considering a new weight loss product. But the bottom line is that common sense is key, Fernstrom says.

“We don’t want to accept how hard it is,” Fernstrom says. “Losing weight is hard. We know that. We know that it takes a commitment, but we don’t want to accept this.”