There's a mountain of evidence that suggests that fad diets don't function as permanent weight-loss solutions. So why do we continue to flock toward them when we know they're not very effective? After rounding up the top 10 searched diet plans on Yahoo! and noticing that almost every single one was a fad diet (such as the Atkins Diet, or HCG Diet), we wanted to know more about why we're drawn to these popular diet plans. So we went to Holly Herrington, a Registered Dietitian at the Center for Lifestyle Medicine at the Northwestern University Medical Faculty Foundation to get her take on these plans and whether they really work for weight loss.

"We want a quick fix," Herrington says. "You hear over and over again from dietitians, nutritionists and reputable media outlets that the most sustaining weight loss comes from making lifestyle changes, but as Americans we're drawn to that instant gratification."

When you couple our "want it now" attitude with the fact that the average American gains between seven and 10 pounds during the holiday season (and many never lose that holiday weight), a fad diet that promises a 10-pound weight loss in two weeks can sound very tempting.

"A lot of us are doing it purely for vanity reasons," Herrington says. "We get to the end of the holiday season and realize our jeans don't fit, and we want them to fit."

And if it's weight loss you're looking for, most of these diet plans deliver- temporarily.

"If I'm following a diet plan such as the HCG Diet, where I'm eating 500 calories a day, I'll lose weight," Herrington says. "But I'll lose a lot of water weight, and some muscle, and since I can't sustain that kind of restriction for more than a couple of weeks, I'll probably gain all the weight back when I quit. Not only that, but I'll gain it back as fat, not muscle."

If you really want to lose weight and keep it off, you have to make lifestyle changes, Herrington stresses, such as making exercise a daily part of your life, and slowly cutting back on the amount of calories you're consuming without doing anything drastic like completely eliminating one food group from your diet. Although it's often easier to lose weight quickly than permanently, the reality is that unless you're clinically obese, you should only be losing about one to two pounds per week. Anything more than that is what Herrington calls 'medically inappropriate,' and is considered unhealthy.

Even if you know that slow and steady wins the race, it can be easy to feel as though you're behind the curve when you're working hard to lose weight. What do you think? Have you ever tried a fad diet? Did it work for you?