But in reality, bikini season or an upcoming high-school reunion may seem like more concrete and compelling reasons to slim down. And fad diets are always there, offering seemingly easy solutions.
What's more, you can't discount the warm-fuzzy factor when it comes to advice on weight loss, which causes so much anxiety and frustration for so many people. Authors of diet books often try to come off as nurturing and warm, while "official" advice from the government or professional organizations can seem clinical and cold.
Fads Are Nothing New
Although fad diets usually claim to be cutting-edge, most recycle ideas that have been knocking around for a while -- in some cases, more than a century.
"Claims that an author has a permanent solution or a new answer are pretty much bogus, because there's hardly a diet that shows up that hasn't been written about before," says Kelly Brownell, PhD, director of Yale University's Center for Eating and Weight Disorders.
- A high-protein, low-carbohydrate diet was first described in 1863 by William Banting, who took the dieting advice of his friend, a British physician.
- New York doctor William Howard Hay's theory that proteins and carbohydrates should never be combined in a meal was popular in the 1920s and '30s, and it's still popping up in diet books.
- Anyone promoting a "natural" diet is about 170 years too late to claim originality. The Rev. Sylvester Graham started preaching to Americans about natural foods in 1830.
But no matter how far-fetched, faddish ideas continue to appeal to dieters.
"People are very much intrigued by those things that seem to demystify the whole thing -- there's some magic hormone, or there's something in your blood type, you have to eat certain foods together because of how they're metabolized," Osborn says. "That has to be it. It couldn't be something as simple as I need to eat less and I need to exercise more."
Confusion about nutrition is the very reason fad diets exist. If we all knew how to eat, there would be no need for diet books.
"A lot of people may feel out of control and not know what it is they're supposed to do," Osborn says. "Some of the fad diets that are very regimented I think make people feel more comfortable because it takes all the guesswork out."