Fad diets have a seductive allure. With promises to "personalize your nutrition" or "achieve your best shape", they offer a solid set of rules that can make men and women feel like they’re on a fast-track to fitness. Fad diets also change from year to year, giving the illusion of progress. A fad diet can be loosely described as any weight loss plan that gains quick — and often temporary — popularity.

But nutrition research is a science and like all science, its evidence must be looked at with a critical and open eye. Dr. Scott Kahan, director of the National Center for Weight and Wellness warns dieters to use “due diligence” when it comes to believing everything they read. “Fad diets prey on people who feel helpless about managing their weight and health,” Kahan told Medical Daily. “By making miraculous claims and then letting people down, [they] ultimately demoralize patients from moving forward. They get in the way of people finding a reasonable, balanced, healthful approach to managing weight.”

The diet industry is, after all, an industry. The U.S. weight-loss market pulled in revenue of $60.5 billion in 2013 according to MarketResearch.com, made mainly from diet books, drinks, surgeries, and programs. MarketResearch also notes a larger shift toward Do-it-yourself (DIY) dieting, meaning that more people are taking their nutrition into their own hands. If this is the case, knowing what’s true and what’s not becomes all the more important.

So how can we weed out a fad diet from a healthy one, and truly embody what it means to "eat clean"?

The first step is to remember that a diet does not always equal balanced, healthy eating. Roy Pumphrey, a strength and conditioning specialist at John Hopkins University names several signs to look out for when identifying fad diets:

Fad diets tend to deal in extremism

According to Pumphrey dieters should be wary of plans “omitting entire categories or types of food.” The American Heart Association (AHA) cites the Cabbage Soup Diet as one such diet. The Cabbage Soup diet encourages people to drink the fat-burning cabbage soup with a limited amount of fruits and vegetables for seven days, effectively eliminating valuable nutrients like calcium, iron, zinc, and vitamin B. And while dieters do indeed lose weight quickly, they regain the fat shortly after, since the weight was lost in water, not fat.

“[Quick weight-loss diets] violate the first principle of good nutrition: Eat a balanced diet that includes a variety of foods,” the AHA writes on its website. “If you are able to stay on such a diet for more than a few weeks, you may develop nutritional deficiencies, because no one type of food has all the nutrients you need for good health.”

Fad diets claim to 'cure' certain illness without clinical evidence

Like Pumphrey, Kahan is wary of diets that lack scientific evidence to support their claims. Kahan warns dieters of the "Eat Right for Your Type" diet, a plan designed by Dr. D’Adamo that claims you should follow a particular eating and exercise plan based on your blood type. “The Eat Right for Your Type diet has no scientific backing to my knowledge,” Kahan says. Pumphrey agrees, saying that it’s a common but untrue claim that blood type affects how food is digested, processed, and used in the body.

Kahan also mentions Herbalife, which he says “makes all sorts of miraculous claims that aren’t supported by scientific evidence.” Herbalife sells shakes and supplements for weight loss, skin care, and digestion — meant to accompany one meal a day. Multiple personal blogs and websites describe the harmful side effects of Herbalife. “Herbalife also has a significant conflict of interest as a mid-level marketing program where the counselors are paid to sell the product,” Kahan added.

These diets hit another red flag of Pumphrey’s: fad diets that rely solely on anecdotal evidence and testimonials to prove their effectiveness. Pumphrey has several other red flags, most of which would apply to the diets mentioned above:

  • Fad diets that promise quick fixes
  • Fad diets that ignore the differences between individual people, such as individual body composition or activity level.

Kahan adds that many “detox” or colonic diets are “just plain dangerous”, since they could lead to severe dehydration and electrolyte imbalances. And when it comes to spotting a fad diet, Kahan has his own advice.

“For one, anything that looks too good to be true,” Kahan said. “Second, if a certain diet or product or weight loss program isn’t supported by genuine obesity experts, it’s likely a bogus fad. There are many treatments that really do work, and these are regularly used clinically by experts.”