Remember: There's no quick fix or miracle plan for weight loss.

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What do you think of when you think of a fad diet? Many people probably think of old-school fads like eating nothing but grapefruit all day, drinking gallons of cabbage soup, or stocking up on meal-replacement shakes. But really, fad diets aren't all so gimmicky—and there's a chance you've probably tried one before.

According to the Cleveland Clinic, “fad diets are plans sold as the best and fastest approach to losing weight.” Many of today’s popular diets fit this bill, although they send mixed messages. On the one hand, they promise to be miracle solutions for quick weight loss. On the other hand, they claim to be holistic and sustainable approaches.

But no matter how differently fad diets market themselves, there's one thing that they all have in common: They might lead to quick weight loss, but they largely fail in the end. Below is a little more about why fad diets aren't really the miracle cures they promise to be—and why you should steer clear.

Reason #1: No fad diet is truly new or unique

Anyone who's been paying attention to popular diets for more than a few years has probably noticed that every new fad diet is really just a recycled and repackaged version of an old diet—and yet, each one claims to be special and unique.

Some diets, for example—like the F-Factor diet, which caused a bit of controversy in 2020—focus on increasing the amount of fiber in your diet. (The F-Factor diet's website actually says it's "the only dietitian-created program for weight-loss and optimal health that is based on fiber-rich nutrition.") In general, it's sound advice, but loads of other reputable health organizations—like the US Department of Agriculture, the American Diabetes Association, the American Heart Association, the Institute of Medicine, and the Academy of Nutrition and Dietetics—also recommend fiber-rich nutrition.

Other eating plans tout their own uniqueness while throwing other diets under the bus—despite sharing similar traits. The Dukan Diet, for example (which was recently named 2021's worst diet, according to US News and World Report) recognizes that "95% of people who diet gain all the weight back... and more when they return to their old eating habits," according to the diet's website—but goes on to say that the Dukan Diet specifically "will redesign your eating habits and help you permanently stabilize your weight." However, that diet is similar to the South Beach Diet, in that they both offer a low-carb diet plan that depends on phases.

Of course, those are only two examples of a laundry list of fad diets that share similarities. But it goes to show that most fad diets rely on nutrients to include or exclude, specific programming consideration to follow, and the claim that their program works better than others—all of which actually unites them.

Reason #2: No one nutrient is better than another

Speaking of nutrients, another thing many fad diets have in common is that they vilify certain foods or nutrients while glorifying others. In fact, most diets tend to focus—either negatively or positively—on a select few nutrients. But dietitians warn against this type of thinking.

"Our bodies need a variety of foods," Shana Minei Spence, MS, RDN, a dietitian based in New York City, tells Health. She explains that different foods have different macronutrients (carbs, fat, and protein), vitamins, and minerals, and that variety is what keeps us healthy. Carbs break down into glucose, our body's primary source of energy, and often come with fiber that keeps our digestive systems working properly. And "we need protein for our muscles and fat for organ protection and nutrient absorption," Spence says.

Most of today's fad diets take a low-carb and high-protein approach and throw shade at the low-fat diets of decades past. But really, the evidence shows that low-carb, high-protein diets aren't any more effective for weight loss than low-fat diets. A 2018 review of the existing evidence published in the journal Healthcare finds that limiting certain macronutrients isn't more effective for weight loss in the long term than just eating fewer calories. Low-fat diets, low-carb diets, and high-protein diets all lead to about the same amount of weight loss over a 12 months period. Study participants on these diets are also more likely to drop out of a study over the course of a year than those on diets that just focus on eating fewer calories, because these restrictive diets are much harder to stick to.

Reason #3: Fad diets often sell products, which is a red flag

Many, many diets sell snacks and ready-made meals to go along with their eating plans—that includes, but isn't limited to, the South Beach Diet, the F-Factor diet, Atkins, and even Whole30. It seems easy and accessible, but here's the thing: Anyone who creates a fad diet and sells products is also making a lot of money. The US weight loss market is worth $72 billion, so there's real financial incentive to create fad diets that sell books and products.

On the other hand, evidence-based advice like eating more nutritious foods and fewer processed ones doesn't lead to massive profit—but it is a better route if you're looking for results. In a review of the Optavia diet for Health, Cynthia Sass, RD, MPH, points out that the amount of processed foods and snacks offered by these diets is problematic since it prevents people from having healthier fresh food options. "Processed diet products also contain common allergies," she said, adding that soy is a common allergen found in those types of foods. Diet snacks also tend to use intense sweeteners, like monk fruit and stevia (which are about 200 times sweeter than actual sugar), and in turn, may disrupt appetite regulation or make natural foods taste less sweet, she said.

While we're on the topic of selling diet products, it's important to look at the marketing of these products too. Many commercials and advertisements show young, thin (and often cis-gender and white) people being active and enjoying these products, implying that they will help you achieve the same look. Of course, they won't; those people don't look that way because they're on the diet, they look that way because of their genetics, their circumstances, and a host of lifestyle factors. Heck, they might not even be on the advertised diet at all.

Reason #4: Very restrictive diets produce quick but unsustainable results

Search #keto on Instagram and you’ll find thousands of people who claim that the diet has helped them lose huge amounts of weight in a short period of time. That’s likely true: Research shows that people often lose up to 10 pounds in their first two weeks on a keto diet (high-fat, moderate-protein, very low-carb). But long-term compliance is extremely difficult, and weight loss tapers off after these first few weeks. The same is true for all restrictive fad diets. “Diets always start off as exciting because people are thinking that this is the answer for them,” Spence says. “The excitement wears off quickly, especially when people realize how little they are ‘allowed’ to eat.”

There's evidence to back this up. A 2020 meta-analysis published in The BMJ looked at 121 weight loss studies and found that the vast majority of people on any weight loss diet typically lose a significant amount of weight after six months, but regained most of that weight in the next six months. And while compliance is a factor, it's not the only one. A 2015 review study published in the International Journal of Obesity explains that your body actually resists weight loss by burning fewer calories, increasing production of ghrelin (a hormone that makes you hungry), and decreasing production of leptin (a hormone that makes you feel full).

Ultimately, there are so many factors that contribute to your weight and whether or not long-term weight loss is possible. Most weight loss studies last 12 months or less, so it's hard to know how many people are actually able to lose weight and keep it off. Another consistent finding in the research is that the sustainability of a diet is a better predictor of success than anything else—a 2014 review published in JAMA looked at 59 weight loss studies and concluded that the most successful diet is any diet that a person can stick to long-term. That might look different for each person, but sustainable diets have a few things in common. In the aforementioned 2018 review in Healthcare, the authors came to a simple conclusion: "A healthy diet is a varied diet rich in fruits, vegetables, whole-grain products and high-quality proteins and poor in added sugar, refined grains, and highly-processed foods," adding that people who eat this way find it easier to control their weight.

Now that you know how to sniff out fad diets, make a commitment to steer clear

Look, we live in a diet- and weight-obsessed world. It's natural to want to believe that the next fad diet will be The One, even if you know deep down that they're all selling the same thing. Instead of falling victim to the next plan that comes along, remember that nutrition science is already very clear on what a healthy, sustainable diet looks like: plenty of fruits, vegetables, whole grains, nuts, seeds, and legumes, and limited added sugar, saturated fat, and processed food.

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