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Fad diets are attractive – especially if one of your goals is weight loss – and they make big promises about your future. But what are fad diets, and why do registered dietitians often advise against them?
“Fad diets are more of a quick fix for weight loss or an acute problem,” says Alyssa Smolen, RDN, based in Essex County, New Jersey. “These differ from therapeutic diets, such as the Mediterranean diet or DASH, which are intended as long-term lifestyle changes,” she says.
It can be difficult to distinguish a fad diet from a sustainable lifestyle diet, especially since in many cases both have “diet” in their names. But that doesn’t make them the same. Here’s how to spot a fad diet, according to Leah Reitmayer, RD, a sports dietitian in Fayetteville, North Carolina.
- Promises rapid weight loss
- Designed as a short-term solution
- Relies on specific foods as a “magic cure” for weight loss
- Excludes certain food groups
- Makes bold claims without scientific support
- An influencer or celebrity claims it worked for them
- It can be expensive to follow
Some fad diets are bizarre at best and dangerous at worst. (But some fad diets have been around for years and may seem credible because of that longevity.) As one study showed, these types of diets can be harmful to your health if you follow them for years. Perhaps it’s because, as the authors note, fad diets often “defy the basic principles of biochemistry and nutritional adequacy.” In other words, they are not scientifically useful and do not provide the nutrients your body needs. Other fad diets may not necessarily be dangerous, but they come with significant pitfalls.
Here’s what you need to know about some of the best and worst options out there.
Best: Keto
The Keto diet – one of the most famous diets of the past decade – is a high-fat, moderate-protein, and very low-carb diet. Because it cuts carbs so rigorously, the diet leads to rapid weight loss, a meta-analysis finds. “People tend to lose weight on a keto diet, but normally this isn’t something that can last long,” says Reitmayer. For example, a study that was part of the meta-analysis cited above found that four to six weeks of the keto diet led to a weight loss of about 20 pounds, although the effect leveled off after six months and long-term results were similar to that of calorie consumption. -restricted eating plan. There are real limitations to keto use. “There are a small number of people who have the discipline to do that in the long term. Our body runs on glucose and that is why we need carbohydrates,” says Reitmayer.
Worst: Carnivore Diet
Do you only want to consume red meat, poultry, fish, butter and eggs? (And water too!) That’s the little list of foods on the carnivore diet. “I would never recommend this diet to anyone,” says Smolen. “You only eat one food group, and restricting so many foods is detrimental to your health. I cannot emphasize enough that variety is necessary for optimal health,” she says. There is increasing evidence that this diet dangerously raises ‘bad’ LDL cholesterol levels. Plus, without plant foods like fruits, vegetables, or legumes, you won’t get fiber, which can lead to gastrointestinal problems, among many other problems.
Best: Vegan
A vegan diet eliminates all animal products, including meat and dairy products. There are many reasons why people try a vegan diet, including ethical ones, where the lifestyle aligns with their values regarding animals and the environment. But there is also a segment of people who use it as a quick weight loss diet – and that’s where it becomes a fad area for some people. Because of this and the fact that the vegan diet can be more expensive and difficult to maintain, it is often not done properly, Reitmayer points out. Although this diet focuses more on what to avoid than what to eat, it is a plant-based diet that protects your heart health and supports a healthy weight, research shows. But that’s only if you follow it carefully; Many highly processed junk foods technically qualify as vegan, and these should be reduced, not increased, in any diet.
Worst: HCG Diet
The HCG diet limits you to 500 calories per day. Dieters also take hormone injections, pellets, sprays, or pills that mimic a hormone produced by the placenta during pregnancy, says Melissa Rifkin, RD, based in Mount Kisco, New York. Proponents claim that the hormone supports weight loss by changing your metabolism. The US Food and Drug Administration (FDA), for its part, says there is no evidence behind it – and any weight loss is due to a lack of food, not the HCG. A big caveat is that if you eat so few calories, you’re probably not getting the vitamins, minerals and proteins your body needs for optimal health. If you possess human chorionic gonadotropin (HCG) in any form, the FDA has this advice: “Stop using it, throw it away, and stop following the dietary instructions.”
Best: intermittent fasting
Intermittent fasting, as it is called, means limiting your eating window. There are different types of intermittent fasting, but many people do 16:8 (a version of time-restricted eating), where they fast for 16 hours and eat for the other eight hours; you can also fast every other day or a few days a week. Compared to other fad diets, a lot of research has been done on intermittent fasting; A meta-analysis shows that these diets are about as effective as calorie-restricted eating. People who participate in a trial tend to stick to intermittent fasting, which is why some find this to be an easier way to reduce overall calorie intake than counting calories to stay within a daily deficit.
Worst: Cabbage Soup Diet Plan
The idea of the cabbage soup diet is to drink cabbage soup for seven days. If you can eat cabbage soup for that long, the promise is that you will lose 10 to 15 pounds. You also get the green light to add some foods during the week, such as apples, berries, brown rice, and beef. “The hype around these single-food diets is quickly fading,” says Rifkin. Even though it’s designed for just seven days, who knows if you’ll even last that long: “The lack of variety bores people,” she adds. Although cabbage is a healthy food in itself, this diet leaves you deficient in fat and protein – two of the three macronutrients necessary for health.
Best: SlimFast Diet
Ranked number five in “Best Quick Diets for Weight Loss” in 2024 by American news and world report, SlimFast won accolades for its efficacy for short-term weight loss. That said, it’s still a fad diet – meal replacement shakes or snacks don’t teach you anything about the often more sustainable approach of a diet rich in fresh, healthy whole foods – and so ranks near the bottom of the ‘Best Diets Overall’ category ‘. “Is it convenient? Certainly. But I do think it is not suitable as a meal replacement,” says Rifkin.
Worst: Sleeping Beauty Diet
The premise of this diet is that you sleep so you don’t eat, which causes you to lose weight, says Reitmayer. It is incredibly dangerous, especially since you are encouraged to take sedatives to allow for extended sleep. Natural sleep is incredibly healthy – and, according to research, necessary for balanced appetite hormones – but this approach counts as disordered eating. Skip it.
Best: Atkins Diet
Atkins and keto can both be low-carb diets, but Atkins stands out because it is high in protein. According to research, this diet also leads to rapid weight loss. American news and world report agrees that it is effective and ranks it at number 2 in the ‘Best Diets for Fast Weight Loss’. But with four phases of the diet, there’s a real learning curve to getting started. Ultimately, the diet is designed to put you into maintenance mode, where you can stick with it for a lifetime – making it one of the better choices. That said, keep in mind that your body needs carbohydrates to thrive, and in the long run it’s difficult to stick to a low-carb diet if you don’t have a medical reason. Another thing to keep in mind is that much of the initial weight loss is water weight due to the carbohydrate restriction, says Smolen.
Worst: Cotton Ball Diet
Another dangerous fad diet, where you consume cotton balls to fill your stomach; In some versions, the cotton is dipped in liquids such as juice before you swallow it. “I almost thought this was a joke, but it’s real, and it’s dangerous,” Rifkin says. Such a ‘diet’ not only deprives you of the nutrients your body needs, but can also cause intestinal blockages, according to OSF Healthcare. No fad is worth risking your health for.