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Fad diets are tempting – especially if weight loss is one of your goals – and they make big promises about your future. But what are fad diets, and why do registered dietitians tend to advise against them?
“Fad diets are 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 or DASH diet, which are intended to be long-term lifestyle changes,” she says.
It can be difficult to tell a fad diet from a sustainable lifestyle diet, especially since both have “diet” in their name in many cases. But that doesn’t make them the same. Here’s how to spot a fad diet, according to Leah Reitmayer, RD, a sports nutritionist in Fayetteville, North Carolina.
- promises fast weight loss
- Designed as a short term solution
- Relying on specific foods as a “magic cure” for weight loss
- It excludes certain food groups
- Bold claims without scientific support
- A celebrity claims it worked for them
- May be expensive to follow
Some fad diets are weird at best and dangerous at worst. (But some fad diets have been around for years and may appear to have credibility because of that longevity.) As one study has shown, these types of diets can be harmful for your health if you follow them for years. Perhaps it’s because, as the authors point out, fad diets often “violate basic principles of biochemistry and nutritional adequacy.” In other words: They don’t make scientific sense and they don’t provide the nutrients your body needs. Other fad diets may not be inherently dangerous, but they have 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 last decade – is a high-fat, moderate-protein and very low-carbohydrate diet. Because it cuts carbs so severely, the diet tends to produce rapid weight loss, a meta-analysis points out. “People tend to lose weight on a keto diet, but it’s usually not something that will last,” says Reitmayer. For example:One study included in the meta-analysis cited above found that four to six weeks of a keto diet resulted in a weight loss of about 20 pounds, although the effect diminished after after six months and that long-term results were similar to calorie. – restricted eating plan. Going keto has real limits. “There are a small number of people who have the discipline to do that long term. Our bodies run on glucose, so we need carbohydrates,” says Reitmayer.
worst: Carnivore Diet
Do you want to eat only red meat, poultry, fish, butter and eggs? (And water, too!) That’s the small list of foods on the carnivore diet. “I would never recommend this diet to anyone,” says Smolen. “You’re only eating one food group, and restricting so many foods is bad for your health. I can’t stress enough the importance of variety for optimal health,” she says. Evidence is emerging that this diet dangerously raises levels of “bad” LDL cholesterol. In addition, without any plant foods, such as fruits, vegetables, or legumes, you are not getting fiber, which can lead to GI problems, among many other issues.
Favorite: Vegan
A vegan diet eliminates all animal products, including meat and dairy. There are many reasons why people follow a vegan diet, including ethical ones, where the lifestyle is in line with their values regarding animals and the environment. But there is a subset of people who use it as a quick weight loss diet – and that’s where it veers into fad territory 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 correctly, Reitmayer points out. Although this diet focuses more on what to avoid, rather than what to eat, it is a plant-based diet that protects your heart health and has been found to support a healthy weight, research notes. But that’s only if you’re following it right; A lot of highly processed junk food technically qualifies as vegan, and those should be cut back in any diet, not increased.
Worst: HCG Diet
The HCG diet limits you to 500 calories per day. People on the diet 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. For his part, the US Food and Drug Administration (FDA) says that there is no evidence behind it – and any weight loss comes from a lack of food, not HCG. A huge caveat is that you likely won’t get the vitamins, minerals and protein your body needs for optimal health when you’re eating that many calories. If you have 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: Light Fasting
Intermittent fasting, as it is called, means that you restrict your eating window. There are many types of intermittent fasting, but many people do 16:8 (a version of time-restricted eating), where they fast for 16 hours and eat during the other eight; you can also fast every other day or a few days a week. Compared to other duration diets, research on intermittent fasting is strong; a meta-analysis shows that these diets are almost as effective as a calorie-restricted diet. People in trials are usually able to stick to intermittent fasting, so some people find that this is an easier way to reduce total calorie intake than counting calories to stay in a daily deficit.
worst: cabbage soup diet plan
The idea with the cabbage soup diet is to guzzle cabbage soup for seven days straight. If you can eat cabbage soup for that long, the promise is that you will lose 10 to 15 pounds. You are also given the green light to add some foods during the week, such as apples, berries, brown rice and beef. “The hype with these individual diets burns out quickly,” says Rifkin. Although it’s only designed for seven days, who knows if you can survive that long: “The lack of variety tends to drive people away,” she says. Although cabbage itself is a healthy food, this diet lacks fat and protein – two of the three macronutrients needed for health.
Best: SlimFast Diet
Ranked number five in the “Best Diets for Weight Loss” in 2024 by US News & World Report, SlimFast won honors for its effectiveness 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 to a diet rich in fresh, healthy whole foods – so it’s near the bottom of the “Best Diets Overall” category. “Is it convenient? Definitely. But I think it’s not enough as a replacement food,” 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 extremely dangerous, especially since you are advised to take sedatives to make a long sleep better. Natural sleep is extremely healthy – and is essential for balanced appetite hormones, according to research – but this approach counts as disordered eating. Skip it.
Best: Atkins Diet
Atkins and keto may be low carb diets, but Atkins is different in that it is high in protein. This diet also leads to rapid weight loss, according to research. US News & World Report Agree that it is effective, it ranks No. 2 in “Best Weight Loss Essays.” But with four phases of the diet, there’s a real learning curve to getting started. Ultimately, the diet is designed to put you in maintenance mode where you’ll stay on it for life – making it one of the best options. That said, keep in mind that your body needs carbs to thrive, and long-term, it’s hard to stick to a low-carb eating plan when 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 carb restriction, says Smolen.
worst: Cotton ball diet
Another dangerous fad diet, this involves throwing cotton balls to fill your stomach; some versions involve dipping the cotton into liquids such as juice before swallowing. “I almost thought this was a joke, but it’s true, and it’s dangerous,” says Rifkin. A “diet” like this not only robs you of the nutrients your body needs, but it can cause intestinal blockages, according to OSF Healthcare. It’s not worth risking your health.
