Fad Diets: The Most Popular Ones and Are They Healthy?

Not all diets are healthy. Here’s how to learn to spot a fad diet from one that’s nutritionally sound.

a photo of a broken plate and scattered fork and knife
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The term "diet" has an innocent definition at its core: "habitual nourishment" or "food and drink regularly consumed," per the dictionary. In other words, your diet is how you fuel yourself on a daily basis. Somewhere along the way, diet has also picked up another meaning: what you eat (or don't) to lose weight.

"No wonder it's so confusing," says Molly Bremer, RD, a dietitian with Mind Body Health in Washington, D.C., and northern Virginia. Read on to discover how to tell if a plan might be a fad, get the 411 on some of the most popular fad diets, and learn about the elements of the best diets that can help you live a vibrant, long and restriction-free life.

How to Identify a Fad Diet

Fad diets typically tend to be extreme and restrictive, explains Natalie Rizzo, M.S., RD, a plant-based sports dietitian in New York City and the author of Planted Performance.

Another clue? They also tend to quickly explode with a lot of fanfare: "Suddenly everyone is reporting on or talking about the 'x-diet' and whether it really works," says Frances Largeman-Roth, RDN, a Dobbs Ferry, New York-based registered dietitian and the author of Smoothies & Juices. "The person behind the diet may or may not have real health credentials, which makes it tricky for consumers to avoid them."

There aren't hard and fast ways to pinpoint a fad diet from the rest, but fad diets tend to check several of these boxes, according to a review published in the journal Frontiers in Nutrition in 2022:

  • Promises quick weight loss (to the tune of more than 2 pounds per week
  • Has rigid rules
  • Promotes sales of a specific book or product(s)
  • Recommends short-term changes instead of sustainable routines
  • Zones in on one type of food as "good" or "bad"
  • Suggests cutting out an entire food group
  • Severely restricts calories
  • Doesn't provide proper nutrition
  • Difficult to maintain over the lifespan
  • Fails to offer health warnings or modifications for special populations, such as individuals with chronic diseases
  • Lacks scientific evidence from peer-reviewed studies
  • Provides no maintenance plan once the person following the diet reaches their goal

What to Consider Before Starting a Fad Diet

There are three important questions to ask yourself before diving into a new diet:

  • "What is my motivation to want to try this diet?"
  • "Do I really need to lose weight at all?"
  • "Can I stick with this for a lifetime—and would I feel my best if I did?"

Our bodies are incredibly smart, Bremer confirms, and tend to have a "happy weight" they like to stay around. "The set point theory suggests that there is only so much we can do to change our body size for the long term. It's important to recognize your individual genetic blueprint. Body diversity exists," Bremer says. You'll likely be much happier and healthier if you embrace a lifestyle that feels sustainable—not like a stretch.

The last question (whether this is sustainable for you) is critical. "We know that yo-yo dieting—losing and gaining weight again and again—is not good for overall health. It's much healthier to keep a consistent weight over time," Largeman-Roth adds.

Most Popular Fad Diets

We've seen a lot of fad diets over the years; here are eight of the most well-known:

The South Beach Diet

Created by Arthur Agatston, M.D., and promoted in the 2003 book The South Beach Diet: The Delicious, Doctor-Designed, Foolproof Plan for Fast and Healthy Weight Loss, South Beach is basically a modified low-carb diet that's portioned into sections. For reference, the 2020 to 2025 Dietary Guidelines for Americans suggest consuming 45% to 65% of your calories from carbs. The South Beach Diet maxes out at 28%.

"There are three phases to this diet; two are for weight loss, and one is for weight maintenance," Bremer says.

  • Phase 1: For two weeks, eat three meals and two snacks featuring lean protein, high-fiber vegetables, low-fat dairy and unsaturated fats. Limit carbs and fruit and abstain from juice and alcohol.
  • Phase 2: This is the "long-term weight-loss phase" followers stay in until they reach their goal weight. During this time, dieters are instructed to follow the same basic guidelines of the first phase. There are limited portions of fruit, whole grains and some types of alcohol now allowed.
  • Phase 3: Once users hit their goal weight, they enter a maintenance phase that allows for all foods in moderation, using the basic principles recommended in the earlier stages.

"Carbohydrates are often villainized. In reality, carbohydrates are the body's main source of energy, and they protect our muscle tissue, help our immune system, improve gut health and positively affect mood, sleep and appetite," says Bremer. "Therefore, limiting carbohydrates for the purpose of weight loss affects so many of our physical and mental functions and should not be taken lightly."

Atkins Diet

Atkins made waves in the late 1990s and early 2000s as the original low-carb diet. Originally developed in the 1970s by cardiologist Robert Atkins, M.D., the diet gives recommendations on the number of carbs to eat based on your weight-loss goals.

According to Rizzo, Atkins may help you lose weight, but it's hard to stick with it for the long haul. It also limits many healthy plant-based foods. In turn, you may not get all the vitamins, minerals and fiber you need.

"Many healthy foods, like fruits, vegetables, beans, legumes and grains, are very restricted on this diet. For instance, a half-cup of chickpeas has 20 grams of carbs, which is the maximum amount of carbs you can have in a day if you're on the most extreme version of Atkins or keto," Rizzo says. "That means you can't eat any other carbs that day, including fruits and vegetables."

As a result, both of these fad diets can easily lead to vitamin and mineral deficiencies, as well as constipation from lack of fiber.

Paleo Diet

The paleo diet promotes eating like our ancestors (or, at least, how we think they ate). This diet emphasizes whole foods like grass-fed eggs and meat, plus fish and seafood, fruit, nonstarchy vegetables, nuts, seeds and oils. Processed foods, sweetened drinks, sugar, dairy and grains are off the table. Check out our complete paleo foods list for the full rundown.

"I think this is a bit more sustainable than some of the other diets because there is a wider selection of foods to choose from. That said, I don't see any reason to avoid grains, dairy or legumes," Rizzo says. "Whole grains provide fiber and B vitamins, dairy provides protein and calcium, and legumes are great sources of plant-based protein." (Plus, unless you're allergic or intolerant, it's best to shoot for three servings of dairy daily.)

Raw Food Diet

Even though it has been around since the 1800s, this fad diet seems to resurface every few years, Largeman-Roth says. It's based on eating foods in their raw state, which means that nothing can be cooked above 118 degrees Fahrenheit.

So how does it work? Proponents believe that an ingredient's natural enzymes are destroyed when heated above that level. All raw food dieters can juice raw produce, as well as dehydrate, ferment and sprout fruits and vegetables. Some versions are completely vegan, while others include raw eggs and dairy.

"As a dietitian, this fad diet concerns me because I worry about food safety and if anyone is able to get enough nutrients from this diet. If foods are not allowed to be heated thoroughly, that increases the risk of foodborne illness," Bremer says, especially in regard to raw, unpasteurized eggs and milk.

Eating plenty of produce is certainly part of a healthy, balanced approach to eating, but eating all plant foods raw may not be the best way to go. Research shows that certain nutrients, like beta carotene and lycopene, are actually unlocked when food is cooked, Largeman-Roth adds.

The Macrobiotic Diet

Popular since the 1920s, this mostly plant-based diet focuses on restoring balance and calm within the body. "You eat different things based on gender, age, location and existing health issues," Largeman-Roth explains.

To go macrobiotic, load up on whole grains, legumes and seasonal veggies. Fish, dairy, eggs, poultry and red meat are OK but only occasionally. Steer clear of any and all potatoes, peppers, tropical fruits, tomatoes, caffeine, alcohol, added sugars and processed foods.

"On its face, this is a very healthy diet with heart-health benefits. But in reality, this diet is extremely boring and bland and tends to be low in protein," Largeman-Roth says.

Volumetrics Diet

The term volumetrics was coined by Barbara Rolls, Ph.D., and promoted in a series of books that began in 2009. The guiding force behind this diet plan is to eat foods that fill you up with fewer calories. Fruits, vegetables, whole grains and low-fat dairy products are mainstays.

"Many people love the fact that you can eat tons of certain foods, mainly veggies and soup, and have that very full feeling that so many Americans have become accustomed to from eating large servings," Largeman-Roth says.

While it will likely keep you full, it does categorize food into four groups based on calories, which can affect a healthy relationship with food, Bremer says. And there are plenty of reasons not to count calories. "Food is fuel as well as culture and a social factor in our lives," Bremer continues. "If you're always trying to eat the most voluminous foods, how will that affect your ability to enjoy your trip to Italy, where there's delicious pizza and pasta, or your life at home that involves going out to eat with friends?"

Keto Diet

The keto diet severely restricts carbohydrates to about 5% of calories or 25 total grams of carbs per day. In place of those omitted carbs, dieters are instructed to consume higher amounts of fats and moderate levels of protein. Though this will likely help you lose weight in the short term, people have a difficult time staying on such a restrictive diet.

Bremer notes that there are also some pretty serious long-term risks of being on the keto diet for the long haul, including low blood pressure, kidney stones, nutrient deficiencies and increased risk of heart disease.

The 5:2 Diet

One of several styles of intermittent fasting, the 5:2 diet involves eating as normal for five days per week and fasting the other two (nonconsecutive) days of the week. The fasting days can include up to about 600 calories total, "which isn't much fuel for your brain," Largeman-Roth says.

Some people report positive results after trying this type of fasting; they might feel more energetic and note improvements in blood glucose.

However, for busy, active people, anyone who's growing or parents who need to keep up with kids, "this plan is ridiculous," Largeman-Roth says. Plus, this fad diet is so drastic on the fasting days that it will be really tempting to overeat on non-fasting days "so you may not lose any weight at all," Largeman-Roth adds.

You almost certainly won't have much energy and will feel irritable, and will start to hyperfocus on food and calories. "This style of eating will help you lose weight, but it also could result in binge eating," Rizzo says. "I don't recommend it, and I don't think restricting calories drastically is sustainable in the long term."

The Best and Healthiest Way to Lose Weight

You can absolutely lose weight by cutting your usual food intake in half or eating during only a set window each day. What makes an eating style sustainable, though, is when it can provide your body with adequate nutrition and the essential nutrients you need to thrive, Largeman-Roth says.

It's that sustainable factor that's clutch. The best diet—whether your goal is weight loss, heart health, brain health or longevity—should be something that you feel comfortable keeping up for a lifetime. There's no "finish line" for feeding your body well.

While it's not nearly as sensational as a plan that touts that you can lose 10 pounds in 10 days or get a six-pack in six weeks, "the best diets for weight loss are ones that are well-balanced. They have plenty of proteins, whole grains, fruits, vegetables and healthy fats," Rizzo says. "Eating a variety of whole foods ensures that you get plenty of protein and fiber, two factors that are proven to help keep you full and have been linked to weight loss."

Frequently Asked Questions About Fad Diets

1. What is an example of a fad diet?

Popular fad diets in the past century have included the Atkins diet, keto diet, intermittent fasting, raw food diet, the 5:2 diet and more.

2. Why are fad diets bad for you?

Fad diets often prioritize short-term goals over long-term health. Many fad diets lack certain important nutrients, are severely restrictive in a way that impacts the dieter's quality of life and/or are too low in calories to support important body functions.

3. Which fad diets should you avoid?

Avoid diets that guarantee rapid weight loss, feature strict rules, lack scientific backing, promote the sales of special books or products, declare certain foods or food groups as "bad" or off-limits, drastically restrict calories or the time of day one can consume them, are difficult or impossible to maintain for a lifetime and don't include a maintenance plan.

4. Why are fad diets called this?

Just as fashion fads come and go (are we wearing skinny jeans or wide legs now?), so do diets. Fad diets have earned that moniker because they're popular for a short period of time, and they don't have enough science and results to inspire individuals to stick with them long-term.

The Bottom Line

Unlike overly restrictive fad diets, the best diet shouldn't feel like a "diet" at all. "It's simply a balanced pattern of eating that allows you to be active, participate in celebrations and maintain good health," Largeman-Roth says.

Aim to eat a diverse menu that focuses on adding more whole foods, color, fiber and fun to your plate rather than subtracting hundreds of calories or complete food groups. That's a healthier, happier way to diet.

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