Although many so-called fad diets are unbalanced and don’t live up to their claims, several do. But just because a diet may be effective for weight loss doesn’t mean it’s sustainable long-term.

Fad diets typically promise rapid weight loss and other health benefits, but they can also be restrictive, nutritionally unbalanced, and ineffective over the long term. While some fad diets may be balanced and sustainable, others can potentially lead to nutrient deficiencies and other negative outcomes.

Research suggests certain fad diets may support weight loss in high quality, controlled studies for some people.

Keep reading to learn which fad diets may help support weight loss, which to avoid, and when to talk with a doctor about weight loss.

Fad diets and disordered eating

Research suggests that some popular fad diets may be associated with an increased risk of developing disordered eating patterns.

Many fad diets encourage eating habits that are considered disordered, such as:

  • eliminating entire food groups or macronutrients
  • promoting certain foods as “healthy” and others as “unhealthy”
  • tracking food or calories compulsively

Disordered eating habits can make people feel guilt, anxiety, or disgust around eating that may lead to mental health disorders, disordered eating, and eating disorders.

If you’re preoccupied with food or your weight, feel guilt about food choices, or engage in restrictive diets, consider reaching out for support. These behaviors may indicate a disordered relationship with food or an eating disorder.

Disordered eating and eating disorders can affect anyone, regardless of gender identity, race, age, socioeconomic status, or other identities.

They can be caused by any combination of biological, social, cultural, and environmental factors, not just by exposure to diet culture.

Consider speaking with a healthcare professional or contacting the National Alliance for Eating Disorders, which offers a daytime helpline staffed by licensed therapists and an online search tool for treatment options. For general mental health support at any time, you can call the Substance Abuse and Mental Health Services Administration 24 hours a day at 1-800-662-4357 (or 1-800-487-4889 for TTY).

Fad diets are typically restrictive eating plans that are often unsustainable, or even unsafe, in the long term.

Many deliver short-term weight loss, often due to a loss of water weight, which you regain once you stop the diet.

Dietitians, who are board certified food and nutrition experts, typically recommend making changes to your eating plan that you can maintain long term. They typically recommend eating plans like:

  • The Mediterranean diet: This eating plan emphasizes eating whole foods, lean protein, and various vegetables, fruits, and legumes. It recommends avoiding ultra-processed foods and limiting red meat and dairy.
  • The DASH diet: The Dietary Approaches to Stop Hypertension (DASH) diet focuses on fruits, vegetables, and lean protein and limits salt, sugar, and fat intake.
  • The MIND diet: Mediterranean-DASH Intervention for Neurodegenerative Delay (MIND) diet was developed to reduce the risk of dementia and a decline in brain function as you age. It combines aspects of the Mediterranean and DASH diets.
  • MyPlate eating plan: This eating plan was developed by the U.S. Department of Agriculture to replace the former food pyramid. It involves filling your plate with mostly vegetables, fruits, whole grains, and a smaller amount of protein and dairy.
  • The Harvard diet: The Harvard diet was developed for a study on longevity and combines aspects of the Mediterranean diet and the MyPlate eating plan.

These eating plans support balanced food choices that supply your body with important nutrients. They may also support weight loss along with other lifestyle behaviors, such as regular physical activity and stress management.

A balanced, nutritious diet supplies the nutrients your body needs to function.

If weight loss is a goal, experts typically recommend limiting portion sizes or increasing physical activity to create a calorie deficit between the calories you consume and the calories you expend.

Fad diets typically promise quick weight loss, but are often nutritionally unbalanced and not sustainable in the long term. Many also increase levels of guilt around food and may promote disordered eating.

They also don’t work: People typically regain more than 50% of the weight they lost while on a diet within two years of starting the diet.

Medical Perspective

Diets that limit most foods or sound too good to be true won’t work in the long term, plus they may increase your risk for disordered eating. Instead, make smart choices from every food group. Fruits and vegetables are low in calories yet high in vitamins and minerals. Whole grains, such as brown rice or millet, keep you feeling full longer, dairy products contain essential nutrients like calcium and vitamin D, and fish, chicken, and beans are great sources of protein.

— Jerlyn Jones, MS MPA RDN LD CLT

Learn more about ways to adopt a balanced, sustainable eating pattern.

Quotes represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

Some fad diets to avoid include those that:

  • replace foods with liquids, such as the juice cleanse
  • claim to work “fast” (sustainable, healthy weight loss involves losing 1 to 2 pounds per week)
  • promote detoxification of body systems (your body naturally detoxes itself), such as the liver cleanse and colon cleanse diets
  • are overly restrictive, like the grapefruit diet or those that eliminate entire food groups
  • encourage using supplements that promise to deliver weight loss
  • promote disordered eating by adding moral labels to food and increasing guilt, disgust, or anxiety around eating

It’s always best to get nutrition advice from a licensed dietitian rather than a social media influencer or any person who is making money off “selling” the diet.

Although the ketogenic diet has been called a fad diet, it can be effective for weight loss and may have benefits for people with prediabetes and diabetes.

The ketogenic diet is a very low carb diet that works by lowering insulin levels and shifting your primary fuel source from sugar to ketones. Ketones are compounds made from fatty acids, and your brain and other organs can burn them for energy.

When your body doesn’t have carbs to burn and switches to ketones, you’re in a state called ketosis.

However, unlike other low carb diets, ketogenic diets don’t gradually increase their carbs. Instead, they keep carb intake very low so people following the diet stay in ketosis. The macronutrient distribution typically ranges from approximately:

  • 55% to 60% fat
  • 30% to 35% protein
  • 5% to 10% carbohydrates

That means, in a 2000 kcal per day diet, the carbohydrate allowance would amount to approximately 20 to 50 grams daily.

A 2023 review of research suggests that the ketogenic diet may be an effective treatment for:

  • epilepsy
  • improving blood lipids in people with type 2 diabetes

The researchers note that though some research suggests it may benefit weight loss in people who are overweight or have obesity, the evidence isn’t strong enough to draw conclusions. More research is also needed to determine its long-term safety.

Another review of research notes that while the ketogenic diet may be associated with certain benefits in the first 6 to 12 months, it did not result in additional benefits beyond that, suggesting these benefits may be temporary. In the short term, it was associated with:

The authors also note that despite the diet’s beneficial effect on HDL (high-density lipoprotein) cholesterol, it can also increase LDL (low-density lipoprotein) cholesterol and very-low-density lipoproteins (VLDL), which may increase cardiovascular risks.

Negative health effects

It may also be too restrictive to follow long-term and may have negative health effects, including:

  • lower bone mineral density and increased risk of fractures
  • increased risk of kidney stones
  • hypercalcemia (too much calcium in the blood)
  • low parathyroid hormone, vitamin D, and alkaline phosphate (ALP) levels
  • risk of impaired renal function

Research suggests that low carb diets may be effective for weight loss and provide certain health benefits.

The Atkins diet is another low carb diet with some research behind it. Created by cardiologist Robert Atkins in the early 1970s, the Atkins diet claims to produce rapid weight loss without hunger.

It consists of four stages during which you can consume unlimited amounts of protein and fat:

  • Phase 1 (Induction): During the initial phase, proponents recommend you consume 20 to 25 grams (g) of net carbs per day until you are 15 pounds (lb) or 7 kilograms (kg) from your goal weight. During this phase, your body begins converting fat into ketones and uses them as its main source of energy.
  • Phase 2: You can eat 25 to 50 g of net carbs daily until you are 10 lb (5 kg) from your goal weight.
  • Phase 3: This phase raises your net carb allowance to 50 to 80 g per day until you have met your goal weight and maintained it for 1 month.
  • Phase 4: During the final phase, you can consume 80 to 100 g of net carbs daily to maintain your weight.

For stages 2 through 4, the Atkins diet asks followers to gradually add back their carbs in 5-gram increments to determine their “critical carbohydrate levels” for losing weight and maintaining it.

While most of the research on the Atkins diet is older, research on low carb diets in general suggests that they are effective for weight loss for the first 6 to 12 months. They may also benefit insulin and blood glucose levels and risk factors for cardiovascular disease.

In the famous A TO Z study from 2008, 311 females who were overweight followed the Atkins diet, the low fat Ornish diet, the LEARN diet, or the Zone diet for one year. The Atkins group lost more weight than any other group.

However, more research is still needed to determine whether following these diets long-term is beneficial. Maintaining this diet after 6 to 12 months may have fewer benefits, and more research is needed to better understand its long-term safety.

Negative health effects

The Atkins diet is associated with multiple negative health effects, including:

  • risk of metabolic acidosis (when your body contains too much acid)
  • risk of other metabolic side effects
  • potential for urinary stone formation due to decreased urine pH and calcium balance
  • risk of chronic kidney disease

Like Dr. Atkins, Dr. Arthur Agatston was a cardiologist interested in helping his patients lose weight sustainably without feeling hungry.

He liked certain aspects of the Atkins diet, but was concerned that unrestricted use of saturated fat might increase the risk of heart disease.

Therefore, in the mid-1990s, he created a lower-carb, lower-fat, high protein diet called the South Beach Diet, named for the area in South Florida where he practiced medicine.

Although Stage 1 of the diet is low in carbs and very low in fat, the diet becomes less restrictive in Phases 2 and 3, which allow limited quantities of all types of unprocessed foods while keeping protein intake high.

The diet encourages a high protein intake, because protein may burn more calories during digestion than carbs or fat. Protein stimulates the release of hormones that suppress hunger and help you feel full longer.

A clinical trial from 2021 suggests that high protein, low fat diets led to greater reductions in weight, fat, and triglycerides, and A1c than low fat, standard-protein diets. However, this study didn’t specifically study the South Beach diet.

Although the diet is nutritious overall, it recommends a significant restriction of saturated fat that may not be warranted. It also requires specific planning and may be too restrictive for some people.

Negative health effects

While more research on the South Beach diet is needed, potential negative health effects can include:

The 5:2 diet is a type of intermittent fasting, also known as alternate-day fasting.

On this diet, you eat as you usually would for five days a week and restrict your calorie intake to 500 to 600 calories for two days each week, resulting in an overall calorie deficit that leads to weight loss.

The 5:2 diet is considered a form of modified alternate-day fasting. By contrast, some types of alternate-day fasting involve going without food for a full 24 hours.

The extremely low calorie allotment on the two “fast” days has led some to classify the 5:2 diet as a fad diet.

A 2025 review of research found that the 5:2 diet significantly reduces:

  • body weight
  • body mass index (BMI)
  • waist circumference
  • body fat percentage
  • hip circumference
  • fat mass
  • fat-free mass
  • low-density lipoprotein
  • systolic blood pressure

However, it does not affect total cholesterol, triglycerides, fasting blood glucose, or A1c.

The results of a 2022 pilot study with 131 participants suggest that a 5:2 intermittent fasting plus program was more effective in the short term in weight loss than daily calorie restriction for people who were overweight or had obesity. The members of the intermittent fasting plus group were provided approximately 30% of their energy requirements on fasting days (two non-consecutive days a week) and 70% of their total energy requirements on nonfasting days.

The researchers also note that more studies on long-term adherence to the 5:2 diet are still needed.

This diet requires planning and counting calories to follow its guidelines, which may not be suitable for everyone.

Negative health effects

Intermittent fasting isn’t for everyone. Some of the possible negative health effects can include:

  • fluctuations in free fatty acid levels, which can affect insulin levels
  • reductions in insulin sensitivity
  • increased risk of disordered eating

A vegan diet does not include animal-based products like meat, poultry, fish, or foods derived from animals like dairy or eggs.

It’s important to note that vegan diets can vary widely and may be balanced or unbalanced, depending on the types of foods they contain.

For instance, it’s unlikely that you can lose weight while eating large amounts of processed foods and beverages, even if they contain no animal products.

However, research suggests that whole plant-based vegan diets may support weight loss. They may also have additional benefits, including helping prevent and manage chronic diseases, such as type 2 diabetes and hypertension, supporting the gut microbiome (the healthy bacteria that live in the digestive tract), and improving blood glucose levels.

The results of a two-year study of 151 adults from 2020 suggest that a whole-food plant-based lifestyle program can reduce body mass and body fat percentage. The researchers note that participants maintained the eating plan and experienced benefits for as many as 5 to 10 years following the study. The diet included:

  • whole grains
  • fruits
  • vegetables
  • legumes
  • a moderate intake of nuts, seeds, avocados, and soy (such as tofu)
  • a moderate intake of wheat products with no added fat

It did not allow highly refined carbohydrates (such as white rice and white flour), foods containing added sugars and sweeteners, or animal products.

If you’re planning to follow a plant-based diet, it’s important to ensure you get enough protein from plant-based sources. You can usually work with a doctor or a dietitian to monitor your intake of key nutrients.

Negative health effects

Following a vegan diet may potentially lead to nutrient deficiencies in:

The paleo diet, short for the paleolithic diet, is based on the diets hunter-gatherers ate thousands of years ago.

Paleo has been classified as a fad diet because it restricts many foods, including dairy, legumes, and grains. Critics have pointed out that eating the same foods that our prehistoric ancestors did isn’t practical or even possible.

However, the paleo diet is a balanced eating plan that eliminates processed foods and encourages its followers to eat a wide variety of plant and animal foods. The paleo diet may support weight loss.

A recent review of research suggests it may have benefits for weight loss of 4% to 6% of total body weight within 10 to 12 weeks.

However, the authors also note that this eating plan can be too expensive for many people and may not be nutritionally balanced as it excludes whole grains, legumes, and dairy products. It may not provide enough calcium to meet the daily dietary requirement of 1,000 to 1,200 mg for adults.

A 2021 study involving 18,210 participants from Mediterranean countries followed over 12 years suggests that the paleo diet may reduce the risk of heart disease, likely due to the elimination of ultra-processed foods.

Negative health effects

The paleo diet is associated with the risk of calcium deficiency and may increase certain risk factors for cardiovascular disease, including:

  • decreased HDL “good” cholesterol
  • increased LDL “bad” cholesterol
  • increased blood triglycerides

If you’re concerned about weight loss, it’s best to talk with a healthcare professional about methods that may be safe for you. This is especially important if you are at risk of disordered eating or an eating disorder.

It’s also best to talk with a healthcare professional before drastically changing your eating plan, especially if you have any underlying health conditions. Certain factors, like older age, menopause status, pregnancy, and having diabetes or obesity, can add specific considerations that you should discuss with a doctor.

A doctor may recommend working with a licensed dietitian to develop a balanced, nutritional eating plan that you can maintain long term.

You can start by talking with a primary care physician or family medicine doctor. If needed, they may refer you to other specialists, such as a dietitian or mental health professional.

The bottom line

Fad diets will always be popular, and new plans will continue to be created to address people’s desire to lose weight quickly. However, just because a diet is effective for weight loss doesn’t mean it is sustainable long-term or safe for you.

To achieve and maintain your weight loss goal, it’s important to find a balanced eating plan that you enjoy and can follow for life.

If you need help getting started, it’s best to talk with a healthcare professional, especially if you have any underlying health conditions.