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Fad diets are not a new phenomenon, and with the prevalence of obesity in the U.S. rising to nearly 42% of the population between 2017 and 2022, it’s no surprise that an estimated 45 million Americans go on a diet every year[1]
While many diet programs can be followed in a healthy way, fad diets, which are often marketed as a “quick fix” for weight loss, are typically backed by little scientific evidence supporting their efficacy and safety. Some research even suggests following these diets in the long term could lead to negative health consequences.
While experts recommend steering clear of most fad diets, several are supported by some research. This article highlights the potential benefits and drawbacks of some of the more popular fad diets.
Keep in mind that while these fad diets may help you lose weight in the short term, experts generally agree that there are healthier, more sustainable ways to lose weight and lower your risk of chronic disease.
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What Is a Fad Diet?
A fad diet is a popular dietary pattern that claims to help you lose weight quickly.
“Fad diets can usually be identified by having a tight set of rules the person should be following,” explains registered dietitian Emily Tills, a virtual nutrition coach based in Syracuse, New York. “Usually there’s a ‘good foods’ and ‘bad foods’ list, and people plan on following the diet briefly before returning to their previous eating patterns once they reach their goals,” she adds.
According to research, fad diets tend to have the following characteristics:
- A promise of rapid weight loss
- A lack of physical activity guidelines
- Promotion of short-term changes rather than achieving lifelong goals
- A focus on one type of food or elimination of certain food groups
- Unsustainability in the long term
- Nutritional inadequacy
- A failure to provide health warnings for those with chronic diseases
- A lack of scientific evidence to support claims
Some fad diets, such as the cabbage soup diet or the military diet, make claims that defy basic principles of biochemistry and nutritional adequacy. Conversely, others like the South Beach Diet or intermittent fasting encourage some healthy eating patterns—like limiting consumption of processed foods—and are grounded in research that supports their efficacy from both a weight loss and overall health standpoint.
However, even fad diets that are more research-based may not be sustainable in the long term.
“Fad diets involve unrealistic or unsustainable practices, such as cutting out entire food groups or only consuming liquid meals. These diets often promise quick or dramatic weight loss, but don’t offer long-term success,” explains Gabriela Rodríguez Ruiz, M.D., a board-certified bariatric surgeon at VIDA Wellness and Beauty in Tijuana.
Fad Diet Examples
Here’s a rundown of some of the more popular fad diets out there, their potential benefits and drawbacks, and how they work for weight loss.
The Paleo Diet
Introduced in 1985, the paleo diet aims to mimic the dietary patterns of humans prior to agricultural development. It claims humans should eat foods similar to those we evolved with and avoid foods we didn’t have access to during our evolution.
Followers of the paleo diet are instructed to eat as many lean meats, fruits and non-starchy vegetables as they want, as well as eggs sparingly. Dairy products, legumes, grains and processed foods are strictly off limits. The paleo diet doesn’t focus on portion size or caloric intake.
Because it limits intake of the most significant sources of carbohydrates in the standard American diet—cereals, legumes, dairy and processed foods—the paleo diet is essentially a low-carbohydrate diet.
The Keto Diet
The ketogenic diet was originally designed in 1923 by physician Russell Wilder as an effective treatment for epilepsy.
Several variations of the keto diet exist today, but generally, it’s a very low-carbohydrate diet (VLCD) featuring a moderate amount of protein, high amounts of fat and no more than 5% to 10% of one’s daily calories from carbohydrates. Someone following a 2,000-calorie diet can consume no more than 200 calories—or 50 grams—of carbohydrates a day on the keto diet.
The body typically uses glucose as its primary energy source. When you severely limit your intake of carbohydrates, you use up your glucose stores and your body relies on ketone bodies as an alternate energy source, a process known as ketosis. When the body reaches ketosis, insulin secretion decreases, helping to reduce fat and glucose storage.
Studies show a medically-supervised ketogenic diet can be effective at improving symptoms and quality of life for a variety of conditions, including epilepsy and other neurological disorders. More recently, people have adopted a keto diet in an effort to lose weight, though studies are mixed on whether it’s more effective than traditional weight loss diets.
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The Atkins Diet
Cardiologist Robert Atkins developed the low-carb, high-protein Atkins diet in the 1970s. Followers are instructed to limit their consumption of carbohydrates to less than 5% of their total daily caloric intake—less than 100 calories (25 grams) of carbohydrates for someone following a 2,000-calorie diet. People following the Atkins diet are also instructed to eat as much protein and fat as they want, drink plenty of fluids, supplement with vitamins and minerals, and incorporate regular exercise.
The Atkins diet is appealing because it makes it easy to feel full, and limited food choices make meal planning simple, notes Cleveland-based sports dietitian and functional nutritionist Kylene Bogden, co-founder of FWDfuel and Pureboost ambassador. But it is “easy to fall under the trap of buying all processed, pre-packaged foods labeled as ‘Atkins’ for convenience,” she adds.
As with any high-protein, low-carb diet, Atkins isn’t ideal for heart and gut health due to a potentially high intake of saturated fat and lack of fiber, notes Bogden.
The South Beach Diet
The South Beach diet is a three-stage, modified low-carbohydrate weight loss diet plan developed in 2003 by Dr. Arthur Agatston.
During phase one, followers avoid eating most carbohydrates and focus on lean protein, high-fiber vegetables and healthy fat sources. In phase two, followers of the diet reintroduce some foods that were eliminated, including whole grains, fruits and other vegetables. Phase three is a maintenance diet that can be followed indefinitely.
Followers of the diet are instructed to eat three balanced meals and three snacks throughout the day. The diet advises eating until hunger is satisfied using the provided meal plans and recipes.
The early phases of the diet are a low-carbohydrate, high-protein eating plan. According to Bogden, the South Beach diet “promotes a great macronutrient ratio of moderate carbohydrate, higher protein and fat, promoting greater satiety and better blood sugar balance.”
Intermittent Fasting
Unlike diets that focus on restricting the number of calories you eat, intermittent fasting sets guidelines for when you can eat—not what or how much. Typical intermittent fasting alternates avoiding all food for a certain amount of time with periods of normal eating.
The most popular intermittent fasting periods include:
- Alternate day fasting, in which a day of fasting, or eating less than 25% of your total caloric needs, alternates with a day of normal eating.
- Periodic fasting, or the 5:2 diet, in which you fast or eat less than 25% of your total caloric needs for two non-consecutive days of the week, with normal eating the other five days of the week.
- Time-restricted feeding, in which you eat normally within a specified window of no more than eight hours per day.
Intermittent fasting may work because when you restrict the hours you’re able to eat, you end up restricting your overall caloric intake. “Limiting when you can eat may help break unhealthy habits like mindlessly snacking late at night,” explains Liz Cook, M.S., a registered dietitian at OnPoint Nutrition in Pittsburgh, Pennsylvania. But she cautions that fasting too long between meals can cause low blood sugar, which can lead to mood swings, headaches and, more seriously, shakiness, dizziness, confusion and anxiety.
The Whole30 Diet
Whole30 is an elimination diet that features two phases. The first phase involves 30 days of eating only meat, seafood, eggs, vegetables, fruits, “natural” fats, herbs, spices and seasonings. The following 10 days focus on reintroducing eliminated foods one at a time to see how they affect your energy, sleep, mood, cravings, digestion and other symptoms.
Whole30 isn’t designed for weight loss, nor is it designed to be followed in the long term. Instead, the goal is to identify food sensitivities. It’s promoted as a “reset.”
Whole30 requires that followers commit and strictly adhere to its protocol for 30 days. The program’s website states that if you eat even a bite of a food or beverage that isn’t allowed on the plan, you must start over again from day one.
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Potential Side Effects of Fad Diets
Before starting a fad diet, it’s important to consider its long-term outlook and potential side effects.
While fad diets may lead to weight loss, evidence suggests most people regain this weight soon after stopping the diet. And since many of these diets are short-term plans instead of long-term lifestyle interventions, they’re less likely to result in long-term weight loss.
Indeed, a review of 29 long-term weight loss studies found that within two years, participants maintained only 44% of the weight they initially lost. By five years, they maintained only 21% of their initial weight loss[3].
When you lose weight, your resting metabolic rate—the amount of calories your body burns at rest—slows. Some believe rapid weight loss—like that promoted by fad diets—may slow metabolic rate even further, making it difficult to keep the weight off and future weight loss more challenging.
Also, with their strict food rules and unusual eating patterns, fad diets can be difficult to stick with in the long term.
“My number one recommendation before starting any diet or eating plan is to ask yourself, ‘Can I do this forever?’ If the answer is no, it’s likely not something that will get you where you’re trying to go,” advises Cook.
Further, fad diets that eliminate whole food groups run the risk of not being nutritionally balanced. “I do not recommend these diets in the long term. Many eliminate whole food groups, which can lead to deficiencies in macronutrients and micronutrients. For example, keto and Atkins are low in fiber and can lead to poor digestion,” explains Cook.
Additionally, emerging evidence suggests an association between certain low-carbohydrate diets and decreased lifespan. A large prospective cohort study examining the effects of carbohydrate intake on mortality followed 15,428 adults for 25 years. Low-carbohydrate dietary patterns (where less than 40% of one’s daily energy stemmed from carbohydrate consumption) that favored protein and fat from animal sources were associated with increased mortality and shorter lifespan. In contrast, low-carbohydrate diets that emphasized plant-derived protein and fat were actually associated with decreased mortality and longer lifespan[4].
On the flip side, high-carb diets with greater than 70% of energy from carbohydrates were also associated with increased mortality and shorter lifespan. Diets with moderate amounts of carbohydrate intake between 50 to 55% of total energy were associated with the least risk of mortality.
This study suggests that diets with a moderate intake of carbohydrates and low-carbohydrate plant-based diets may be better choices for healthy aging and longevity. Further, the research has implications for diets like keto and Atkins, which are very low-carbohydrate diets that limit consumption of fruits and vegetables and tend to favor animal products as sources of protein and fat rather than plant-based options.
The diets themselves may also present side effects. For example, research indicates the ketogenic diet can lead to the following complications in the early days, weeks or months of starting the diet:
- Chronic fatigue
- Nausea
- Headaches
- Hair loss
- Reduced alcohol tolerance
- Reduced physical performance
- Heart palpitations
- Leg cramps
- Dry mouth
- Bad taste
- Bad breath
- Gout
- Constipation
Finally, beyond the physical risks, fad diets may negatively affect a person’s relationship with food and eating. “In order to properly follow one of these diets, we have to purposefully create habits that [can] lead to obsessive thinking about food and weight,” notes Las Vegas-based psychotherapist Lauren Ball, who specializes in disordered eating.
“Fad diets leave a person measuring, counting, reviewing ingredients, excessively weighing, checking packages, checking the time, avoiding portions of the grocery store and avoiding or being anxious about restaurants and social outings. Over time, a person can start to create irrational fears and behaviors around food and weight. Eating can become stressful, tracking and checking obsessions can become excessive, and the anxiety surrounding food and the fear of weight can take over,” she adds.
How to Choose the Best Diet for You
The most effective diet is one you can stick to in the long term. “We need to focus less on short-term looks and more on long-term lifestyle,” explains Dana Ellis Hunnes Ph.D, a senior clinical dietitian at UCLA Medical Center, assistant professor at UCLA Fielding School of Public Health and author of Recipe For Survival.
Hunnes recommends focusing on lifestyle choices and adopting a whole food, plant-based or Mediterranean diet, which research shows can increase longevity and lower risk of chronic diseases like heart disease, diabetes, stroke and certain cancers.
People should be cautious about jumping on the latest fad diet bandwagon and instead focus on making long-term, sustainable changes to eating habits through a balanced, nutrient-rich diet along with regular physical activity, agrees Dr. Rodriquez Ruiz. “Healthy lifestyle habits—not quick fixes—are the key to lasting weight loss success,” she adds.
Finally, if you’re considering making a big change to your eating habits, it’s always a good idea to speak with a registered dietitian or doctor to learn about proper techniques, recommendations that work with your personal or cultural eating patterns and any individual health concerns.
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