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Assorted ketogenic diet foods on a dark tray, including salmon fillets, eggs, avocado, various cheeses, nuts, seeds, spinach, broccoli, and a bowl of nut butter. Assortment of protein-rich foods on a wooden table, including salmon, beef, chicken breast, eggs, milk, cheese, beans, and almonds.
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Typical ketogenic diet foods
Typical ketogenic diet foods The ketogenic diet restricts carbohydrates to promote fat metabolism through ketosis. It is typically focused on the consumption of meats, eggs, cheese, nuts, oils, and low-carbohydrate vegetables.

fad diet

nutrition
Written by
Kara Rogers
Kara Rogers is the senior editor of biomedical sciences at Encyclopædia Britannica, where she oversees a range of content from medicine and genetics to microorganisms. She joined Britannica in 2006 and...
Kara Rogers
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Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
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Top Questions

What is a fad diet?

What are some popular fad diets?

What are some health concerns associated with fad diets?

fad diet, any of various eating plans that promote rapid weight loss or other health benefits through highly restrictive, unconventional, or narrowly focused dietary practices. Typically characterized by claims of quick and dramatic results, fad diets often eliminate entire food groups, emphasize specific “superfoods,” or rely on simplified interpretations of nutrition science. Although some may produce short-term weight loss, many lack rigorous scientific support and may be nutritionally imbalanced or difficult to sustain. The recurring popularity of fad diets reflects enduring public interest in weight control, physical appearance, and quick solutions to complex health and nutritional issues.

Historical perspectives

Fad diets have existed for centuries, evolving alongside changing ideas about health, nutrition, and body image. One of the earliest examples emerged in the 16th century, when Venetian nobleman Luigi Cornaro promoted the benefits of a restricted diet in La Vita Sobria (The Art of Living Long), a series of essays describing his personal experiences of cutting certain foods from his diet. In the 19th century, English undertaker William Banting promoted a low-carbohydrate eating plan for weight loss. By the mid-to-late-20th century, mass media helped popularize diets that promised rapid results through calorie restriction or highly specific food choices, such as the grapefruit diet and cabbage soup diet. Over time fad diets became a major commercial industry fueled by best-selling books, celebrity endorsements, and social media.

Common features and popular examples

Assortment of protein-rich foods on a wooden table, including salmon, beef, chicken breast, eggs, milk, cheese, beans, and almonds.
High-protein foodsCertain fad diets focus on the consumption of protein. An example is the carnivore diet, which consists of meat, seafood, and eggs, with variations that allow dairy products such as milk, butter, and cheese.

Eating plans such as the Atkins, Paleo (paleolithic), and ketogenic (keto) diets gained popularity by offering simplified explanations for weight loss and challenging conventional nutritional advice. Although the details of these diets vary, most share certain features, including restrictive eating patterns, dramatic health claims, and promises of quick transformation. Many eliminate entire food groups, sharply limit calories, or emphasize specific foods believed to possess unusual health benefits. These diets often rely on simplified explanations of nutrition and metabolism, presenting weight loss as the result of avoiding a single ingredient or following a highly structured regimen. Although some fad diets may produce short-term results, many are difficult to maintain and may lack balanced nutrition or strong scientific support.

Examples of Popular Fad Diets
  • The Atkins diet emphasizes low carbohydrate intake and high protein consumption.
  • The ketogenic (keto) diet severely restricts carbohydrates to promote fat metabolism through ketosis.
  • The Paleo (paleolithic) diet encourages the consumption of foods presumed to resemble those eaten by prehistoric hunter-gatherers.
  • The grapefruit diet centers on grapefruit consumption as a supposed aid to weight loss.
  • The cabbage soup diet relies heavily on low-calorie cabbage soup for short-term weight reduction.
  • Juice cleanses and detox diets promote liquid diets or fasting regimens claiming to “cleanse” the body of toxins.
  • Liquid diets replace meals with shakes, soups, or beverages to sharply reduce calorie intake.
  • The South Beach diet limits certain carbohydrates and fats in phases.
  • The carnivore diet consists almost entirely of animal-based foods.
  • The raw food diet emphasizes eating uncooked and minimally processed foods.

Scientific evaluation, health risks, and medical perspectives

Scientific evaluation of fad diets has produced mixed findings. Many fad diets can lead to short-term weight loss, particularly because they reduce overall calorie intake, limit food choices, or encourage increased attention to eating habits. Some diets, including certain low-carbohydrate and Mediterranean-style approaches, have also shown benefits for specific health markers, such as blood sugar levels and cardiovascular disease risk, in some individuals.

Nonetheless, nutrition experts and medical organizations often express concern about fad diets that severely restrict calories or eliminate major food groups, since such approaches may lead to nutrient deficiencies or other health risks if followed for extended periods. Such diets can increase the risk of nutrient deficiencies, fatigue, dehydration, digestive problems, and loss of muscle mass. Some highly restrictive diets have also been associated with disordered eating behaviors and psychological stress related to food and body image. Scientific studies also have found that many people regain lost weight after discontinuing highly restrictive diets, a pattern sometimes referred to as weight cycling or “yo-yo dieting.”

Medical and public health authorities generally emphasize that no single diet is appropriate for all individuals and that long-term health is more strongly associated with balanced, sustainable eating habits than with short-term dieting trends. Organizations such as the World Health Organization (WHO), the U.S. Centers for Disease Control and Prevention (CDC), and national nutrition agencies typically recommend dietary patterns that include a variety of foods, adequate nutrient intake, and regular physical activity. Some eating plans often labeled as fad diets may contain scientifically supported elements, but experts caution that exaggerated health claims and oversimplified nutritional advice can mislead consumers and obscure the complex factors involved in weight management and overall health.

Kara Rogers