Fad Diets: A Review ★☆☆☆☆

By R.Davies, PhD・Diet Atlas
Published June 08, 2026 | 3 min read

Fad diets represent a broad category of diets that are generally severe, restrictive and unproven. They often promise rapid weight loss or dramatic health changes. Unlike evidence-based diets developed through scientific research, fad diets typically emerge from commercial interests, celebrity endorsements, or pseudoscientific theories. They gain popularity through sensational marketing claims, or sometimes just marketing (without any specific health claims).

Fad diets share a few common features:

• Severely restricted caloric intake (often under 1,000 calories a day)

• Elimination of entire food groups

• Reliance on single foods or food combinations

• Rigid rules without flexibility

• Promises of rapid results

• Claims related to ‘detoxification’ or miracle cures for fashionable disorders

Examples include very low-calorie diets, ‘mono-diets’ (eating only one type of food like grapefruit or cabbage soup), and elimination diets that remove multiple food groups at once; there are also extreme versions of legitimate diets (e.g., ultra-low-carb, ultra-low-fat, ultra-long fasts).

The appeal of fad diets usually stems from desperation, as they promise quick solutions for people who are frustrated with diets that take longer to see measurable results. Fad diets use persuasive marketing exploiting body image concerns, biased testimonials, before-and-after photos, cultural obsession with body image and rapid transformations or glow-ups. Social media has increased exposure to fad diets, particularly among young adults and adolescents who are more vulnerable to the marketing.

Pros

Fad diets' only real ‘benefit’ is the potential of rapid initial weight loss, which is only really beneficial for a small group of people under specific circumstances. This can provide immediate psychological gratification and visible results very quickly. 

The dramatic change on the scales may create motivation and a sense of accomplishment for those who struggle to control their weight. However, the initial rapid weight loss is largely water and “glycogen” (stored carbohydrate), with some fat and muscle loss.

In rare medical situations, medically supervised very low-calorie diets can be used to treat specific health conditions. The rigid structure and elimination of decision-making can also appeal to some people. The clear rules about what's ‘allowed’ and what’s ‘forbidden’ remove any uncertainty. For some people, this may feel psychologically simpler compared to more flexible, balanced diets, which require ongoing judgments, decision-making and moderation.

Cons

Severe restriction of calories and entire food groups creates deficiencies of essential vitamins, minerals, protein, healthy fats, and dietary fibre. Different types of fad diets will naturally create different nutrient deficiencies. Ultra-low-carb diets increase the chances of fibre and certain micronutrient deficiencies. Ultra-low-fat diets reduce fat-soluble vitamins and essential fatty acids. Ultra-low-calorie diets risk widespread micronutrient deficiencies and inadequate protein intake.

Most extreme fad dieters regain lost weight within months, often exceeding their starting weight (‘yoyo dieting’). Some research suggests yoyo-dieting may worsen your health, lead to weight gain, and make weight loss more difficult (along with increased risk of developing eating disorders). Immediate safety concerns include muscle wasting, fatigue, weakness, hair loss, amenorrhoea (i.e., loss of, or irregular, menstrual cycle), gallstones, loss of bone density, anaemia, impaired immunity, and heart problems.

Sustainability of these diets is also poor, with most people abandoning them within weeks to months. Hunger, monotony, social barriers, the inability to participate in normal eating situations, the cost of specialised foods or programs, and the psychological burden of rigid restriction all affect adherence.

Bottom Line

Most fad diets offer temporary weight loss at a high cost. Nutrient deficiency, muscle wasting, metabolic health, psychological harm, and eating disorders are risks. For most people, fad diets have poor long-term outcomes, poor adherence rates, and notable safety concerns. They’re not advised for general use, if at all.

Sources

Ashtary-Larky D et al. Rapid Weight Loss vs. Slow Weight Loss: Which is More Effective on Body Composition and Metabolic Risk Factors? Int J Endocrinol Metab. 2017 May 17;15(3):e13249. PMID: 29201070

Fothergill E et al. Persistent metabolic adaptation 6 years after "The Biggest Loser" competition. Obesity (Silver Spring). 2016 Aug;24(8):1612-9. PMID: 27136388

Montani JP et al. Dieting and weight cycling as risk factors for cardiometabolic diseases: who is really at risk? Obes Rev. 2015 Feb;16 Suppl 1:7-18. PMID: 25614199

Pacanowski CR et al; Look AHEAD Research Group. Psychological status and weight variability over eight years: Results from Look AHEAD. Health Psychol. 2018 Mar;37(3):238-246. PMID: 29504788

Scragg J et al. Feasibility of a Very Low Calorie Diet to Achieve a Sustainable 10% Weight Loss in Patients With Nonalcoholic Fatty Liver Disease. Clin Transl Gastroenterol. 2020 Sep;11(9):e00231. PMID: 33094956

Steven S et al. Very Low-Calorie Diet and 6 Months of Weight Stability in Type 2 Diabetes: Pathophysiological Changes in Responders and Nonresponders. Diabetes Care. 2016 May;39(5):808-15. PMID: 27002059

Tahreem A et al. Fad Diets: Facts and Fiction. Front Nutr. 2022 Jul 5;9:960922. PMID: 35866077

Further Reading

Atkins Diet: A Review

Low-Fat Diets: A Review

Mediterranean Diet: A Review

Published: June 08, 2026

Lead Author: R.Davies, PhD, MRes, BSc, CPT, FHEA | Author Bio
Dr Davies is a physiologist specialising in human health, performance and nutrition.

Alphabet Guides provides independent, evidence-based information you can trust. Learn more about our Editorial Standards.

Disclaimer: The information on this website is for educational purposes only. It should not be used as a substitute for medical advice from a qualified healthcare professional.