Abstract & Commentary

Popular Diets for Weight Loss

By Dónal P. O’Mathúna, PhD, and Catrina Feeney, Dr. O’Mathúna is Senior Lecturer in Ethics, Decision-Making & Evidence, School of Nursing and Human Sciences, Dublin City University, Ireland; and Ms. Feeney is a Student Dietician, The Ohio State University, Columbus, Ohio. Dr. O’Mathúna and Ms. Feeney report no financial relationships relevant to this field of study.

With the beginning of another year, many will be resolving to lose some weight. According to consumer surveys conducted for industries manufacturing low-calorie foods and beverages, 54% of Americans were trying to lose weight in 2010, up from 33% in 2004 and 24% in 2000.1 The U.S. market for all weight loss products and services is now worth $60.9 billion.2

This article will examine some of the popular diets currently being promoted. A future article will examine diets to be reviewed in a soon-to-be-released Consumer Reports article. Space does not permit a review of all commonly used diets, so only a few popular ones will be selected. Other diets have been reviewed here more recently, including high-protein, low-carbohydrate diets3 and the human chorionic gonadotropin (HCG) diet.4 The diets examined here illustrate the variety of strategies being advocated, and the varying degrees to which these are based on healthy nutrition principles. Different organizations warn against diets promoted on the basis of certain traits, some of which have been compiled in Table 1.

Table 1. Warning Signs in the Promotional Materials for Popular Diets


Weight loss programs based on inaccurate principles rarely achieve successful weight loss, especially in the longer term. This leads people to either attempt other ineffective programs or become defeated and gain more weight. Harm can also occur if a diet encourages nutritionally unsound practices, leads to too rapid weight loss, or leads to the neglect of essential nutrients. Given how many Americans are currently trying to lose weight, and how important this is for health, health care professionals should be able to help patients evaluate popular diets and identify those based on the best available evidence.

Alkaline Diet

The alkaline diet is primarily a plant-based diet. Fresh vegetables and fruit are prioritized, along with foods that produce more alkaline urine. Dairy products, meats, eggs, and some nuts produce more acidic urine and are discouraged, as are more processed foods, white flour, white sugar, and caffeine. Some promoters of the alkaline diet claim that it lowers the blood pH that overcomes unhealthy acidity in the body. This is said to lead to weight loss, and treatment of arthritis, diabetes, and cancer.

Scientific Evaluation. Different tissues in the body have different pH values (ranging from 1.3-3.5 in the stomach to 8.8 in pancreatic fluid).5 The pH of urine varies between 4.6 and 8.0, and this is influenced by diet. More alkaline foods can reduce the risk of kidney stones, but the only relevant article found in PubMed identified no evidence to support the claims made for the alkaline diet other than those due to increased consumption of plant foods.5 This review did not address the alkaline diet’s effectiveness regarding weight loss.

Concerns and Recommendations. The alkaline diet has beneficial aspects, particularly in promoting consumption of fruits and vegetables. If these replace other high-calorie foods, weight loss may result. However, this has nothing to do with changing the body’s pH. The alkaline diet can lead to insufficient protein due to meat restrictions, and insufficient calcium, due to dairy restrictions. People on the alkaline diet should ensure they obtain sufficient essential nutrients.

Grapefruit Diet

Grapefruit first appeared in fad diets in the 1930s Hollywood Diet, a forerunner of the unofficial Mayo Clinic Diet. This recommended eating grapefruit before every meal for 12 days, and restricted total consumption to 800-1000 calories daily.6 The claim is made that grapefruit stimulates enzymes in the body that metabolize fat. The diet has many variations, but a similar pattern of fresh grapefruit before meals of primarily low-calorie foods. Promises of losing 10 pounds in 12 days are commonplace.

Scientific Evaluation. Grapefruit has been the subject of some research encouraged by the citrus growing industry. Several compounds have been isolated and shown to have beneficial cardiovascular effects in animals.6 A few human trials have produced conflicting results, with these effects continuing to be investigated.

For weight loss, a few clinical trials have been published recently. Ninety-one obese patients were randomized to either half a grapefruit, grapefruit juice, grapefruit extract capsules, or an equivalent placebo taken three times daily before meals.7 Over 12 weeks, the fresh grapefruit group lost 1.6 kg, the grapefruit juice group lost 1.5 kg, the grapefruit capsule group lost 1.1 kg, and the placebo group lost 0.3 kg. The differences were significant (P < 0.05). In another trial, 85 obese adults were randomized to consume 127 g of either fresh grapefruit, grapefruit juice, or water before three daily meals (called a preload).8 Individual daily energy expenditure was calculated and meals planned to provide 12.5% fewer calories than expended. For the first 2 weeks, everyone followed only the restricted calorie diet, and for the next 10 weeks they followed the diet plus the different preloads. Average weight loss of 1 kg occurred during the first 2 weeks, with this increasing by 13.3% (P < 0.0001) during the preload phase. Average overall weight loss was 7%. However, no significant differences in weight loss or body fat composition existed between the three groups.

The most recent study randomly assigned 74 overweight and obese adults to those who consumed half a fresh grapefruit before meals for 6 weeks or a control group.6 All subjects consumed their usual diet except they eliminated selected fruit and vegetables containing similar polyphenols to grapefruit. No statistically significant differences in body weight, body composition, or lipid profile were found between the two groups.

Concerns and Recommendations. Grapefruit is a nutritious food that is being shown to have some health benefits. However, the approach taken in the grapefruit diet has not been shown to be effective, except by way of restricting caloric intake. Although grapefruit is nutritious, concerns have been raised about potential drug interactions. Grapefruit can lead to elevated blood levels of statins, but a daily grapefruit or glass of grapefruit juice does not lead to clinically significant changes.9 Consuming large amounts of grapefruit could have more significant effects and should be avoided in those taking statins, and numerous other medications including specific antiarrhythmics, calcium channel blockers, and immunosuppressants.10

Paleo Diet

The Paleo (or Paleolithic) diet claims to be the world’s healthiest diet based on the foods that our hunter-gatherer ancestors would have eaten during the Stone Age. In the last several thousand years, humans have evolved little, but our diets have changed dramatically and so have the diseases we experience.11 The introduction of cereal grains, dairy products, refined sugar, and processed fats are said to have created a mismatch between our diet and our genetic adaptation. Therefore, a diet rich in lean meat, seafood, fruits, vegetables, and nuts (the Paleo diet) will be more healthy.12

Scientific Evaluation. Advocates of the Paleo diet note that hunter-gatherer communities have lower incidences of degenerative diseases.13 Markers such as blood pressure, insulin sensitivity, body mass index, and bone health tend to be better than in those consuming typical Western diets. For example, 13 type 2 diabetes patients consumed either a Paleo diet or one based on contemporary dietary guidelines for diabetes.14 After 3 months, participants crossed over to the other diet. Significantly better improvements were found on the Paleo diet for weight loss (-3 kg; P = 0.01), waist circumference (-4 cm; P = 0.02), body mass index (-1; P = 0.04), and other cardiovascular markers. However, the study was terminated early due to difficulties recruiting sufficient subjects to obtain the number determined by a pre-study power calculation. About five other trials with between 9 and 29 subjects found various improvements with the Paleo diet.15 None of these lasted longer than 12 weeks.

Concerns and Recommendations. Twenty popular diets were evaluated by nutrition experts for U.S. News & World Report, with the Paleo diet getting the lowest ranking.16 Concerns were expressed at its high fat content (39%) due to its high protein content (39%). The diet is low in fiber, calcium, vitamin D, and iron.12 It also increases average household food costs by about 10%.12 The underlying evolutionary principles and dietary intakes have been critiqued as implausible and impossible to verify.11 Anthropologists claim that up to 80% of hunter-gatherer diets were plant-based, with much less meat than advocated in the Paleo diet.17 The increased plant consumption in this diet is commendable.

South Beach Diet

The South Beach diet is an adaptation of the high-protein, low-carbohydrate diet popularized as the Atkins diet.18 The goal is to eliminate “bad fats and bad carbohydrates,” which are those metabolized more quickly. The South Beach diet has three phases.19 The first lasts 2 weeks and claims rapid weight-loss of 8 to 13 pounds. It does this by severely restricting specific foods, particularly carbohydrates, sugars, dairy, and alcohol, but also fruit. Phase 2 is for sustained weight loss with an emphasis on consuming lean protein and low-fat dairy, with the gradual introduction of whole-grain carbohydrates and fruit. Phase 3 is for maintaining body weight at the level achieved. It involves expanding the range of plant foods, while promoting consistent meal times, reasonable portion sizes, healthy snacks, and water consumption. In this stage, the South Beach diet encourages similar proportions of protein to the Atkins diet (26% and 29%, respectively), but with less fat (40% and 62%) and more carbohydrates (33% and 9%).20

Scientific Evaluation. The first phase of the South Beach diet has been criticized as overly restrictive. Such approaches may result in weight loss because of how few calories they allow, but can provide less than the minimum recommended 1000 calories per day.7 On the other hand, the South Beach Phases 2 and 3 take advantage of the growing evidence supporting the effectiveness of high-protein, low-carbohydrate diets for weight loss over 6 months and possibly 12 months.3 The quality of Phase 2 South Beach was found to slightly exceed the recommendations of the 2005 USDA Food Guide Pyramid, while Phase 3 was slightly below.19 Evidence for the long-term effectiveness of the South Beach diet is lacking.

Concerns and Recommendations. The South Beach diet has strengths and weaknesses. A systematic evaluation of the nutrition statements in the South Beach book identified 42 different claims.18 Of these, 14 (33%) were supported by peer-reviewed articles, 7 (17%) were not supported by the literature, 18 (43%) were somewhat supported and not supported, and 3 (7%) had no relevant published papers.21 Peer-reviewed articles were not identified to support claims about the diet’s effectiveness, nor how it allegedly leads to weight loss.

During the highly restrictive Phase 1, some people may be encouraged by rapid weight loss, but others may be deterred or defeated by its severity. This phase may lack sufficient calories and essential nutrients. Phases 2 and 3 are much more balanced and provide a structured approach to sustained weight loss and maintenance. However, concerns have been raised about the elevation of some cardiovascular risks when people adhere to high-protein, low-carbohydrate diets for extended periods.3 Further research is needed to investigate these concerns.


A common question is whether eating multiple times during the day increases metabolism and promotes weight loss.22 The answer had been “kept secret” until the 3-Hour Diet promised to take 10 pounds off in 2 weeks by controlling meal times.23 However, 40 years of research have provided no consensus on this, other than that overall daily calorie consumption is more important than how frequently one eats during the day.24

The obesity epidemic has spawned numerous diets, making it important that patients be encouraged to identify and avoid the traits listed in Table 1. Any diet recommending fewer than 1000 calories per day should not be undertaken without medical supervision.25 Evidence-based reviews of new weight loss programs are available from a number of reliable organizations. As well as being able to evaluate popular diets, health care professionals should be aware of the most recent evidence-based dietary guidelines.26 In addition, researchers are starting to systematically evaluate some of the more popular diets, the results of which will help clinicians to better counsel patients about these diets.27


The principles of effective weight loss are uncomplicated, even if easier said than done. The basic principle is to consume fewer calories than are used. For safe, effective, long-lasting weight loss, aim to lose 1-2 pounds per week, which requires consuming 500-1000 calories less than is used each day.25 This may seem like a slow rate of progress, but gradual sustained weight loss will be easier to maintain and allow time for the necessary lifestyle changes — including gradually increased physical activity. How people reduce their calorie intake can be tailored to the individual. Some eliminate high-calorie foods, others prefer replacing certain foods with lower calorie options, some get involved in different calorie-counting programs, while others focus on increasing physical activity. The important thing is to reduce intake and increase output.


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6. Dow CA, et al. The effects of daily consumption of grapefruit on body weight, lipids, and blood pressure in healthy, overweight adults. Metabolism 2012;61:1026-1035.

7. Fujioka K, et al. The effects of grapefruit on weight and insulin resistance: Relationship to the metabolic syndrome. J Med Food 2006;9:49-54.

8. Silver HJ, et al. Effects of grapefruit, grapefruit juice and water preloads on energy balance, weight loss, body composition, and cardiometabolic risk in free-living obese adults. Nutr Metab 2011;8:8.

9. Reddy P, et al. Serum concentrations and clinical effects of atorvastatin in patients taking grapefruit juice daily. Br J Clin Pharmacol 2011;72:434-441.

10. Stump AL, et al. Management of grapefruit-drug interactions. Am Fam Physician 2006;74:605-608.

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12. Metzgar M, et al. The feasibility of a Paleolithic diet for low-income consumers. Nutr Res 2011;31:444-451.

13. Carrera-Bastos P, et al. The Western diet and lifestyle and diseases of civilization. Res Rep Clin Cardiol 2011;2:15-35.

14. Jönsson T, et al. Beneficial effects of a Paleolithic diet on cardiovascular risk factors in type 2 diabetes: A randomized crossover pilot study. Cardiovasc Diabetol 2009;8:35.

15. Klonoff DC. The beneficial effects of a Paleolithic diet on type 2 diabetes and other risk factors for cardiovascular disease. J Diabetes Sci Technol 2009;3:1229-1232.

16. U.S. News & World Report. Best Diets Rankings. Available at: http://health.usnews.com/best-diet. Accessed Jan. 13, 2013.

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18. Agatston A. The South Beach Diet: The Delicious, Doctor-designed, Foolproof plan for Fast and Healthy Weight Loss. New York, NY: Random House; 2003.

19. Ma Y, et al. A dietary quality comparison of popular weight-loss plans. J Am Diet Assoc 2007;107:1786-1791.

20. De Souza RJ. Alternatives for macronutrient intake and chronic disease: A comparison of the OmniHeart diets with popular diets and with dietary recommendations. Am J Clin Nutr 2008;88:1-11.

21. Goff SL, et al. Nutrition and weight loss information in a popular diet book: Is it fact, fiction, or something in between? J Gen Intern Med 2006;21:769-774.

22. Parks EJ, McCrory MA. When to eat and how often? Am J Clin Nutr 2005;81:3-4.

23. Cruise J. The 3-Hour Diet: Lose up to 10 Pounds in Just 2 Weeks by Eating Every 3 Hours! William Morrow Paperbacks; 2006.

24. McCrory MA, et al. Eating frequency and energy regulation in free-living adults consuming self-selected diets. J Nutr 2011;141:148-153.

25. National Institutes of Health. Aim for a Healthy Weight. 2005. Available at: www.nhlbi.nih.gov/health/public/heart/obesity/aim_hwt.pdf. Accessed Jan. 13, 2013.

26. U.S. Department of Agriculture. Dietary Guidelines for Americans, 2010. Available at: www.cnpp.usda.gov/DGAs2010-PolicyDocument.htm. Accessed Jan. 13, 2013.

27. Gardner CD. Low-carbohydrate ketogenic diet and the combination of orlistat with a low-fat diet lead to comparable improvements in weight and blood lipids, but LCKD more beneficial for blood pressure. Evid Based Med 2010;15:91-92.