Science, advocacy, and quackery in nutritional books: an analysis of conflicting advice and purported claims of nutritional best-sellers

The paper investigates the trustworthiness and scientific grounding of nutritional advice disseminated through best-selling books. Given that optimal dietary composition remains uncertain and U.S. Dietary Guidelines are periodically updated amid contested evidence, individuals often turn to diverse information sources of varying credibility. Surveys indicate comparable reliance on family/friends and healthcare professionals for nutrition information, and substantial reliance on media sources. Misinformed beliefs can become entrenched. The study aims to evaluate the educational and occupational credentials of best-selling nutrition book authors and to analyze the range and nature of health claims and dietary recommendations made in their book summaries.

Background elements referenced include: the contested nature of evidence informing U.S. Dietary Guidelines and calls for reform in nutritional epidemiology; consumer information-seeking patterns showing reliance on non-expert sources; and prior work on the persistence of nutritional myths. The paper also references critiques of specific popular diets and commentary on emerging, controversial areas such as functional medicine.

Data source and selection: Using sales pattern data for bestsellers (Yucesoy et al., 2018), the authors focused on the Health and Fitness category aimed at nonprofessionals. From top sellers during 2008–2015, they screened Google Books summaries to identify books primarily focused on nutrition advice. Exclusions: 47 books on pregnancy, exercise, beauty, or fashion; 8 recipe/reference books lacking advice; and 59 multi-theme books not exclusively about nutrition. For books with multiple editions in the list, only the top-selling edition was counted. The final sample comprised 100 nutrition-focused bestsellers (among the top 227), with sales ranging from 23,228 to 730,901 (median 55,735). Author credentials: For each of 83 unique authors, online searches (15–27 October 2018) gathered educational and occupational information from biographies, interviews, news, Wikipedia, and Google Books. For authors with claimed university affiliations, Google Scholar searches (1–22 November 2018) recorded publications with ≥100 citations (research, reviews, opinion pieces). Claimed faculty appointments were verified via university directories where possible. Content extraction from summaries: From Google Books summaries, the study extracted program length (days), claimed weight loss (pounds), claims on increasing lifespan or energy, and disease prevention/treatment claims (with specific diseases). Key nutritional recommendations were recorded (diet types; food classes to consume/avoid). Text-mining: The full text of seven of the top ten best-selling books (three not available electronically) was searched for the terms “systematic review”, “meta-analysis”, and “randomiz(s)ed” in the context of controlled/clinical trials to gauge engagement with evidence-based medicine.

Author qualifications and occupations: Among 83 unique authors, 33.7% had an M.D., 6.0% had a Ph.D., and about half had no M.D., Ph.D., or other graduate degree. Twenty-eight authors were physicians; three were dietitians. Other occupations included editors, entrepreneurs, personal trainers, nutritionists, actors, bloggers, reality TV stars, a firefighter, and a professional pool player. Purported benefits: Of 100 book summaries, 80 mentioned weight loss/management. Among summaries specifying program length and/or weight loss, the median program length was 21 days (n=45; IQR 14–30) and median weight loss was 15.5 pounds (n=20; IQR 10–20). Thirty-one summaries claimed the diet could cure or prevent disease. Most frequently listed: diabetes (n=15), heart disease (n=12), cancer (n=11), dementia (n=8), arthritis (n=6), autoimmune disorders (n=5), Parkinson’s disease (n=3), autism spectrum disorder (n=3), and depression (n=3). Additional claims: increased energy (n=13) and increased lifespan (n=7). Incongruent recommendations: Carbohydrates: 6 suggested low/no-carb; 6 suggested gluten/grain-free; 4 supported eating grains/bread; 1 suggested a high-carb diet. Dairy: 2 advised avoiding dairy; 3 advised consuming dairy (2 preferring non/low-fat; 1 preferring full-fat). Emphasis: high-plant (n=9), high-fat (n=7), high-protein (n=4). Popular diet endorsements: Mediterranean (n=4), paleo (n=3), ketogenic (n=2). Meal replacements: smoothies (n=5), bone broth (n=2). Alternating strategies to affect metabolism (n=3). Other suggestions: anti-inflammatory foods (n=3), reduce processed foods (n=6), reduce/replace sugar (n=8), nutrient-dense foods (n=3), vegetarian (n=3), whole foods (n=5), low glycemic index (n=2). Calories/portions: 1 summary suggested counting calories; 8 advised not counting. 1 suggested reducing portions/calories; 4 advised not to reduce; 3 suggested cycling portion/calorie size; 2 encouraged eating more. University affiliations and scholarship: Of 83 authors, 20 had some mention of a faculty appointment (current or past); 7 had current appointments validated via institutional websites. Many roles were adjunct/voluntary; most professors were in biomedical fields; one in non-fiction writing. Fifteen of the 20 had at least one ≥100-citation publication as first/last author (often opinion pieces). Concerns and controversies: One university-affiliated author (Aggarwal) had 28 retractions, 10 expressions of concern, and 17 corrections (as of Jan 9, 2020). Some authors were listed by watchdogs or faced scientific criticism (e.g., Perlmutter, Agatston, Davis). Text-mining of full texts: Of seven analyzed top-selling books, one referenced meta-analyses (“The 20/20 Diet”); three referenced randomized controlled/clinical trials (“Master Your Metabolism”, “Flat Belly Diet!”, “The 20/20 Diet”), with only “The 20/20 Diet” citing more than five. Most appearances of search terms (25/28) were in reference lists. Two books (“Master Your Metabolism” and “The 20/20 Diet”) lacked in-text citations, obscuring linkage between claims and studies.

The analysis shows that best-selling nutrition books frequently make strong health claims, including disease prevention/treatment and weight loss, yet offer highly inconsistent and often contradictory dietary recommendations. Author credentials are mixed, with many lacking advanced degrees in relevant fields and few holding verifiable university appointments. Engagement with rigorous evidence (systematic reviews, meta-analyses, randomized trials) appears limited, and citation practices often do not transparently connect claims to studies. Given that consumers often rely on such sources, these findings highlight potential public health risks from misinformation and underscore the need for improved communication about evidence quality, author qualifications, and conflicts of interest. Regulatory frameworks offer limited oversight for such publications. The prominence of commercialization and potential financial incentives around diet brands and associated products further complicates trust. Broader awareness and mechanisms to promote evidence-based guidance are needed to protect public understanding and health decisions.

This study systematically examined the claims and author credentials of the top 100 nutrition-focused best-selling books. It documents frequent, sometimes expansive health promises alongside profound inconsistency in dietary advice and limited engagement with evidence-based medicine. Author qualifications vary widely, with few verifiable academic appointments and notable controversies among some highly visible authors. The findings suggest that a substantial portion of best-selling nutrition literature likely contains misinformation and that it may influence public behavior more than peer-reviewed science. Future research should: (1) qualitatively analyze full texts to assess evidence use, reasoning, and accuracy; (2) investigate dissemination and influence across newer media (blogs, social media) and devise oversight/accountability mechanisms; (3) study how diet information shapes cultural identity and choices; and (4) enhance transparency regarding financial interests tied to diet books and related products.

Analyses primarily used Google Books summaries, which may not accurately represent complete book content and may selectively emphasize aspects. Authorship of summaries is unclear. Only primary authors were assessed for credentials; contributions by co-authors or consulted experts within books may have been missed. Full-text evidence assessment was limited to seven of the top ten books and only via keyword searches for specific evidence-related terms, potentially missing other forms of support or scientific argumentation. The study period and bestseller dataset (2008–2015) may not reflect newer trends or publications.