Nutritional decisions may be important for health, and yet identifying trustworthy sources of advice can be difficult to achieve. Many people turn to books for nutritional advice, making the contents of these books and the expertise of their authors relevant to public health. Here, the top 100 best-selling books were identified and assessed for both the claims they make in their summaries and the credentials of the authors.
Weight loss was a common theme in the summaries of nutritional best-selling books. In addition to weight loss, 31 of the books promised to cure or prevent a host of diseases, including diabetes, heart disease, cancer, and dementia; however, the nutritional advice given to achieve these outcomes varied widely in terms of which types of foods should be consumed or avoided and this information was often contradictory between books. Recommendations regarding the consumption of carbohydrates, dairy, proteins, and fat in particular differed greatly between books.
To determine the qualifications of each author in making nutritional claims, the highest earned degree and listed occupations of each author was researched and analyzed. Out of 83 unique authors, 33 had an M.D. or Ph.D degree. Twenty-eight of the authors were physicians, three were dietitians, and other authors held a wide range of jobs, including personal trainers, bloggers, and actors. Of 20 authors who had or claimed university affiliations, seven had a current university appointment that could be verified online in university directories.
The 100 summaries of best-selling books showed very little consistency in terms of what were the key components of diet that would achieve all these benefits. Many summaries included strong views surrounding the consumption of carbohydrates, as six summaries suggested a low or no carb diet and six suggest being gluten or grain free. However, four summaries did support eating grains or bread and one suggested a high-carb diet.
Given the large, almost wild, diversity in nutritional opinions and claims, it may be difficult to set a threshold of what would qualify as disputable and unsubsantiated versus not. Regardless, many claims seemed very puzzling to us and based on our knowledge of the scientific literature we would not be able to even remotely endorse them.