Intended for healthcare professionals

CCBYNC Open access

Rapid response to:


Effects of a low carbohydrate diet on energy expenditure during weight loss maintenance: randomized trial

BMJ 2018; 363 doi: (Published 14 November 2018) Cite this as: BMJ 2018;363:k4583

Rapid Response:

Resolving the conflict between science and ethics in nutrition research

Scientific debates in nutrition may sometimes proceed along predictable lines, seemingly influenced by personal ethical views. Advocates of vegan diets tend to emphasize studies showing the benefits of consuming carbohydrate over fat, perhaps because virtually all dietary carbohydrates come from plants. (In a previous post, we responded to criticism of our study by 2 individuals with leadership roles in Physicians Committee for Responsible Medicine, a group that discourages use of animals for food and medical research (1).)

Conversely, advocates of low-carbohydrate diets commonly highlight the advantages of animal products, perhaps because meat, eggs and dairy products were historically primary sources of dietary fat.

However, these implicit biases do not reflect the reality of the modern food environment. One can easily consume a low-fat, animal-based diet with foods such as chicken breast, lean beef, egg whites, and low-fat cheese.

Alternatively, a low-carbohydrate diet can be based on high-fat plant foods including nuts, seeds, olive oil, avocado, coconut oil and dark chocolate – as exemplified by several recent popular books and a large social media group (2) that recommend a vegan ketogenic diet.

To find common ground, we must carefully distinguish scientific from ethical considerations. But with the abundant choice of foods now available for most people in developed countries, all sides of the diet debates can take comfort that scientific truth and the pursuit of an ethical lifestyle need not be in conflict.

1. Authors' response to Kahleova, Katz and Barnard.

2. Facebook Group, Vegan Keto Made Simple.

Competing interests: As detailed in the manuscript

26 November 2018
David S. Ludwig
Physician Scientist
Cara B. Ebbeling
Boston Children's Hospital
300 Longwood Ave, Boston MA 02115 (USA)