Intended for healthcare professionals


Implausible results in human nutrition research

BMJ 2013; 347 doi: (Published 14 November 2013) Cite this as: BMJ 2013;347:f6698
  1. John P A Ioannidis, professor of medicine, health research and policy, and statistics
  1. 1Stanford Prevention Research Center, Stanford, CA 94305, USA
  1. jioannid{at}

Definitive solutions won’t come from another million observational papers or small randomized trials

Research into human nutrition has been criticized on numerous occasions. Critics have focused on the poor track record of observational claims when tested in subsequent randomized trials (0/52 success rate in one review) and perpetuated fallacies.1 2 3 In contrast to major nutritional deficiencies and extreme cases, the effects of modest differences in nutrient intake have been difficult to study reliably at the population level. Nonetheless, some results, even of randomized trials, have been extremely promising.4 5 However, to establish a less controversial legacy for this important field, we should avoid past traps and be explicit about reasonable expectations. Implausible results that are “too good to be true” still threaten nutritional research on many fronts, including survey measurements, observational associations, treatment effects in randomized trials, and estimates of the impact on populations.

Nutritional intake is notoriously difficult to capture with the questionnaire methods used by most studies. A recent analysis showed that in the National Health and Nutrition Examination Survey, an otherwise superb study, for two thirds of the participants the energy intake measures inferred from the questionnaire are incompatible with life.6 More sophisticated measurements based on biochemical, web, camera, mobile, …

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