The challenges of control groups, placebos and blinding in clinical trials of dietary interventions

Proc Nutr Soc. 2017 Aug;76(3):203-212. doi: 10.1017/S0029665117000350. Epub 2017 Jun 20.


High-quality placebo-controlled evidence for food, nutrient or dietary advice interventions is vital for verifying the role of diet in optimising health or for the management of disease. This could be argued to be especially important where the benefits of dietary intervention are coupled with potential risks such as compromising nutrient intake, particularly in the case of exclusion diets. The objective of the present paper is to explore the challenges associated with clinical trials in dietary research, review the types of controls used and present the advantages and disadvantages of each, including issues regarding placebos and blinding. Placebo-controlled trials in nutrient interventions are relatively straightforward, as in general placebos can be easily produced. However, the challenges associated with conducting placebo-controlled food interventions and dietary advice interventions are protean, and this has led to a paucity of placebo-controlled food and dietary advice trials compared with drug trials. This review appraises the types of controls used in dietary intervention trials and provides recommendations and nine essential criteria for the design and development of sham diets for use in studies evaluating the effect of dietary advice, along with practical guidance regarding their evaluation. The rationale for these criteria predominantly relate to avoiding altering the outcome of interest in those delivered the sham intervention in these types of studies, while not compromising blinding.

Keywords: IBS irritable bowel syndrome; Clinical trial; Controls; Dietary intervention; Placebo; Research design.

Publication types

  • Review
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biomedical Research / education
  • Biomedical Research / methods
  • Biomedical Research / trends
  • Congresses as Topic
  • Diet Therapy / adverse effects
  • Diet Therapy / methods*
  • Diet Therapy / trends
  • Double-Blind Method
  • Guidelines as Topic
  • Humans
  • Nutritional Sciences / education
  • Nutritional Sciences / methods
  • Nutritional Sciences / trends
  • Patient Education as Topic
  • Placebos
  • Randomized Controlled Trials as Topic* / standards
  • Research Design / standards
  • Research Design / trends
  • Single-Blind Method
  • Societies, Scientific


  • Placebos