Development and Evaluation of a Sham Diet Intended as a Placebo-Control Diet for Food-Based Interventional Trials in...

The "gold standard" for successful blinding in controlled food-based dietary interventional trials includes a sham diet.

This study aimed to develop and evaluate a sham diet intended for use as a comparator in ulcerative colitis dietary trials.

A sham diet to the experimental 4 Strategies to SUlfide REduction (4-SURE) diet was systematically constructed using a 6-step process. Health care professionals naïve to the sham and 4-SURE diet were surveyed to evaluate the impression of the sham diet as an intervention. Healthy adult volunteers then received dietary education and implemented the sham diet for 7 days to evaluate blinding.

Twenty-two health professionals were recruited from the hospital and research institute in Adelaide, South Australia, from September to October 2020 to complete the survey. Twenty health professionals met the eligibility criteria and completed the survey. Twenty-five healthy adults were recruited via advertisements on notice boards and email distribution lists at the hospital and a university in Adelaide, South Australia, from March through June 2021 to complete the 7-day diet trial. Twelve healthy adults met eligibility requirements, agreed to participate, and completed the 7-day trial.

The combined primary outcome was the believability that the sham diet could be an intervention diet and the success of blinding by asking whether the diet was designed to be an intervention or placebo for ulcerative colitis trials. Secondary outcomes included acceptability and tolerability (visual analog scales), adherence, nutrient intake, and dietary education.

Descriptive data are presented as mean (95% confidence interval [CI]) or median (interquartile ranges [IQR]) for continuous variables. T-tests were used to compare the meal plans and trial time points.

Of 20 health care professionals surveyed, 19 (95%) agreed both diets impressed a similar complexity, and 15 of 20 (75%) agreed both set meal plans gave the impression of therapeutic dietary prescriptions. Eight (40%) correctly identified the 4-SURE diet. Twelve adults, 10 women and 2 men, completed the sham diet trial. Blinding was successful. All believed the diet could be the intervention diet. The diet was highly tolerable (mean, 83 mm; 95% CI, 75, 92 mm). The nutrient composition of volunteers' diets remained uniformly unchanged between baseline and 7 days.

This sham diet is credible as a therapeutic dietary prescription. It was highly tolerable, did not alter nutrients of therapeutic interest to the 4-SURE diet, and was suitable to deploy in food-based trials for ulcerative colitis as a control to diets with a similar dietary scaffold.