Challenges in Designing and Delivering Diets and Assessing Adherence: A Randomized Controlled Trial Evaluating the 2010 Dietary Guidelines for Americans

Abstract

Background: Controlled-feeding trials are challenging to design and administer in a free-living setting. There is a need to share methods and best practices for diet design, delivery, and standard adherence metrics.

Objectives: This report describes menu planning, implementing, and monitoring of controlled diets for an 8-wk free-living trial comparing a diet pattern based on the Dietary Guidelines for Americans (DGA) and a more typical American diet (TAD) pattern based on NHANES 2009-2010. The objectives were to 1) provide meals that were acceptable, portable, and simple to assemble at home; 2) blind the intervention diets to the greatest extent possible; and 3) use tools measuring adherence to determine the success of the planned and implemented menu.

Methods: Menus were blinded by placing similar dishes on the 2 intervention diets but changing recipes. Adherence was monitored using daily food checklists, a real-time dashboard of scores from daily checklists, weigh-backs of containers returned, and 24-h urinary nitrogen recoveries. Proximate analyses of diet composites were used to compare the macronutrient composition of the composite and planned menu.

Results: Meeting nutrient intake recommendations while scaling menus for individual energy intake amounts and food portions was most challenging for vitamins D and E, the sodium-to-potassium ratio, dietary fiber, and fatty acid composition. Dietary adherence for provided foods was >95%, with no differences between groups. Urinary nitrogen recoveries were ∼80% relative to nitrogen intake and not different between groups. Composite proximate analysis matched the plan for dietary fat, protein, and carbohydrates. Dietary fiber was ∼2.5 g higher in the TAD composite compared with the planned menu, but ∼7.4 g lower than the DGA composite.

Conclusions: Both DGA and TAD diets were acceptable to most participants. This conclusion was supported by self-reported consumption, quantitative weigh-backs of provided food, and urinary nitrogen recovery. Dietary adherence measures in controlled-feeding trials would benefit from standard protocols to promote uniformity across studies. The trial is registered at clinicaltrials.gov as NCT02298725.

Keywords: blinding diet interventions; controlled feeding; diet acceptability; diet patterns; dietary adherence; free-living trial; menu design.

Published by Oxford University Press on behalf of the American Society for Nutrition 2020.

Figures

FIGURE 1

The left panel is a graphical representation of the USDA Food Patterns table (13) for the recommended food groups and their intake amounts across different calorie levels, presented as a percentage of the 2000-kcal pattern. The right panel is the proportionately scaled version of the 2000-kcal pattern used to design the DGA menu in the current study. DGA, Dietary Guidelines for Americans; SoFAS, solid fats and added sugars.

FIGURE 2

Scores from the Diet Acceptability Questionnaire for food groups for the TAD (n = 22) and DGA (n = 22) interventions in women. The pairs of bars, reading from left to right on each graph, represent the number of participants who strongly agreed, agreed, were neutral, disagreed, or strong disagreed; red bars depict the TAD group, blue bars depict the DGA group. No significant differences between the interventions were identified. DGA, Dietary Guidelines for Americans; TAD, typical American diet.

FIGURE 3

Dietary nitrogen intake and urinary nitrogen excretion in women consuming diets based on the the TAD or DGA diet. The solid bars represent the mean dietary nitrogen intake representing the respective intervention diets provided during the 8-wk study. The hatched bars represent the mean urinary nitrogen excretion measured from three 24-h urine collections taken at week 1, week 4, and week 7 of the intervention. The error bars represent the SEM. The percentage recovery (mean ± SEM) of dietary nitrogen recovered in the urine was 81.9 ± 4.0% for TAD and 76.9 ± 3.6% for DGA. DGA, Dietary Guidelines for Americans; TAD, typical American diet.