(P38-08-26) Measuring Ad Libitum Energy Intake in Controlled Metabolic Feeding Studies: Is There a More Efficient Way?

Objectives: Ad libitum controlled feeding studies are time-consuming and labor-intensive. This secondary analysis examined the accuracy and precision of simply measuring the total weight of the leftover meal (simplified method; SM) compared to weighing back each individual food item remaining in the meal (conventional method; CM) to improve efficiency.

Methods: SM and CM weighbacks were completed across two inpatient randomized controlled trials with four different diets (minimally processed (MP), ultra-processed (UP), low-carbohydrate (LC) and low-fat (LF)) consumed ad libitum for two-weeks each. Twenty adults participated in each study. Differences, correlation and agreement in energy and macronutrient intake between SM and CM were examined by diet, day, meal and for each macronutrient.

Results: Across a total of 3341 meals (767 ± 351 kcal/meal), the difference between SM and CM was 9.5 ± 104.4 kcal (p < 0.001). The dinner meal (24 ± 128 kcal) and calories from protein (28 ± 54 kcal) were the main drivers of the overall difference between methods. The correlation between total kcal consumed between the two methods was strong overall (r = 0.98, P < 0.001) and within each diet (all r ≥ 0.94, P < 0.001). There was high agreement between the two methods for all diets (mean biases < 60 kcal/day), however, a significant linear bias (0.09 ± 0.02, P < 0.001) was observed in the MP diet and the magnitude of this bias produced 9 kcal of deviation for every 100 kcal increase in energy intake.

Conclusions: SM is a viable alternative to CM in ad libitum controlled feeding studies measuring energy intake across 2 weeks, however, the magnitude bias for the MP diet should be investigated further. Incorporation of SM would greatly improve implementation constraints and allow for more efficient completion of studies investigating ad libitum energy intake without compromising data integrity.

Funding Sources: This research was supported by the Intramural Research Program of the National Institute of Diabetes and Digestive and Kidney Diseases within the National Institutes of Health.