(LB02-11-24) Fiber’s Utilization for Energy and Life (FUEL): A Randomized, Controlled Feeding Trial Assessing Metabolizable Energy of the Diet With and Without High Fiber Cereal

Objectives: Dietary fiber intake is associated with a lower risk of weight gain and incidence of overweight and obesity. Dietary fibers can impede macronutrient digestibility, reducing dietary metabolizable energy content. Fiber affects the gut microbiota, which directly and indirectly contributes to energy balance. Our primary objective was to evaluate dietary metabolizable energy with and without the inclusion of a high-fiber cereal. We hypothesized that including a high-fiber cereal would reduce the metabolizable energy of the diet.

Methods: Healthy adults (n=19; 12 female, 7 male; mean age 29.9 y; mean BMI 26.2 kg/m²) participated in a double-blind, randomized, controlled, crossover study with two experimental conditions (2 wk each) separated by a 2-wk washout. The study was a fully controlled feeding intervention with the same base diet consumed in each experimental condition; the base diet was supplemented with either three servings/day (282 total kcal) of a low (1g) or high (30 g) fiber cereal. Diets were scaled according to energy requirements such that participants remained weight stable. After a 9-d acclimation period, participants collected all urine and fecal samples produced over 5d (as marked by a Brilliant Blue fecal collection marker). Combustible energy, protein, fat, and total dietary fiber were measured in composite samples of the diet and feces; urine was analyzed for combustible energy and nitrogen. Metabolizable energy and apparent digestibility coefficients were calculated. Participants completed daily compliance logs and gastrointestinal symptom and bowel habit questionnaires. Fecal microbiota sequence data (V4 region, 16S rDNA gene) were analyzed using DADA2 and QIIME2.

Results: 17/19 participants completed the study per protocol. Fecal output was 40% (as-is basis) and 66% (dry matter basis) greater in the fiber condition compared to the control. Urinary energy excretion did not differ between conditions; however, fecal energy excretion was greater in the fiber condition than control (221.8 vs. 143.0 kcal/d; P< 0.01). The apparent total tract digestibility of fat was lower in the fiber condition compared to the control (92.6 vs. 93.5%, p=0.04). Microbiota analyses are ongoing.

Conclusions: Dietary fiber intake affects macronutrient digestibility.

Funding Sources: The Bell Institute of Health and Nutrition, General Mills Inc.