(AL05-01-25) 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: Our primary objective was to evaluate dietary metabolizable energy with and without high-fiber cereal. Secondary objectives included evaluating the effects of the high-fiber cereal on the gut microbiota. We hypothesized that including a high-fiber cereal would reduce the metabolizable energy of the diet.

Methods: Healthy adults (n=19) participated in a double-blind, randomized, controlled, crossover study with two experimental conditions (2 wks 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, scaled such that participants remained weight stable; the base diet was supplemented with either 3 servings/d (282 total kcal) of a low (1 g) or high (30 g) fiber cereal. After a 9-d acclimation period, participants collected all urine and fecal samples produced over 5 d. 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. Amplicon (V4) sequencing was conducted to characterize the fecal microbiota. Fecal microbial cells (qPCR) and protein (BCA assay) were quantified. Fecal bile acids were measured using LC-MS/MS. Participants completed daily compliance logs and GI symptom and bowel habit questionnaires.

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. 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). In the fiber condition, fecal microbial protein (p=0.01) and microbial cells were greater (p=0.07). GI tolerance symptoms did not differ between conditions.

Conclusions: Consuming a high-fiber cereal impeded fat digestibility and increased total fecal energy excretion. Fecal output, microbial cells, and microbial protein were greater in the fiber condition. The high-fiber cereal was well tolerated by participants.

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