Intestinal Energy Absorption Is Associated with Glycemic Variability in Young, Healthy Adults

Although it is well established that humans are not capable of absorbing 100% of gross energy consumed from the diet, little is known regarding the association between intestinal energy absorption (i.e., digestibility) and metabolic health and gastrointestinal function.

The objective of this secondary analysis was to determine associations between energy digestibility and markers of cardiometabolic health and gastrointestinal function.

Sixteen healthy adults consumed a weight-maintenance controlled diet for 9 d. During days 4-7, participants collected all stool and urine, which allowed for the measurement of energy and macronutrient loss and determination of digestibility (i.e., energy absorption). Relationships between energy digestibility, gastrointestinal transit time, and cardiometabolic health outcomes were assessed by Pearson and Spearman correlations. Multivariable regression analysis was used to identify variables that could be collected in the laboratory and serve as a surrogate measure of energy digestibility.

Mean energy digestibility was 91.7% ± 1.5% with individual digestibility values ranging from 89.7% to 94.3%. Wet (r = -0.89, P < 0.0001) and dry stool weight (r = -0.89, P < 0.0001), gross energy intake (r = -0.53, P = 0.034), and fiber intake (r = -0.53, P = 0.034) were inversely associated with digestibility. Glucose variability (mean amplitude of glycemic excursions; r = 0.68, P = 0.0056), colonic transit time (r = 0.63, P = 0.016), age (r = 0.63, P = 0.0093), and whole-gut transit time ( r = 0.54, P = 0.032) were positively associated with digestibility. Furthermore, in a multiple linear regression model, 95% of the variability in energy digestibility was explained by the dry weight of stool (g/d), 24-h blood glucose variability (mean amplitude of glycemic excursions; mg/dL), colonic transit time (h), whole-gut transit time (h), and age (y; adjusted R² = 0.95, P < 0.0001).

Energy digestibility is an important physiological variable associated with gastrointestinal function and glucose variability and should be considered in future precision nutrition trials.

This study was registered at the Florida State University Institutional Review Board and registered on clinicaltrials.gov as registration number NCT04877262 (https://clinicaltrials.gov/study/NCT04877262?id=NCT04877262&rank=1).