Impaired Intestinal Function Among Indigenous Shuar Children of Amazonian Ecuador: Evidence From Lactulose:Mannitol Tests of Absorption and Permeability

Objectives: Intestinal function is an important but often overlooked aspect of human biological variation, with the intestines serving as both a barrier against external pathogens/contaminants and the primary conduit of nutrient extraction from food. Impaired intestinal function among children is viewed as a key contributor to growth faltering globally. However, few studies have investigated children's intestinal function in rural settings or beyond infancy. To address this limitation, we conducted a pilot study to describe the intestinal function of school-age Indigenous Shuar children of Amazonian Ecuador and to assess the feasibility of implementing the widely utilized lactulose:mannitol (L:M) test of absorption and permeability with this group. Methods: The urinary L:M test was performed with 23 rural-living Shuar children aged 4–12 years. Ultra-performance liquid chromatograph–high-resolution mass spectrometry was used to determine L:M ratios, lactulose recovery, and mannitol recovery. Age and sex patterns were investigated using linear regression models. Results: Children's mean L:M ratio was 0.33 ± 0.32, a ratio comparable to values reported for children in other low- and middle-income settings. 35%–91% of children were categorized as having impaired intestinal function using common cut-off values. Children's lactulose (0.14% ± 0.17%) and mannitol (2.60% ± 2.22%) recoveries did not differ by sex but increased with age (p < 0.05) and indicated diminished intestinal absorptive capacity and increased permeability. Conclusions: Intestinal function appears to be considerably impaired among school-age Shuar children living in a low-resource, rural setting. Children living in unsanitary, non-industrialized contexts may routinely experience intestinal permeability-related immune activation and malabsorption-related energy/nutrient loss. More research is needed to explore the breadth of global variation in children's intestinal function and to investigate its many evolutionary and public health implications.