Intestinal carbohydrate absorption and permeability at high altitude (5,730 m)

To investigate the effects of high altitude on intestinal function, the absorption and permeation of nonmetabolizable carbohydrates were measured in 14 volunteers (median age 21 yr, range 19-37 yr) at sea level in Oxford, UK; at 1,050 m in Nepal; at 5,570 m after 5 days at > 5,500 m; and at 5,730 m after 11 days at > 5,500 m. Body weight decreased 5.7 +/- 1.19 kg from sea level to 5,570 m (P < 0.001 by paired t test) despite 72-h dietary records showing no change in energy intake. Absorption of carbohydrates by mediated transport was measured by urinary xylose and 3-O-methyl-D-glucose excretion. Xylose excretion (%oral dose) decreased from 31.4 +/- 4.5% to 20.7 +/- 4.5% (P < 0.001) and 3-O-methyl-D-glucose excretion decreased from 39.7 +/- 6.1 to 33.7 +/- 7.0% (P = 0.003) from sea level to 5,730 m. Monosaccharide permeation measured by L-rhamnose excretion decreased from 11.3 +/- 2.5 to 6.2 +/- 2.0% (P = 0.001). Intestinal permeability, a measure of barrier function (ratio of lactulose to L-rhamnose), increased from 0.036 +/- 0.014 at sea level to 0.084 +/- 0.042 at 1,050 m (P = 0.006), possibly due to infective enteropathy after arrival in Nepal, but reverted to normal (0.045 +/- 0.013; P = 0.062) at 5,730 m. Absorption of all carbohydrates returned to normal after return to the UK. This study showed that a decrease in mediated (D-xylose or 3-O-methyl-D-glucose) and diffusional (L-rhamnose) monosaccharide absorption occurs at high altitude but that intestinal permeability at 5,730 m is unchanged.