Marked resistance of normal subjects to tube-feeding-induced diarrhea: the role of magnesium

The tolerance of healthy subjects to increasing rates of tube feeding was studied to better understand the etiology of diarrhea among tube-fed patients. Five volunteers were fed Osmolite HN by continuous duodenal infusion beginning at 314 kJ (75 kcal)·kg body wt−1 · d−1 and progressing each 24 h until no longer tolerated. The five subjects were able to tolerate maximum 24-h infusions of 331–511 kJ·kg−1 · d−1 (198–340 mL/h). Diarrhea developed in only three subjects. Compared with nondiarrheal stools, the high-speed supernatant of the diarrheal stools had significantly higher concentrations of magnesium (192 ± 22 mmol/L vs 139 ± 17 mmol/L, P = 0.005), lower concentrations of potassium and phosphorus, and similar concentrations of calcium. The mean carbohydrate, fat, and nitrogen contents were not significantly different. We conclude that normal adult males are remarkably tolerant to duodenal infusion of this typical, isotonic tube-feeding product. The diarrhea that occurred in three of the volunteers at very high infusion rates appeared to be osmotic and attributable predominantly to magnesium.