Bomb calorimetry, the gold standard for assessment of intestinal absorption capacity: normative values in healthy ambulant adults.

BACKGROUND: Intestinal absorption capacity is considered to be the best method for assessing overall digestive intestinal function. Earlier reference values for intestinal function in healthy Dutch adults were based on a study that was conducted in an inpatient metabolic unit setting in a relatively small series. The present study aimed to readdress and describe the intestinal absorption capacity of healthy adults, who were consuming their usual (Western European) food and beverage diet, in a standard ambulatory setting. METHODS: Twenty-three healthy subjects (aged 22-60 years) were included in the analyses. Nutritional intake (energy and macronutrients) was determined with a 4-day nutritional diary. Subsequently, mean faecal losses of energy (by bomb calorimetry), fat, protein and carbohydrate were determined following a 3-day faecal collection. Finally, intestinal absorption capacity was calculated from the differences between intake and losses. RESULTS: Mean (SD) daily faeces production was 141 (49) g (29% dry weight), containing 891 (276) kJ [10.7 (1.3) kJ g(-1) wet faeces; 22.6 (2.5) kJ g(-1) dry faeces], 5.2 (2.2) g fat, 10.0 (3.8) g protein and 29.7 (11.7) g carbohydrates. Mean (SD) intestinal absorption capacity of healthy subjects was 89.4% (3.8%) for energy, 92.5% (3.7%) for fat, 86.9% (6.4%) for protein and 87.3% (6.6%) for carbohydrates. CONCLUSIONS: The present study provides normative values for both stool nutrient composition and intestinal energy and macronutrient absorption in healthy adults on a regular Dutch diet in an ambulatory setting. Intestinal energy absorption was found to be approximately 90%.

Assessment of small bowel function in critical illness: potential role of citrulline metabolism.

Small intestinal function in critically ill patients should ideally be assessed in order to determine the preferred feeding route, timing, and composition of enteral nutrition. Additionally, evaluation of small bowel function may lead to new insights aimed to maintain enterocyte integrity. Critically ill patients are likely to have impaired enterocyte function mainly as a consequence of diminished splanchnic blood flow associated with mucosal hyperpermeability and bacterial translocation, a pathological state believed to be pivotal in the development of sepsis and multiple organ dysfunction syndrome (MODS). However, feasible and validated clinical tools to reliably assess enterocyte function are lacking. This explorative review discusses the promising role of citrulline, a nonprotein amino acid almost exclusively generated by the enterocyte, as a biomarker reflecting enterocyte function in critically ill patients. Citrulline metabolism, its potential as enterocyte biomarker, and literature on citrulline in critically illness will be discussed. Finally, a novel test for enterocyte function, the citrulline generation test (enterocytic citrulline production upon stimulation with enteral or intravenous glutamine) will be considered briefly.

The citrulline generation test: proposal for a new enterocyte function test.

BACKGROUND: The amino acid citrulline is mainly produced by enterocytes from conversion of glutamine. As fasting plasma citrulline proved disappointing as a biomarker for enterocyte dysfunction in clinical practice, we propose a citrulline generation test (CGT) to assess enterocyte function. AIM: To assess the feasibility of a CGT in healthy subjects and patients with decreased enterocyte mass. METHODS: Nineteen healthy subjects, 16 patients with intestinal villous atrophy and nine patients with short bowel syndrome (SBS) were given an oral bolus of 20 g of the dipeptide alanine-glutamine. Subsequent changes in plasma citrulline and other amino acid concentrations were determined using reverse-phase high-performance liquid chromatography. RESULTS: Following the oral bolus of alanine-glutamine, plasma citrulline concentrations showed a time dependent rise in healthy subjects of 44 +/- 13% (38-55 micromol/L, P < 0.0001). The slope from baseline plasma citrulline to peak concentrations was 0.22 +/- 0.08, 0.13 +/- 0.04 and 0.09 +/- 0.04 micromol/L/min in healthy subjects, patients with coeliac disease (CeD) and refractory CeD, respectively (healthy subjects vs. CeD P < 0.05, healthy subjects vs. refractory CeD P < 0.001). In patients with SBS, the CGT was able to distinguish between non-adapted and adapted SBS by means of the incremental area under the CGT curve till 90 min (iAUC T90). The iAUC T90 was 447 +/- 179 and 1039 +/- 178 micromol/L/min in non-adapted and adapted SBS, respectively (P = 0.04). CONCLUSION: An oral bolus of alanine-glutamine induces a time-dependent rise in plasma citrulline concentration to an extent dependent on the existence of villous atrophy or enterocyte hyperplasia in CeD, and adapted SBS, respectively.