The metabolic importance of unabsorbed dietary lipids in the colon

Digestion and absorption of lipids is a highly efficient process. From Western diets about 95% will be absorbed. This implies that together with lipids from endogenous sources 6-8 g of lipids will enter the colon daily. This input significantly increases during various lipid malabsorption syndromes. It has long been assumed that the biological fate of unabsorbed lipids is physiologically not relevant. However, significant microbial lipid metabolism occurs. Circumstantial evidence is arising which supports a role of unabsorbed lipid metabolites in the development of colonic diseases. Lipid metabolites may act as detergents in the colon, leading to mucosal injury and reactive hyperproliferation, which in its turn could promote tumour development. Lipid metabolites could also be transformed in biological active metabolites, which have a tumour promoting potency. More mechanistic information is needed on the colonic metabolic fate of lipids in order to develop strategies for manipulating colonic flora in the prevention of lipid related colonic diseases

The C-13-mixed triglyceride breath test in healthy adults:Determinants of the (13)CO2 response

Defects in lipolysis due to pancreatic insufficiency can be diagnosed by the mixed triglyceride (MTG) (CO2)-C-13 breath test. However, the effects of various test conditions on the (CO2)-C-13 response have only been partially elucidated. In healthy adults, we performed the (CO2)-C-13 mixed triglyceride breath test and we compared (a) the inter- and intra-individual variation in the (CO2)-C-13 response; (b) the effect of two different test meals; (c) the effect of an additional meal during the test; and (d) the effect of physical exercise during the test. Upon repeating the test in the same individual (test meal cream), repeatability coefficients were large, with respect to either time to maximum C-13 excretion rate (3.8 h), maximum C-13 excretion rate (4.9% C-13 dose h(-1)) or cumulative recovery of C-13 over the 9-h study period (22.7% C-13 dose). The cumulative C-13 expiration over 9 h obtained with the test meal composed of cream was quantitatively similar to that obtained with bread and butter: 42.2 +/- 8.4% and 47.7 +/- 6.3% respectively. Fasting for 9 h during the test resulted in similar C-13 expiration rates and cumulative C-13 expiration (43.4% +/- 7.2%) when compared with consumption of an additional meal 3 h after the start of the test (38.3 +/- 5.3%). The (CO2)-C-13 response increased in five out of seven subjects, but decreased in the other two, when moderate exercise was performed (bicycle ergometer, 50 W for 5 h). We conclude that the repeatability of the MTG test in healthy adults is low. The present results indicate that a solid and a liquid test meal, containing a similar amount of fats, give similar cumulative (CO2)-C-13 responses, and that stringent prolonged fasting during the test is unnecessary. Standardization of physical activity seems preferable, since the unequivocal effects of moderate exercise on the (CO2)-C-13 response were observed in the individuals studied

Detection of impaired intestinal absorption of long-chain fatty acids:validation studies of a novel test in a rat model of fat malabsorption

Background: Classic fat balance studies detect fat malabsorption but do not discriminate between the potential causes of malabsorption, such as impaired intestinal lipolysis or reduced uptake of fatty acids. Objective: We aimed to validate a novel test for the specific, sensitive detection of impaired intestinal uptake of long-chain unesterified fatty acids in an appropriate rat model of fat malabsorption. Design: The absorption and appearance in plasma of [C-13]palmitic acid were determined in control rats and in rats with fat malabsorption due either to chronic bile deficiency (permanent bile diversion) or to oral administration of the lipase inhibitor orlistat (200 mg/kg diet). [C-13]Palmitic acid results were compared with the percentage absorption of ingested dietary fat determined by fat balance. Results: Between 1 and 6 h after intraduodenal administration, plasma [C-13]palmitate concentrations in control rats were 4-10-fold higher than in bile-deficient rats (P <0.05) but were not significantly different between orlistat-supplemented rats and their controls. In control and bile-deficient rats, plasma [C-13]palmitate concentrations allowed complete discrimination between normal (>92%) and reduced ( Conclusions: The [C-13]palmitic acid absorption test detects impaired intestinal absorption of long-chain fatty acids selectively and sensitively in a rat model of fat malabsorption due to bile deficiency. Our data strongly support the use of the [C-13]palmitic acid absorption test for the diagnosis of clinical fat malabsorption syndromes