The Higher Calcium Absorption Associated with a High Fat Diet is Not Due to Intestinal Calcium Availability

Dietary fat intake is associated with increased intestinal calcium absorption. Fatty acids (FAs) seem to influence the small intestine differently. Compared to monounsaturated FAs (MUFA), saturated FAs (SFA) decrease lipid fluidity in the membrane and bind to calcium, increasing fecal fat excretion and hence, reducing calcium bioavailability. Method: The TNO gastrointestinal model (TIM-1) replicates the biological events occurring in the lumen of the stomach, duodenum, jejunum, and ileum and was used to study the effects on food preceding absorption (i.e., bioaccessibility). A low fat and two high fat formulas (SFA or MUFA enriched) controlled for calcium (500 mg) and other micronutrients were tested in a 7-hour experiment in triplicate. Results: Calcium bioaccessibility was greater in the distal jejunum than proximal ileum (p<0.05) with the high fat diets. However, the amount of calcium absorbed through the intestinal membranes (54±1% or 275 mg) did not differ between diets. A small portion (8±0.60% or 40mg) was available for entry into the colon. A total of 37% (185 mg) was not available for absorption. Extrapolating to humans, with 1000 mg calcium intake, 630 mg would be available for absorption. Typical Ca absorption is 25% in our clinical trials, indicating that ~40% of the available Ca is absorbed (250 mg/630 mg). Conclusion These findings suggest that the up-regulation of intestinal calcium absorption with high fat intake is not due to greater available Ca from food and therefore, must have a biological basis. In vivo studies examining this relationship are ongoing in our lab. Support: Rutgers Institute Food, Nutrition, and Health.