Fatty Acids from Different Fat Sources and Dietary Calcium Concentration Differentially Affect Fecal Soap Formation...

Calcium (Ca) can complex with free fatty acids in the gastrointestinal tract (GIT), leading to the formation of insoluble unabsorbable Ca-fatty acid soaps, contributing to the proposed effect of Ca on weight loss in humans.

We determined the effect of dietary Ca concentration and the individual long-chain fatty acids on Ca-fatty acid soap formation and fatty acid digestibility.

Nine-week-old crossbreed male pigs (n = 144; mean ± SD body weight: 21.7 ± 0.15 kg) were used as an animal model for digestion in the adult human. The animals received purified diets containing 4 Ca concentrations (0, 2, 4, and 6 g/kg diet) and 4 fat sources (tallow, palmolein oil, soybean oil, and olive oil) in a completely randomized design. Fatty acids, Ca, and Ca-fatty acid soaps were determined in feces (n = 9 per diet).

Increasing dietary Ca led to a 4-fold increase (P ≤ 0.05) in excreted palmitic and stearic acid when diets contained tallow or palmolein oil as the major fat source. More than 80% of these excreted fatty acids were present as soaps. For the tallow-based diets, increasing dietary Ca led to a decrease in stearic acid digestibility from 91% to 66% (P ≤ 0.01) and in palmitic acid digestibility from 96% to 83% (P ≤ 0.01). For the olive oil- and soybean oil-based diets dietary Ca did not (P > 0.05) influence fatty acid excretion.

Ca-fatty acid soap formation led to decreased fat absorption in the GIT of growing pigs, which supports the hypothesis that higher dietary Ca concentrations reduce fat absorption.