Stearic Acid Absorption and Its Metabolizable Energy Value Are Minimally Lower than Those of Other Fatty Acids in Healthy Men Fed Mixed Diets

Abstract

Compared with other saturated fatty acids, stearic acid appears to have different metabolic effects with respect to its impact on risk for cardiovascular disease. These differences may in part reflect biologically important differences in absorption. This study was designed to compare the absorption and the metabolizable energy value of stearic acid with other fatty acids from mixed diets fed to healthy humans. Healthy men (n = 11) were fed four diets with multiple fat sources that contained ∼15% of energy (en%) from protein, 46 en% from carbohydrate and 39 en% from fat with 8 en% substitution across diets of the following: trans monoenes, oleic acid, saturated fatty acids (lauric + myristic + palmitic) or stearic acid fed as triacylglycerides. Fats were incorporated into mixed diets comprised of foods typically consumed in the United States. After a 14-d adaptation period, volunteers collected all feces for 7 d. Across diets, absorption of stearic acid (94.1 ± 0.2%) was lower (P < 0.0002) than that of palmitic acid (97.3 ± 0.2%) and higher than generally reported. Absorption of lauric, myristic, oleic, linoleic and trans 18:1 monoenes did not differ from each other (>99%) but was higher than that of stearic and palmitic acids (P < 0.001). Metabolizable energy values were similar for all fatty acids. Although absorption of palmitic and stearic acids was affected by diet treatment, the magnitudes of the differences were small and do not appear to be biologically important, at least in terms of lipoprotein metabolism. On the basis of these results, reduced stearic acid absorption does not appear to be responsible for the differences in plasma lipoprotein responses to stearic acid relative to other saturated or unsaturated fatty acids.