A body of literature suggests that elevated dietary calcium intake can lead to reduced body weight. However, the mechanisms whereby this may occur have yet to be fully described. One hypothesis is that calcium promotes the formation of calcium soaps when it binds to fatty acids in the small intestine, rendering the fatty acids unavailable. To test this hypothesis, Stroebinger and colleagues conducted a study using multiple levels of calcium and sources of fats and report their results in the May 2021 issue of The Journal of Nutrition.
The experiment used male pigs provided purified diets containing four calcium concentrations (0, 2, 4, or 6 g/kg diet) along with four sources of fat (tallow, palmolein oil, soybean oil, or olive oil) in a completely randomized block design. The diet was provided in three equal meals for 9 days, with samples of feces collected on days 7-9. Analyses included fatty acids, calcium and calcium fatty acid soaps (n=9/diet).
Excretion of palmitic acid and stearic acid was increased by increased calcium intake when the diets contained either tallow or palmolein oil, and more than 80% of the excreted fatty acids were present as calcium soaps. Significant reductions in stearic acid and palmitic acid digestibility occurred with increased calcium content in the tallow-based diets. There was no change in fatty acid excretion when calcium levels were increased in diets containing olive oil or soybean oil. These observations led the authors to conclude that calcium fatty acid soaps reduce fat absorption.
In a commentary on this article, Zijlstra discusses the potential mechanisms contributing to reduced body weight when calcium is added to diets containing different fat sources. Zijlstra notes the elevated calcium soaps formed were associated with saturated fatty acids in the diet sources, particularly when the saturated fatty acids made up 40% of the fat source used. Zijlstra concludes that more work is needed in order to identify where the soaps are being formed and under what conditions their formation is promoted.
References
Stroebinger N, Rutherfurd SM, Henare SJ, Hernandez JFP, Moughan PJ. Fatty acids from different fat sources and dietary calcium concentration differentially affect fecal soap formation in growing pigs. Journal of Nutrition, Volume 151, Issue 5, May 2021, Pages 1102–1110, https://doi.org/10.1093/jn/nxaa438.
Zijlstra RT. Binding fatty acids into indigestible calcium soap: Removing a piece of pie Journal of Nutrition, Volume 151, Issue 5, May 2021, Pages 1053–1054, https://doi.org/10.1093/jn/nxab045.
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