The mechanism of lowering cholesterol absorption by calcium studied by using an in vitro digestion model

Abstract

Studies in humans show that a calcium-enriched diet leads to lower cholesterol in blood serum. This phenomenon is usually explained in the literature with a reduced cholesterol absorption in the small intestine. Our study aims to clarify the effect of calcium on the solubilisation of cholesterol and fatty acid in the dietary mixed micelles (DMM), viz. on the bioaccessibility of these lipophilic substances in the gut. We use an in vitro digestion model which mimics very closely the intestinal pH-profile and the composition of the intestinal fluids. We quantified the effects of Ca(2+) concentration on the lipid solubilization for fats and oils with different saturated/unsaturated fatty acid (FA) contents. We found that the increase of calcium significantly decreases the solubilization of cholesterol, FA and MG. Most importantly, we observe a clear positive correlation between the amounts of solubilized cholesterol, on one side, and solubilized free fatty acids and monoglycerides, on the other side. The main conclusion is that Ca(2+) ions strongly affect the bioaccessibility of both cholesterol and saturated FA. Therefore, calcium may decrease the serum cholesterol via two complementary mechanisms: (1) fatty acid precipitation by calcium ions reduces the solubilisation capacity of the DMM, thus decreasing the levels of solubilised (bioaccessible) cholesterol; (2) the observed strong decrease of the bioaccessible saturated FA, in its own turn, may suppress the cholesterol synthesis in the liver.

Epidemiology of urolithiasis in Asia

“…Precursors of oxalate in food (like glycine, hydroxyproline, hydroxyacetic acid and vitamin C) may be metabolized to oxalate in liver, and subsequently increase the oxalate concentration in urine. The combination of lipid and calcium in intestine, forming insoluble substance, can also inhibit calcium absorption, followed by increasing absorption of oxalate [70] . Hyperuricemia, the main risk factor for uric acid stones, can also be the result of excessive consumption of meat [71] .…”

Anti-Obesity Effects of Dietary Calcium: The Evidence and Possible Mechanisms

“…Moreover, short-term dietary calcium fortification (2200 mg/day total and 550 mg calcium citrate malate) significantly increased dietary saturated fat excreted from 6% to 13% in men [110]. It has been implicated that the formation of insoluble calcium soaps and the alteration of the interfacial organization of hydrolyzed lipids are involved in calcium-induced decreased fat digestion and absorption and increased fecal fat secretion [111,112]. Taken together, the beneficial roles of calcium in decreasing fat absorption and increasing fecal fat excretion might be responsible for its anti-obesity effects.…”

The soluble fraction of soy protein peptic hydrolysate reduces cholesterol micellar solubility and uptake

“…However, apart from different amino acid composition, the difference of other constituents between two samples may also affect cholesterol micellar solubility and uptake. For instance, in the process of traditional hard tofu (HHT samples), more ion of Ca 2+ was used, which strongly affect the bioaccessibility of cholesterol (Vinarova et al, 2016). On the other hand, as above mentioned, different polysaccharides content could play a certain role to this effect as well.…”