Effect of dairy calcium on fecal fat excretion: a randomized crossover trial

Background: Evidence suggests that dietary calcium intake may be inversely related to body weight. One explanatory mechanism is that dietary calcium increases fecal fat excretion, due to either calcium soap formation and/or binding of bile acids (BAs) in the intestine. Objective: To examine the effect of calcium from low-fat dairy products on fecal fat excretion. Design: A randomized crossover study with 11 subjects, comparing two 7-d diets: one high in calcium from low-fat dairy products (high-Ca; 2300 mg Ca per d) and one low in calcium (low-Ca; 700mg Ca per d). Measurements: All feces were collected during the last 5 days of each diet period and analyzed for fat, energy and calcium content and fatty acid (FA) and BA composition. Results: Dairy calcium significantly increased the total fecal fat excretion from 5.4 +/- 0.5 g d(-1) on the low- Ca diet to 11.5 +/- 1.4 g d(-1) on the high-Ca diet (P < 0.001). The fecal energy excretion increased almost correspondingly. Saturated, monounsaturated and polyunsaturated FAs were all excreted in larger amounts on the high-Ca diet (P < 0.001 for all), with the effect of calcium being greater for monounsaturated than for saturated FAs. The fecal excretion of BAs was unaffected of calcium intakes. Conclusions: Increasing the intake of calcium from low- fat dairy products by 1600 mg d(-1) for 7 days doubled total fecal fat excretion, but did not affect the excretion of BAs. The results may partially explain why a high-calcium diet can produce weight loss.