Context:In various observational studies, an inverse relation between calcium intake and body weight has been observed. A possible explanation could be an increased calcium excretion through the faeces caused by an increased dietary calcium intake.Objective:To examine whether an increased calcium intake could lead to changes in faecal fat and energy excretion.Design:Four different isocaloric diets with various calcium contents (400, 1200 and 2500 mg from dairy and 1200 mg from calcium carbonate (1200S)) were administered in a crossover design for 7 days each.Subjects:Five healthy men and five healthy women (age=28+/-2, body mass index=24.1+/-0.4, body fat%=25.6+/-2.4) were recruited by local announcement.Measurements:At the end of every intervention period, faecal samples were collected for determination of fat, energy and calcium content, blood samples were obtained for determination of relevant blood parameters; and fat samples were obtained for measurement of the mRNA expression. Furthermore, resting energy expenditure and fat oxidation were measured with the ventilated-hood technique.Results:We observed a non-significant 56% increase in fat excretion (P=0.159) on the 2500 mg diet, compared to the 400 mg diet. The 2500 mg diet significantly reduced the expression of fatty acid synthase (FAS) mRNA (P<0.05) and the calcium content of the diets significantly affected calcium excretion. Furthermore, we saw a significant decrease of serum triglycerides on the 1200S diet (P<0.05).Conclusion:In this study, we observed a trend towards a higher fat excretion on the high-calcium diet, but this difference failed to reach statistical significance. It is possible that the relatively high protein content of the experimental diets increased calcium absorption from the intestine, thus decreasing the amount of calcium available for binding to fat and eliminating possible effects of dietary calcium on fat excretion. Furthermore, we observed decreases in FAS mRNA expression and serum triglycerides as a result of a high calcium intake.International Journal of Obesity advance online publication, 19 June 2007; doi:10.1038/sj.ijo.0803660.