Calcium as Part of a Normal Protein Diet May Increase Fecal Fat and Energy Excretion

Laurie Barclay, MD

March 29, 2005

March 29, 2005 — Calcium, taken along with a normal protein diet, increases fecal fat and energy excretion, according to the results of a randomized crossover study published in the April issue of the International Journal of Obesity. The investigators suggest that this may help explain weight loss from high-calcium diets.

"Observational studies have shown an inverse association between dietary calcium intake and body weight, and a causal relation is likely," write R. Jacobsen, MD, from the Royal Veterinary and Agricultural University in Frederiksberg, Denmark, and colleagues. "However, the underlying mechanisms are not understood."

Ten subjects each received three isocaloric one-week diets containing low calcium and normal protein (LC/NP; 500 mg calcium; 15% of energy from protein), high calcium and normal protein (HC/NP; 1,800 mg of calcium; 15% of energy from protein), and high calcium and high protein (HC/HP; 1,800 mg of calcium; 23% of energy from protein).

Although calcium intake did not affect 24-hour energy expenditure or fat oxidation, fecal fat excretion increased approximately 2.5-fold during the HC/NP diet compared with the LC/NP and the HC/HP diets (14.2 vs 6.0 and 5.9 g/day; P < .05). The HC/NP diet also increased fecal energy excretion compared with the LC/NP and the HC/HP diets (1,045 vs 684 and 668 kJ/day; P < .05). Calcium intake did not affect levels of blood cholesterol, free fatty acids, triacylglycerol, insulin, leptin, or thyroid hormones.

Study limitations include not testing the effect of calcium on appetite and energy intake, so it is possible that calcium may also have metabolic effects resulting in suppression of energy intake. Effects on energy metabolism also could not be excluded due to the short duration of the study.

"A short-term increase in dietary calcium intake, together with a normal protein intake, increased fecal fat and energy excretion by [approximately] 350 kJ/day," the authors write. This observation may contribute to explain why a high-calcium diet produces weight loss, and it suggests that an interaction with dietary protein level may be important."

The Danish Dairy Board and the Danish Ministry of Food, Agriculture, and Fisheries supported this study.

Int J Obesity. 2005;29:292-301

Reviewed by Gary D. Vogin, MD

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