The paper by Thompson et al. in this issue shows that adding increased dietary calcium (from 800 mg/d to 1, 400 mg/d) to a hypocaloric diet via two additional servings of dairy has no effect on weight or fat loss after a 48 week study in 90 obese men and women. This result confirms similar findings by Bowen et al. (1) and Shapses et al. (2). The former compared a hypocaloric diet with 500 mg of calcium/d with one containing 2, 400 mg/d (predominantly from dairy) in 50 subjects; the latter, a study that focused on bone changes with weight loss, added 1, 000 mg/d of elemental calcium to a hypocaloric diet.
Recent epidemiological data have shown that, over 3 years, a weight increase in 12, 000 children was directly related to the number of servings per day of dairy calcium or dairy protein (3). The suggested mechanism of dietary calcium-induced fatty acid release from adipocytes and enhanced fatty acid oxidation and energy expenditure has not been confirmed in either rats (4) or humans (5).
The animal study data (4) show that increased dietary calcium led to greater fat loss in the feces, which could account for the observed difference in weight. In the human studies (5), the low calcium diet contained 500 mg of calcium/d, which is the level Zemel suggests is required before the addition of extra calcium can have an effect on energy balance.
Moreover, findings in lean or obese rats with low calcium diets and calcium supplementation (6) have not been confirmed (7, 8). The Zemel group (9) has shown that intracellular calcium can be elevated by depolarization with KC1, which then inhibits lipolysis. Adrenergic stimulation (particularly alpha-1) also elevates intracellular calcium (10) but enhances lipolysis (11). The intracellular calcium story is, thus, not completely clear, especially with physiological stimuli.
In conclusion, increased dietary calcium may have a small effect on energy balance via fecal loss of lipids, but there appears to be no effect of calcium to enhance lipid oxidation. Very large long-term trials would be required to show a significant effect on weight. There is no clear evidence that dairy-derived calcium would be any more effective in causing fecal energy loss than non-dairy calcium.