A review by Teegarden (2003) was one of the most substantial early contributions to the hypothesis regarding calcium's role in accelerating weight loss. The review brought together a broad range of trials dating back 10 years to the original findings demonstrated on hypertensive rats. In an updated review published in 2005, while acknowledging the promising data that has emerged over the intervening 2 years, Teegarden notes that the current body of evidence has a number of limitations and flaws that need to be addressed before the full extent of calcium's effect on weight loss can be determined.
Although the underlying mechanism of action remains unclear, there is general acceptance that high calcium intake depresses PTH levels and 1,25(OH)2D, which in turn decreases intracellular calcium, thereby potentially inhibiting lipogenesis and stimulating lipolysis within the cells (McCarty & Thomas 2003, Schrager 2005, Zemel et al 2004). Additional proposed actions include increased rates of faecal fat and energy excretion (14.2 g/day vs 5.9 g/day and 1045 kJ/day vs 684 kJ/day), as observed in a preliminary study of 10 subjects, during a 1 -week high-calcium and normal protein diet (1800 mg/day and 1 5% of total energy intake, respectively) (Jacobsen et al 2005). Interestingly, these increased losses were not evident when high calcium and protein intake was combined (23%).
One prolific researcher in this area is Zemel (2004, Zemel et al 2004, 2005a, b), who has published three small trials investigating the effects of dietary and supplemental calcium in patients for weight maintenance or weight loss. These trials have consistently yielded positive results, demonstrating that in addition to enhanced weight loss on isocaloric and identical macronutrient profiles, with or without energy restriction, a diet providing high calcium levels of 1100-1200 mg/day results in central fat loss and corresponding improvements in blood pressure, insulin sensitivity and retention of lean tissue. Australian researchers Bowen et al have also demonstrated similar results (2004).
Zemel et al conclude that dietary calcium and, in particular, dairy based foods are the most effective form of calcium for weight loss and that results are significant within 12 weeks.
In stark contrast to this, there have been a number of studies reporting negative results. Atrial of isocaloric energy restricted diets in 54 overweight subjects with either low or high calcium intake from dairy products found that over 12 months there was no significant difference in weight loss between the two groups (Harvey-Berino et al 2005). Other studies incorporating calcium supplements of 1000 mg/day Calcium 159
yielded negative results over 3 25-week periods in pre- and postmenopausal women
(Shapses et al 2004), as did a longitudinal study of dietary habits in adolescents (Berkey et al 2005).
Finally caution is being encouraged by many authorities who are keen to remind researchers that epidemiological data have positively linked high dairy diets with a range of other conditions, most notably prostate cancer (Lanou 2005).
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