While some calorie-conscious people may drop dairy products when they're dieting, a new study suggests this strategy could backfire. The study to be published in the upcoming April issue of the International Journal of Obesity reveals that yogurt may help turn up the body's fat-burning ability - making it easier to lose fat while maintaining lean muscle.

"We have previously demonstrated an antiobesity effect of dietary Ca; this is largely mediated by Ca suppression of calcitriol levels, resulting in reduced adipocyte intracellular Ca2+ and, consequently, a coordinated increase in lipid utilization and decrease in lipogenesis," write M. B. Zemel, from the University of Tennessee in Knoxville, and colleagues. "Notably, dairy Ca is markedly more effective than other Ca sources."

In this study, 34 obese subjects were placed on a balanced deficit (–500 kcal/day) diet and randomized to control (400-500 mg Ca/day; n = 16) or yogurt (1,100 mg Ca/day; n = 18) treatments for 12 weeks. Macronutrients and fiber in the diets of both groups were held constant at the U.S. average. At baseline and after 12 weeks, the investigators measured body weight, body fat and fat distribution, blood pressure, and circulating lipids.

For patients on the yogurt diet, fat loss was dramatically increased (–4.437 ± 0.47 vs –2.757 ± 0.73 kg in the control group; P < .005), and lean tissue loss was reduced by 31%. Truncal fat loss was increased by 81% for patients on the yogurt diet compared with those on the control diet (P < .001), as reflected in a much greater reduction in waist circumference (–3.997 ± 0.48 cm vs –0.587 ± 1.04 cm; P < .001). Compared with the control group, the proportion of fat lost from the trunk was higher in the yogurt diet group (P < .005).

"Isocaloric substitution of yogurt for other foods significantly augments fat loss and reduces central adiposity during energy restriction," the authors write. "These data add to a growing body of observational and clinical observations that support a role for dietary calcium and dairy foods in controlling excess adiposity."

They cite other clinical trials showing that dairy has a greater effect on adiposity than does an equivalent amount of calcium from supplemental or fortified sources.

"Although the mechanism for this additional effect is not clear, we have previously proposed that it may be attributable, in part, to additional dairy bioactive compounds, such as angiotensin converting enzyme inhibitors, which may act on the adipocyte renin–angiotensin system, as well as to the high concentration of branched-chain amino acids in dairy," the authors note. "Recent studies demonstrating a potential role for autocrine production of cortisol by adipose tissue in the generation of truncal obesity have prompted us to explore whether the increase in calcitriol, which occurs in response to low-calcium diets, might play a regulatory role in adipocyte cortisol production.

In an accompanying editorial, R.B.S. Harris, from the University of Georgia in Athens, calls these results "impressive."
"At a time when obesity in both adults and children has reached alarming levels in the United States, it is important to identify any dietary change that is useful in preventing or ameliorating weight gain," Dr. Harris writes. "Therefore, the concept of a beneficial effect of calcium and of low-fat dairy products on body weight is very attractive: not only would there be a benefit in terms of body weight but there also is the potential of increasing consumption of high-quality protein and of calcium in an adult population that has a daily calcium intake below the [recommended daily allowance].

"For many in the scientific community, however, it is difficult to embrace the efficacy of dietary calcium and dairy protein without a good understanding of the mechanisms responsible for the loss of body fat," according to Dr. Harris.

Source: Diabetes In Control.com: Int J Obes. 2005;29:388-390, 391-397Dairy (yogurt) augmentation of total and central fat loss in obese subjects. Zemel MB, Richards JD, Mathis S, Milstead AM, Gebhardt LP, Silva E. The University of Tennessee, Knoxville, TN 37996-1920.