It is well reported that both dairy products and calcium intakes are inversely related to body weight. In addition, animal experiments show that administration of dairy and calcium to experimental animals causes changes in physiology that result in weight loss. Clinical randomised trials involving human subject have also yielded positive results that attest to the fat loss effects of dairy and calcium. It is unclear if the fat loss effects of dairy products are due solely to the calcium they contain, or if some other factor also plays a role. For example, conjugated linoleic acid is also present in dairy foods and this may contribute to the observed fat loss effects of full fat dairy products. Also it is unclear as to the mechanisms by which calcium or dairy product could cause fat loss, although an improvement in insulin sensitivity and a decrease in appetite have been suggested as possible mechanisms of action. Dairy food may be particularly effective at decreasing abdominal or truncal fat.
Researchers have compared high and low calcium diets for their effects on fat loss. For example, in one study1, researchers randomly assigned overweight and obese subjects to receive an energy reduced diet providing a deficit of 500 kcals which contained 500 mg per day calcium, or a similar diet that contained yoghurt and which provided 1200 mg per day calcium. The subjects consumed this diet for 12 weeks and during this time a detailed analysis of their body composition was obtained. Weight loss was significantly greater in the yoghurt diet (-6.63 kg) compared to the control diet (-4.99 kg). Fat loss was significantly higher in the yoghurt diet (-4.43 kg) compared to the control diet (-2.76 kg). The fat loss in the yoghurt group was typified by a higher loss of truncal and visceral fat and this was reflected in a greater reduction in waist circumference in the yoghurt compared to the control diet. The loss of lean mass was greatest in the control diet, suggesting that the yoghurt diet has muscle sparing effects.
Taken as a whole these results suggest that yoghurt has beneficial fat loss effects. However, it is unclear if this is due to the calcium content or some other factor. High calcium diets may improve insulin sensitivity through reversal of depleted calcium levels. However, yoghurt may have other beneficial effects. For example, yoghurt can modify and improve the bacterial content of the colon through the supply of prebiotics and changes to the pH of the gut, and this may have beneficial effects on inflammation, which in turn could improve oxidative stress and insulin sensitivity. Full fat dairy foods also contain other substances such as conjugated linoleic acid which has been shown to improve insulin sensitivity. Lastly, yoghurt may decrease appetite because of the way it affects the chemistry of the gastrointestinal tract. The fact that central adiposity was noticeably improved in the subjects however suggests that the mechanism of action of yoghurt involved a reversal of insulin resistance.
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