Dairy consumption is associated with weight loss. This may relate to the calcium content of dairy as high calcium diets reduce the risk of obesity. Mechanistically the effects of calcium on weight loss have been investigated and a number of mechanisms have been proposed and tested. One mechanisms suggested involves the ability of calcium to bind to fatty acids in the gut forming insoluble soaps. Alternatively the calcium may form insoluble conjugates between calcium phosphate complexes and bile acids. These soaps are then excreted increasing the amount of faecal fat. Another possible mechanisms involves the ability of calcium to regulate appetite. In this respect high gut calcium levels may increase the release of calcitonin from the thyroid gland in preparation for increased excretion of calcium from the kidney. As plasma calcitonin levels rise this may act as a satiety signal in the hypothalamus and thus regulate appetite downwards. Calcium therefore appears to have particular weight loss properties.
Researchers1 have compared the effects of milk and cheese based diets on the degree of fat excretion and to changes to appetite in healthy individuals. The 15 subjects consumed either a high milk (1700 mg per day calcium), high cheese (1700 mg per day calcium) or a low cheese and milk control diet (500 mg per day calcium) in a randomised cross over design trial (all groups consumed each diet for 2 weeks in a random order). The diets were isocaloric and contained similar amounts of fat. The diets were controlled so that they only differed in the amount of calcium they provided from dairy products. The results of the study showed that faecal fat excretion increased more with consumption of the milk (+5.2 grams per day) and the cheese diet (+5.7 grams per day) compared to the control diet (+3.9 grams per day), but that the milk and cheese diet showed no significant differences from one another. The cheese diet also caused a significant reduction in insulin levels compared to the control and milk diet.
There were no differences between the treatment and control groups for blood pressure, triglycerides, lipid ratios or appetite ratings. All three diets increased the low density lipoprotein (LDL) plasma levels, and the authors attributed this to the high saturated fatty acid content of the diet. However, this is an example of unsubstantiated opinion masquerading as science as it is not possible to make this claim based on the data due to a lack of adequate controls. The LDL plasma levels could have risen for any number of reasons based on differences between the normal diets of the subjects to the treatment and control diets. For example, the fibre content of the three diets was quite low and this may have caused the increase in LDL plasma levels. In fact the rise in LDL plasma levels were attenuated somewhat by the milk and cheese diets, arguing against the role of saturated fat alone in causing changes to LDL plasma levels. These results support the contention that calcium increases the excretion of dietary fat.
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