Dairy consumption is inversely associated with body weight. The reason for this is not known, but clinical trials and animal experiments show that consumption of high intakes of dairy causes significantly weight loss effects. One possibility is that the calcium in dairy is able to bind to fat in the gut, and this may lower the availability of fatty acids for absorption. Another possibility is that calcium regulates appetite downwards through its stimulation of calcitonin. Dairy may therefore lower energy intake through multiple mechanisms. Alternatively the conjugated linoleic acid in daily may improve insulin sensitivity and thus reduce body fat. However, recently, researchers have uncovered an association between trans-palmitoleic acid (t-POA, C16:1 (n-7)), a fatty acid present in dairy, and a reduced risk of metabolic syndrome. Because metabolic syndrome includes a cluster of metabolic abnormalities such as abdominal obesity, insulin resistance and weight gain, this association may explain the weight loss effects of dairy.
Because metabolic syndrome is a risk factor for type 2 diabetes, trans-palmitoleic acid might be associated with reduced risk of diabetes. In fact a recent paper published in the American Journal of Clinical Nutrition1 supports this contention. In the study, researchers analysed data from the Multi-Ethnic Study of Atherosclerosis that included 2617 adults, in order to compare the plasma phospholipid fatty acid profiles to a number of metabolic risk factors. In particular the researchers were interested in trans-palmitoleic acid. The results showed that trans-palmitoleic acid correlated positively with the self-reported intakes of whole fat dairy including butter. The total intake of trans-palmitoleic acid was less that 1 % of total fatty acids. In addition the trans-palmitoleic acid concentrations were associated with a lower fasting insulin level, lower systolic blood pressure and was independently associated with a lower risk of type 2 diabetes. The reduction in the incidence of type 2 diabetes was 2-fold lower in the highest compared to the lowest quartile for trans-palmitoleic acid.
These results are therefore consistent with the benefits of dairy consumption. The mechanism by which trans-palmitoleic acid might be beneficial at causing a reduction in metabolic risk factors for type 2 diabetes is not fully understood. However, it may relate to the ability of trans-palmitoleic acid to improve insulin resistance by inhibiting hepatic de novo lipogenesis. Palmitoleic acid (POA, C16:1 (n-7)) is a product of de novo lipogenesis, the formation of fatty acids from carbohydrate. This endogenously derived palmitoleic acid is in the cis form, rather than the trans form derived from dairy. When it enters circulation is does so in the very low density lipoprotein (VLDL) also called plasma triglycerides. When dairy is consumed, trans-palmitoleic acid levels rise, and this may cause counter-regulatory feedback to inhibit de novo lipogenesis and reduce cis-palmitoleic acid production. Because cis-palmitoleic acid derived from adipose tissue is thought to be a cause on insulin resistance, its inhibition may improve insulin sensitivity.
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1Mozaffarian, D., Otto, M. C. O., Lemaitre, R. N., Fretts, A. M., Hotamisligil, G., Tsai, M. Y., Siscovick, D. S. and Nettleton, J. A. 2013. trans-palmitoleic acid, other dairy fat biomarkers, and incident diabetes: the Multi-Ethnic Study of Atherosclerosis (MESA). American Journal of Clinical Nutrition. 97: 854-861
