Dairy product consumption is associated with a lower body weight. Animal studies as well as human observational studies and human clinical trials attest to the weight loss effects of dairy products. The reason for the ability of dairy foods to improve body composition has been suggested to be due to the calcium content of the milk. The ability of calcium to bind to fat in the gut and form insoluble soaps that are not absorbed, as well as a possible role for calcium induced calcitonin release in appetite regulation, have both been hypothesised to play a role in the ability of dairy to cause weight loss. However, increasingly it appears that the fatty acids contained within ruminant milk may be the reason for the weight loss effects of dairy foods, and mounting evidence suggests that the unique fatty acid profile in dairy products may have insulin sensitising effects. For example, it is known that the conjugated linoleic acid (CLA) within ruminant products can improve insulin sensitivity in humans and animals, inducing weight loss.
Further to the hypothesis that it is the fatty acids that are the beneficial weight loss component of dairy foods, researchers have assessed the fatty acids and phospholipid species from milk and determined their relationship to insulin sensitivity1. For example, a study was performed on 86 overweight and obese subjects with metabolic syndrome, and involved measuring four variables for insulin sensitivity, the plasma fatty acid profiles of the subjects as well as their consumption of dairy products. The results of the study showed that the phospholipid lysophosphatidylcholine was positively associated with the intake of full fat dairy products consumed by the subjects. Lysophosphatidylcholine was characterised by containing two particular fatty acids (C15:0 and C17:0) which are known to be minor dietary constituents originating from ruminant products. In addition, the fatty acids C15:0, trans palmitoleic acid (trans-16:1 (n-7)), vaccenic acid (C18:1 (n-7) ) and C17:0 were all associated with full fat dairy product consumption.
Plasma levels of lysophosphatidylcholine and lyso-platelet-activating factor (PAF) were inversely associated with insulin resistance in the subjects. There was also a trend for the fatty acid C17:0 to be inversely associated with insulin resistance, but this did not reach high levels of significance. Therefore the levels of insulin resistance seen in these overweight subjects were lower at concentrations of specific phospholipids and fatty acids that are present in dairy foods. Both lysophosphatidylcholine and lyso-platelet-activating factor are membrane lipids from which one fatty acid has been cleaved leaving one acyl chain. Such phospholipids are present in only very small concentrations in milk but are present in high concentrations in milk fat globules following the activity of phospholipases. Irrespective of the origin, lysophosphatidylcholine has been shown to increase glucose clearance through stimulation of GLUT4 in adipocyte cell models, and also to lower blood glucose in diabetic and normal mice.
Dr Robert Barrington’s Nutritional Recommendation: Evidence continues to mount that dairy products are weight loss foods. These exact reason for this is not clear but many possibilities have been tested and found to have scientific validity. The ability of particular fatty acids within dairy products to cause insulin sensitising effects is compelling and a number of possible candidates have been identified. The fact that the fat might be necessary for the beneficial weight loss effects of dairy suggests that low fat dairy is a poor choice compared to its full fat alternative. The association of lyso-platelet-activating factor and insulin sensitivity is interesting because lyso-platelet-activating factor is known to oppose the inflammatory and thrombotic activity of platelet-activating-factor (PAF). The prospect that these anti-inflammatory effects may be responsible for the insulin sensitising effects of dairy is tantalising, but as yet unproven.
RdB
