In the intestine the fatty acids at the sn-1 and sn-3 positions are released from the structural backbone through the action of digestive enzymes. These released free fatty acids and the glycerol backbone with a fatty acid attached at sn-2 can then be absorbed by the intestinal wall.
In human breast milk, palmitic acid is mainly attached at the central sn-2 position of the structural backbone, whereas the sn-1 and sn-3 postions are mainly occupied by unsaturated fatty acids are easily absorbed by the intestinal wall and enter the bloodstream. The same is true for the palmitic acid which remains attached to the structural backbone.
In cow's milk and in unmodified vegetable oils - present in standard infant formula - palmitic acid is mainly attached at the external sn-1 and sn-3 positions. The palmitic acid which is released from the backbone by the digestive enzymes tends to react with calcium present in the intestinal lumen. This results in the formation of insoluble calcium soaps, from which the palmitic acid and calcium cannot be absorbed. As a consequence the energy (palmitic acid) and calcium supply to the infant is less efficient.
Two problems can arise if dietary saturated fatty acids such as palmitic acid are not extensively absorbed. Firstly, the amount of vital energy available to the growing infant is substantially reduced, and this may have detrimental effects on the baby's ability to thrive. Secondly, and equally important, free saturated fatty acids have a tendency to clump together with dietary calcium, making it impossible for calcium to enter the bloodstream and be used in the normal development of healthy bones. Excessive loss of calcium through the intenstine also hardens the stools and can lead to uncomportable constipation and distressing colic. Clearly the distribution of the fatty acids on the backbone has an important role in energy and mineral absorption.