Milk fats: A different perspective

The recent history of public recommendations for dietary intakes of macronutrients have targeted total fat, cholesterol and saturated fat intake as the principle means to improve human health. Such recommendations have been translated into a long term agricultural objective of eliminating these components from human foods. Agricultural change requires changes at many points over many years to eliminate these components. Once accomplished, such changes would be equally difficult to reverse. Furthermore, such recommendations fall disproportionately on a few commodities most notably dairy fats. Dramatic alterations in dairy consumption carry much more impact on dietary intakes than simply total fat, saturated fat and cholesterol. While it is becoming possible to alter the basic production of milk and dairy products and to envision a dramatically different milk fat composition, such steps will be difficult and expensive. Hence, it is appropriate to ask whether the data in support of this conclusion are complete and if indeed a finite intake of milk fats are beneficial to overall health. Mammalian milks, including human milk contain 50% of their total fatty acids as saturated fatty acids. Adding a single double bond is a relatively straightforward process already active within the mammary gland. Darwinian selective pressure therefore chose to maintain a significant content of saturated fatty acids in milk. Is it possible evolution found benefits to saturated fatty acids that current recommendations do not consider? Furthermore, milk does not contain simply saturated triglycerides as a bulk fat, but rather a conspicuous range of different fatty acids varying in chain length and unsaturation. Milk is present as highly complex globules with structural properties distinct from other biological sources of fats. In particular, there are complex phos-pholipids making up a highly glycosylated and protein embedded plasma membrane around each milk fat globule. Milkfat is thus a source of bioactive lipids provided as highly absorbable ensembles also serving as an important delivery medium for nutrients, including the fat-soluble vitamins. While very few studies have examined the nutritional consequences of these structures and compositions, their emergence through evolution implies that they provide distinct benefits to individuals consuming them.