Lipids and Milk

Lipids make up between 3 and 5 percent of cow's milk, with the remainder water, protein, lactose, vitamins and minerals. Milk fat is a rich source of energy, nourishing not only calves but also humans. The nature of the lipids in cow's milk affects the properties of milk-based products such as cheese and butter. In addition, the characteristics of milk lipids may also have implications for your health. Seek the advice of a dietitian or your health care provider with specific concerns about your consumption of dairy fats.

Types

Up to 98 percent of the fat in cow's milk exists as triglycerides, molecules containing three fatty acids and a glycerol, states Helena Mansson in the June 2008 issue of "Food & Nutrition Research." About 2 percent is a type of lipid called diacylglycerol, with less than 0.5 percent as cholesterol. Although more than 400 different fatty acids make up the triglycerides in milk, only 15 fatty acids are present in significant amounts. Of these, 70 percent are palmitic, myristic and stearic acids, all saturated fatty acids. Another 25 percent are monounsaturated fatty acids. Most of the remaining fatty acids in milk fat are the polyunsaturated linoleic and linolenic acids, also known as omega-6 and omega-3 fatty acids.

Digestion and Absorption

The bulk of milk triglyceride digestion begins in your small intestine, where the lipids meet a substance called bile, secreted from your gallbladder. The mixing of bile with milk lipids emulsifies the fats, making them more water-soluble. This effect allows lipase, a digestive enzyme, to break apart the triglyceride into glycerol and its three fatty acids. The epithelial cells of your small intestine then absorb these fat components. Once inside the cell, they convert back to a triglyceride and become incorporated, along with cholesterol, into a transport structure called a chylomicron. Lymph vessels near the small intestine epithelial cell take up the chylomicron and transport it to your blood, where its contents are released.

Implications

The amounts and specific types of fatty acids in milk fat may vary depending on factors such as the breed of cow and components of the cow's feed. These different fatty acids contribute to different flavors of cheeses as well as the composition of various milk products. The types of fatty acids you consume may also affect your health. For example, consuming food rich in milk lipids, such as butter, cream and full-fat cheeses, may raise your blood levels of low-density lipoproteins and cholesterol, so-called "bad" fats that increase your risk for cardiovascular disease.

Other Considerations

Although milk lipids contribute to the richness and flavor of many foods, limiting your consumption of these types of fatty acids may improve your health. Low-fat milk products, including skim milk, reduced-fat cheese and yogurt, supply your diet with high-quality protein and calcium while avoiding the health risks associated with high-fat dairy products.