Milk is a bundle of nutrients, all contained in a nondescript white liquid.
Although milk’s presence as a beverage at meals may not be as popular as it used to be, milk is used in many products that are consumed throughout the day.
On the Food Guide Pyramid, milk and dairy products are placed near the top because, although they are part of a healthful diet, they should be consumed in moderation. Adults should consume 2 servings of low-fat or nonfat dairy products daily; 1 serving equals 1 cup of milk or yogurt or 1 1/2 ounces of cheese. Children and pregnant or lactating women should add an extra serving each day. Milk and other dairy foods are rich in calcium, a mineral important for developing strong bones and teeth and for nerve transmission. They are also an important source of many vitamins and minerals. Large quantities of these foods, however, are not needed to ensure that you are getting adequate amounts of these nutrients. Just three 8-ounce glasses of skim milk, for example, provide nearly all of the calcium you need each day.
Some people do not include enough dairy foods in their diets. One reason is the mistaken belief that all dairy products are high in fat. Some are, but there is an abundance of low-fat and nonfat dairy products, from milk to yogurt to cheese.
Other people do not consume dairy foods because of intolerance to milk sugar or allergy to milk proteins. However, those with intolerance to milk often do not need to follow a diet that is completely milk-free (see sidebar: Lactose Intolerance, page 347). People with allergy to milk must avoid dairy foods and may want to get help with adjusting their diets to ensure nutritional adequacy (see sidebar: Milk Allergy: Hidden Ingredients, page 349).
Another reason people do not consume dairy products is the growing consumption of soda pop. The average American drinks about a half gallon of milk a week but, in comparison, about 11 cans — or a gallon — of soda pop a week. Taking calcium supplements or eating calcium-enriched food can help you obtain needed calcium, but dairy foods are an easy way to get the calcium and other essential nutrients you need.
Basics
Milk can be consumed in its fluid form, in a more solid form (such as yogurt), as cheese, or as a major ingredient that is added to other foods. Dairy cases now abound with milk-based products and their reduced-fat and nonfat versions. The cornucopia of dairy products includes the following:
Fluid milk — Although cow’s milk is generally consumed in the United States, other cultures use milk from goats, camels, llamas, reindeer, sheep, and water buffalo. Milk is a staple in diets worldwide.
Dried and concentrated milk — These products include powdered milk, evaporated milk, and condensed milk.
Cheese — Cheese is made by coagulating and draining milk or cream or a combination of both.
Yogurt — Yogurt is made by adding bacteria to milk to ferment it.
Ice cream and other dairy desserts — Ice cream and other frozen desserts are simply milk or cream to which sugar, flavorings, and, often, eggs have been added.
Cream and sour cream — Cream is the fat that rises to the top of the surface in unprocessed milk. Sour cream is simply cream that has been fermented or thickened. The cream is usually "soured" by adding bacteria to it, much in the way that yogurt is created.
Butter — This yellowish substance is essentially fat that has been separated from cream. For that reason, it is discussed in Fats, Oils, & Sweeteners, page 389.
Processing of Milk and Milk Products
Virtually all milk and milk used in dairy products is pasteurized. Pasteurization is a process invented by French chemist Louis Pasteur. It uses heat to destroy harmful bacteria in milk, but it retains the nutritional value of milk.
Pasteurization kills bacteria that have been responsible for major plagues such as tuberculosis, polio, scarlet fever, and typhoid fever. It is also advantageous because it destroys many of the bacteria that cause spoilage and many of the enzymes that promote rancidity. Pasteurization, therefore, increases both shelf life and safety of milk.
A common term that consumers see when purchasing milk is "homogenized." Homogenization is a process introduced in the 1950s in which fat globules in the milk are broken down so they are evenly dispersed throughout the milk. Most milk at the supermarket is homogenized.
During homogenization, milk is forced through a small opening at high pressure. The product has a smoother, richer texture and a whiter color than nonhomogenized milk.
Nutrition
Milk and dairy products provide many of the key nutrients needed daily, particularly calcium (for more specific information, refer to milk in the nutrient table on page 472).
Milk and dairy products also supply high-quality protein. Because of its animal source, milk protein is complete — meaning it provides a sufficient amount of the nine essential amino acids.
Dairy products are also naturally rich in B vitamins and most of the minerals considered to be essential in the diet, including calcium, magnesium, phosphorus, zinc, iodine, and selenium. In addition, milk also contains several vitamins and minerals that have been added to meet the requirements of the Food and Drug Administration. Low-fat and nonfat milk may be fortified with vitamin A because this fat-soluble vitamin is lost when the milk fat is removed. Vitamin D is added to all milk to help the body better use calcium.
Milk also is a good source of carbohydrates. With the exception of cheeses and butter, milk products are higher in carbohydrates than protein or fat. Milk’s carbohydrate is lactose, a sugar unique to milk that is actually two sugars (glucose and galactose) linked together. Food scientists call this type of sugar a "disaccharide."
Lactose is not as sweet as other sugars. It helps the body absorb calcium and phosphorus and may even help in the growth of friendly bacteria needed in the intestines. In addition, galactose, one of the sugars in lactose, is a vital part of brain and nerve tissue. It is released when the body digests lactose. Lactose is a bit of a paradox, however. Although it has these beneficial properties, many people have difficulty digesting milk (see sidebar: Lactose Intolerance, page 347).
Lactose Intolerance
As many as 50 million Americans are estimated to have lactose intolerance — an inability to adequately digest ordinary amounts of dairy products such as milk and ice cream.
Worldwide, nearly 70 percent of the adult population is thought to be lactose intolerant, and the condition is very common among American Indians and those of Asian, African, Hispanic, and Mediterranean descent.
Lactose is the sugar that is naturally present in milk and milk products. It must be broken down by lactase (an enzyme found in the intestine) before the body can use it. If there is not enough lactase, undigested milk sugar remains in the intestine. Bacteria in the colon then ferment this sugar. Gas, cramping, and diarrhea can follow.
Most of us begin to lose intestinal lactase as we age. However, this occurs to varying degrees. Thus, people with lactase deficiency vary in their ability to comfortably digest milk and milk products.
As obvious as the symptoms of lactose intolerance may be, it is not easily diagnosed from the symptoms alone. Many other conditions, including stomach flu and irritable bowel syndrome, can cause similar symptoms.
See your physician to determine whether you are lactose intolerant. Measurement of the hydrogen in your breath after you have taken in lactose is a useful test because large amounts of hydrogen indicate that lactose is not being fully digested and that you are probably intolerant.
Persons with milk allergies should avoid milk, but those with lactose intolerance often do not need to follow a diet that is completely lactose-free. The following suggestions may help:
• Avoid eating or drinking large servings of dairy products at one time. (Several smaller servings over the course of a few hours are much easier to digest.)
• Drink milk or eat dairy products with a meal.
• Choose hard or aged cheeses, such as Swiss or cheddar, over fresh varieties. Hard cheeses have smaller amounts of lactose and are more likely to be tolerated.
• Take lactase tablets or drops, such as Lactaid or Dairy Ease. These types of products contain the enzyme that breaks down lactose, reducing the amount that your body must digest on its own.
For help with meal planning, you may want to see a registered dietitian.
Despite all the nutrients in milk, the nutritional advantages of dairy products must be weighed against the potential health drawbacks of two key components in milk: sodium and fat. Whole milk, cream, and cheeses contain substantial amounts of fat, especially saturated fat. These fats add calories and have been tied to higher cholesterol levels and cardiovascular disease.However, it is important to note that low-fat and nonfat milk varieties are available and are significantly lower in fat than whole milk. In addition, depending on how much is consumed, milk or products made from milk may be a major source of sodium — a special concern for anyone following a low-sodium diet.
Selection
Unless dried or canned, milk and dairy products are perishable. For that reason, most have an expiration date printed on the packaging. The date often states, "Sell by . . ." and is a good indicator of freshness. Look for the date before buying and before consuming a product. Usually, dairy products will keep about a week beyond that date.
Storage
Keep milk in the coldest part of your refrigerator. Avoid storing milk in the refrigerator door unless it has a special compartment designed to keep the milk colder than in the rest of the refrigerator.
Keep yogurt and fresh cheeses in airtight containers in the refrigerator. Loosely wrapped, these foods will pick up smells in the refrigerator, possibly leaving them with an undesirable taste.
Cheeses such as cottage cheese, ricotta, and cream cheese will keep for 1 week after the sell-by date. Soft cheeses — such as Brie, Camembert, Muenster, and mozzarella — and blue-vein cheeses can keep from 1 to 3 weeks. Semi-firm and hard cheeses, such as cheddar and Monterey Jack, will keep as long or longer. Generally, the harder the cheese, the longer it will remain fresh when carefully stored.
Shredded cheese will not keep as long because it has more surface exposed to the air. Soft cheese that has mold on it should be discarded. Firm cheese that has mold can sometimes be used as long as 1/2 inch to 1 inch of cheese near the molded spot has been cut away and discarded. If any milk or milk product has a strange odor, throw it out.
Safety Issues
Some small markets or independent farmers still sell raw milk. Because it has not been pasteurized, this milk may contain germs that make you ill. For that reason, the sale of raw milk is often prohibited by law, depending on location.
For some people, proteins in cow’s milk may trigger allergic reactions. Whey proteins (beta-lactoglobulin and beta-lact-albumin) and casein are the primary proteins that trigger allergic reactions. Symptoms of a milk allergy may include nasal congestion, hives, itching, swelling, wheezing, shortness of breath, nausea, upset stomach, cramps, heartburn, gas or diarrhea, light-headedness, and fainting.
It is easy to confuse a milk allergy with another common health concern related to dairy foods — lactose intolerance. Lactose intolerance (see page 347) also can lead to nausea, vomiting, cramping, and diarrhea. However, if you have lactose intolerance, you usually can eat small amounts of dairy food without problems. In contrast, a tiny amount of a food to which you are allergic can trigger a reaction.
If you suspect that you have any food allergies, see your physician. You may then be referred to an allergist for a careful evaluation. This generally includes a medical history, physical examination, and skin or blood testing. If the diagnosis is a milk allergy, it is essential to eliminate milk and foods made with milk from your diet (see sidebar: Milk Allergy: Hidden Ingredients, page 349).
