By Mohammad Ahrar, PhD
Introduction
Milk is formed in the mammary glands of mammals for the purpose of sustaining the life of their young during their early life. Mother’s milk provides all the required nutrients for a newborn. Because of the rich nutrients in milk, it has been used by modern man as a source of food. The most commonly consumed types of milk in recent eras come from cows, sheep, and goats. Western countries drink cow’s milk most frequently and this article focuses on cow’s milk and dairy products derived from cow’s milk.
Nutritional Value of Milk
It is well documented that milk contains a wide array of nutrients, including vitamins, minerals, protein, and fat which are needed by the human body. Drinking milk has long been associated with healthy bones due to its powerful combination of nutrients, such as calcium, phosphorus, potassium, protein, and Vitamins A and D. All of these nutrients are essential for maintaining healthy bones.
Calcium
Approximately 99% of your body’s calcium is stored in your bones and teeth. The minerals found in milk—calcium, potassium, and magnesium—help maintain strong bones, proper muscle functioning, and fluid balance in the blood and tissues. Age-related bone loss is most marked in postmenopausal women, but also occurs in men. Studies have linked consumption of milk and dairy to a lower risk of osteoporosis and fractures, especially in older adults. For more information about calcium, please visit Peyk #175.
Vitamin D
Milk is a good source of vitamin D. Milk is often fortified with vitamin D for its beneficial role. The primary role of Vitamin D is to support the development and maintenance of bones and teeth and it also helps maintain the normal level of calcium in the blood. Vitamin D is necessary for the absorption of calcium and phosphorus by the small intestine and to reclaim calcium from kidney tubules that would otherwise be excreted in the urine. The health benefits of Vitamin D are discussed in Peyk #170.
Vitamin A
Milk, especially whole milk, contains a fair amount of Vitamin A. This vitamin is best known for its role in normal vision, gene expression, reproduction, embryonic development, growth, and immune system functioning. For more information about Vitamin A, please visit Peyk #169.
B Vitamins
The B vitamins found in milk—such as Vitamin B2 (riboflavin), Vitamin B3 (niacin), and Vitamin B12 (cyanocobalamin)—share a role in energy production as coenzymes to make energy available to the cells for normal chemical reactions. Additionally, Vitamin B2 has antioxidant properties and can fight free radicals to help prevent some of the damage they cause. It is also important for growth and red blood cell production. Vitamin B3 plays a role in repairing damaged DNA and also acts as an antioxidant. Vitamin B12 helps build red blood cells and has a role in maintaining the central nervous system. More information about the B vitamins is discussed in Peyk #174.
Milk Proteins
Protein is necessary for many functions in the body, including growth and development, cellular repair, and immune system regulation. It is also the key nutrient for bone health and muscle formation and functions. Milk is known as an excellent source of high-quality protein, meaning it contains all nine of the essential amino acids necessary for synthesizing proteins and enzymes that allow the body to function at an optimal level. Older adults need good-quality protein in their diet to prevent or delay the age-related loss of muscle mass and strength, known as sarcopenia. Consumption of milk and milk products has been linked to greater muscle mass and better physical performance in older adults. Several studies have demonstrated that drinking milk after a workout can decrease muscle damage, promote muscle repair, increase strength, decrease muscle soreness, and lower the risk of age-related muscle loss. Detailed information about proteins is discussed in Peyk #162.
Types of Milk Proteins
There are two main types of protein found in milk — casein and whey protein. Both are considered high-quality proteins.
Casein makes up the majority of the protein found in cow’s milk, comprising 70 ـ 80% of the total protein content. It is this protein that remains in cheese and most fermented dairy products. Casein is a complete protein and contains all of the essential amino acids necessary for the synthesis of body proteins and general health.
Whey is a liquid that separates from milk during cheese production. It contains lactose and protein plus some other nutrients. Whey protein accounts for around 20% of milk protein. Whey protein contains the branched-chain amino acids leucine, isoleucine, and valine, all of which may be particularly helpful in building muscle, preventing muscle loss, and providing fuel during exercise. The branched-chain amino acid leucine in whey is the most important growth-promoting (anabolic) of all amino acids. For this reason, whey protein is effective for the prevention of age-related muscle loss, as well as for improved strength. Besides, whey protein is very digestible and easily absorbed in the small intestine compared with other types of proteins. The high quality of whey protein makes it one of the best dietary sources of protein for bodybuilders, athletes, and others who want additional protein in their diet.
Benefits of Milk Proteins
Chronic inflammation is a risk factor for many diseases (explained in Peyk #185). Studies have found that high doses (greater than or equal to 20 grams/day) of whey protein supplements significantly reduced C-reactive protein (CRP), a key marker of inflammation in the body.
Reports show that consuming fermented milk products seems to lower blood pressure, reduce diarrhea, and have some antioxidant and immune-stimulating effects. One study with a large group of overweight individuals showed that whey protein supplementation lowered systolic blood pressure by 4%. Other milk proteins (casein) have also been shown to have similar effects. This study is also supported by another study that found significant effects when participants were given whey protein concentrate (22 g/day) for 6 weeks. For more information about controlling blood pressure, please visit the medical article by Dr. Sanaz Majd in Peyk #202).
Dairy Products
Yogurt is the most common dairy product in Middle East countries. Dairy products such as yogurt and cheese and other fermented milk products are usually made by adding different types of bacteria to milk. The acid-forming bacteria such as Lactobacillus acidophilus and Streptococcus lactis convert lactose into lactic acid which gives a sour taste to yogurt and some cheeses. Some other bacteria, such as Lactobacillus bulgaricus, add flavor and a unique taste to dairy products.
Butter is made by churning fermented milk products such as yogurt and collecting its fat portions, the butter. Salt may or may not be added to butter.
It is important to know that dairy products contain saturated fat. Milk products also contain cholesterol. Some types of cheese contain 70 percent fat. Some studies report that diets high in saturated fat and cholesterol increase the risk of heart disease. The American Heart Association still recommends adults stick to fat-free or low-fat dairy products. However, new research suggests that full-fat dairy might not be much of a threat to heart health. The reason is that milk fat, in contrast to beef and pork fats, contains short-chain fatty acids that are mostly converted to energy rather than accumulated as fat in different organs of the body. More information about fats and cholesterol is explained in Peyk ##159, 161, and 201.
Consumption of Dairy Products and Health Effects
The United States Department of Agriculture (USDA) provides “Choose My Plate” recommendations, including that adults should consume 3 servings of dairy products per day as a nutrient-dense food. Children should consume around 2 or 2.5 servings per day, depending on their age. A typical serving of dairy includes 1 cup of milk.
Milk consumption is a debated topic and controversial in the nutrition world. Some research warns against consuming too much dairy, while other studies show some benefits from regular dairy consumption.
A report by the Harvard Medical School looked at 20 studies involving almost 25,000 people and found no association between the consumption of most dairy products and cardiovascular disease. The exception was too much consumption of milk, a liter a day, which was linked with a higher risk of cardiovascular disease. A study involving 2,000 men, published by the British Journal of Nutrition, found that those who ate plenty of fermented dairy products such as yogurt had a smaller risk of coronary artery disease than men who ate less of these products. And a report from the National Library of Medicine indicates that the intake of milk and dairy products may protect against the most prevalent chronic diseases, whereas very few adverse effects have been reported.
However, some sources warn against the consumption of milk and dairy products due to their saturated fat contents contributing to heart disease, type 2 diabetes, and Alzheimer’s disease. Studies have also linked the high-fat content and hormones in milk, cheese, and other dairy products to some kinds of cancers. However, the exact causes were not explained and many studies do not support these findings.
Lactose Intolerance
Infants and children produce enzymes that break down lactose, the sugar found in milk, but as we grow up, many of us lose this capacity. Genetics may have something to do with it, too. Lactose intolerance affects around 65% of the world’s population, ranging from 15 percent of Caucasians, 74 percent of Native Americans, to 95 percent of Asian Americans. People who are lactose intolerant do not produce the enzyme lactase to break down lactose into the simple sugars of glucose and galactose. Therefore, undigested lactose can irritate the small intestine and can cause severe digestive upset and diarrhea.
Summary
Milk contains a wide array of nutrients, including vitamins, minerals, protein, healthy fats, and antioxidants, and drinking milk has been associated with healthy bones due to the combination of nutrients, such as calcium, phosphorus, potassium, protein, and Vitamins A and D. When it comes to overall health benefits, moderate consumption of milk (except for those with lactose intolerance) and dairy products can provide some of the vital nutrients you need.
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