Soy milk is a popular dairy alternative in the West, and it has long been a traditional beverage in China, Japan and other parts of Asia. Some people opt to drink soy milk because they are lactose intolerant or lactose sensitive, while others drink it for ethical reasons (such as an interest in animal welfare or in reducing your environmental footprint by eating lower on the food chain) or health reasons (such as wanting to reduce cholesterol intake or eat lower on the food chain).
The health benefits of soy milk are controversial, in part because (like milk) soy is a common food allergen. However, it is generally accepted that soy milk is a healthy alternative to cow's milk and many believe that soy milk is healthier than dairy milk.
Fat, Cholesterol and Protein in Soy Milk vs. Cow's Milk
In large part due to the milk industry's ad campaigns about how healthy milk is, many people wrongly assume that all milk is healthy. However, only low-fat and fat-free milk are accepted as 'healthy' by the medical community.
Unlike cow's milk, soy milk is naturally low in fat. Regular-fat soy milk contains slightly more fat per cup than 2% milk, but it is naturally free from saturated fat (which is considered to be more unhealthy than unsaturated fat). (More on fat contents in milk)
Because it is made from plant material instead of an animal byproduct, soy milk contains no cholesterol. Dairy milk contains about 20 milligrams of cholesterol per cup. An adult's recommended daily allowance of cholesterol is 300 milligrams, though many Americans consume far more, and many people with high cholesterol or some types of heart problems are better off consuming well below the usual RDA of cholesterol.
Soy milk is also high in protein. One cup of soy milk contains about seven to ten grams of protein. This is similar to cow's milk, which contains eight grams of protein per cup. Although some sources say that soy protein in soy milk is undigestible or an incomplete protein, this is not true. Soy milk protein is a complete protein and is highly digestible.
Health Benefits of Fortified vs. Unfortified Soy Milk
When used as a cow's milk replacement, unfortified soy milk is lacking in calcium and B vitamins (especially vitamin B12). For this reason, many soy milk brands on the market are fortified with calcium and B vitamins, as well as vitamins E and D.
Soy Milk and Calcium
One of the main drawbacks of soy milk as a milk replacement is its lower level of calcium. Unfortified soy milk contains about one-fourth the amount of calcium in milk. Fortified soy milk is often comparable to cow's milk in its calcium levels, but some studies show that fortified calcium may not be as healthful as naturally occurring calcium.
For vegans and people who are lactose intolerant, the issue of calcium should be addressed through a more comprehensive dietary plan involving alternate sources of calcium (such as almonds, beans, leafy greens and, for people who are not vegan, sardines). For people who use soy milk as a healthy source of isoflavones but who do not object to dairy in their diets, calcium is also available from cheese, yogurt and other dairy products.
Hormones in Soy Milk vs. Cow's Milk
As with dairy milk, there is some controversy over the hormones in soy milk. Cow milk naturally contains estrogen and progesterone. Cows are milked throughout pregnancy in the United States, and their hormone levels peak near the end of their term. Some studies have linked the consumption of cow's milk with various types of cancer and early sexual puberty. Additionally, cows in the U.S. are sometimes treated with rBST or rBGH, types of controversial growth hormones that studies have linked to various cancers.
Soy milk naturally contains isoflavones. Isoflavones act in a manner similar to the hormone estrogen (but are not actually estrogen). They are phytoestrogens or plant-derived compounds with 'estrogenic activity.' Some studies have linked high consumption of these compounds with reduced or increased chances of breast cancer, but there is no conclusive evidence either way. The consumption of abnormally high levels of isoflavones is questionable, but regular consumption of soy milk and other sources of isoflavones is considered to be healthy.
