Soy milk and nonfat milk are both low in fat and high in protein. They are also both equivalently good sources of calcium and additional vitamins and minerals, provided the soy milk is fortified. Soy milk has a longer shelf life than liquid milk, which makes it a more economical choice if you are not a big milk drinker. While the shelf life of nonfat milk is generally a little over one week, soy milk is best consumed within 14 days of opening.
Calories and Sugar
The calories in one 8-oz. cup of soy milk depend on whether it is sweetened. One 8-oz. serving of soy milk can have from 80 to 130 calories, the difference being the amount of sugar it contains which ranges from 5 to 12g sugar. By comparison, nonfat milk has a consistent 90 calories per 8-oz. serving. Nonfat milk has 12g sugar per serving, which includes the natural sugar lactose. Flavored milk may have added sugar and more calories.
Fat and Protein
Both soy milk and nonfat milk are low in fat and high in protein. An 8-oz. cup of soy milk contains 3.5g fat comprising mainly healthy unsaturated fats. An 8-oz. cup of nonfat or fat-free milk, by definition, contains less than 0.5g fat per serving. Nonfat milk can have from 8 to 9g protein per serving, whereas soy milk has 7g protein per 8-oz. serving. The protein in soy milk is complete in that it contains trace amounts of all essential amino acids. Milk protein is also complete, containing trace levels of all essential amino acids however it is especially high in glutamic acid and leucine.
Vitamins and Minerals
Both nonfat milk and soy milk require fortification to put it on par with whole milk, nutritionally. Soy milk must be fortified by calcium and water-soluble B vitamins, and nonfat milk must be fortified with fat-soluble vitamins A,D, E and K to bring it back into range of low-fat, reduced-fat or whole milk as a good source of these vitamins. Whereas soy milk is conventionally fortified with powdered supplements, nonfat milk often has milk solids added back in which contain vitamins and minerals. Both an 8-oz. serving of nonfat milk and, when fortified, an 8-oz. serving of soy milk provide approximately 30 percent of the recommended daily allowance for calcium or 300mg. Each provide 15 percent of the RDA for riboflavin, vitamin B-12 and vitamin A. Soy milk provides 24mg folate per serving, double the folate in nonfat milk. Nonfat milk is a better source of potassium, providing 400mg per 8-oz. cup.
Health and Ethics
People often choose between soy milk or nonfat milk for health or ethical reasons. People with lactose intolerance may not tolerate any cow's milk because it upsets their digestive system. Others, looking to lower dietary cholesterol or saturated fat, may not like the watered-down flavor of nonfat milk but find the smooth quality of soy milk acceptable. Vegetarians may prefer soy milk for religious or ethical reasons. Both soy milk and nonfat milk are sold in a range of flavors, including some with added sweetener to make them more palatable to children.
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