Regular cows' milk and soy milk are both packed with nutrients and are fairly interchangeable. However, some people have a difficult time tolerating cows' milk, and soy milk isn't for everybody. In many cases, taste preference or the presence of a cows' milk allergy, lactose intolerance or a soy allergy determines which milk is a better choice for you.
Low-fat cows' milk and soy milk contain similar amounts of essential nutrients. Each type of milk provides about 8 grams of protein per cup and is rich in, or fortified with, calcium, phosphorous, vitamin A, vitamin D and vitamin B-12. With the exception of skim milk, cows' milk contains saturated fat and cholesterol, while soy milk does not. In fact, soy milk is a source of heart-healthy omega-3 fatty acid alpha-linolenic acid, or ALA.
Calorie Content and Weight Control
Cows' milk generally contains more calories than soy milk. A cup of 1-percent cows' milk provides just over 100 calories, but a cup of original soy milk contains just 80 calories. Light soy milk often provides just 50 calories, but skim cows' milk generally contains 90 calories. If you choose whole cows' milk, you'll be getting about 150 calories per cup.
Though soy milk is generally lower in calories, cows' milk may be the most beneficial when you're trying to lose weight, according to a study published in 2011 in Nutrition, Metabolism, and Cardiovascular Diseases. However, a study published in 2012 in the International Journal of Preventative Medicine found that soy milk appears to help reduce waist circumference.
Which is Heart Healthier?
Both cows' and soy milks might help lower your heart disease risks. A review published in 2014 in Current Nutrition Reports found that milk and milk products, like yogurt and cheese, are associated with lower heart disease risks. In fact, authors of this review suggest that even full-fat dairy foods containing saturated fat may protect against heart disease. Another study published in 2007 in the Journal of the American College of Nutrition found that soy milk helps reduce low-density lipoprotein (LDL) cholesterol, which is your bad blood cholesterol.
Which Helps Build Muscle?
Cows' milk and soy milk are both effective for muscle building if you resistance train regularly. These two milks are both sources of complete protein, and contain all of the essential amino acids your body needs to build muscle. However, whey protein found in cows' milk appears to be more effective than soy protein at promoting muscle gains, according to a study published in 2013 in Journal of the American College of Nutrition.
A few potential concerns may help you determine which milk is the best choice for you. If you have a cows' milk allergy, soy milk may be your best bet. If you're lactose intolerant, try lactose-free cows' milk or soy milk. MedlinePlus suggests steering clear of soy milk if you have a soy allergy or gout -- but if you suffer from hot flashes soy may help relieve your symptoms.
An experienced health, nutrition and fitness writer, Erin Coleman is a registered and licensed dietitian and holds a dietetics degree from the University of Wisconsin-Madison. She also has worked as a clinical dietitian and health educator in outpatient settings. Erin's work is published on popular health websites, such as TheNest.com and JillianMichaels.com.