Nothing’s better than a glass of cold milk, especially when chocolate chip cookies are included in the mix. And while humans have been milking cows since 4000 BC, soy milk was only developed in the past 500 years and has since become an alternative to the traditional stuff. But what’s the better option?

Meet the Competitors

Skim milk and soy milk may look pretty similar, but their content can vary quite a bit. Cow’s milk is a better source of calcium, vitamin A, and vitamin C, while soy milk wins in the vitamin D and iron categories. Calorie content varies between brands, but skim milk generaly has about 20 more calories per cup. And while skim milk has traces of fat (around 0.4 grams), soy milk is naturally fat-free. They do have one thing in common, though— and it’s good news for those skinny jeans— studies suggest the calcium in both milks can help accelerate weight lossPreliminary study: soy milk as effective as skim milk in promoting weight loss. Lukaszuk, J.M., Luebbers, P., Gordon, B.A. School of Family, Consumer, and Nutrition Sciences, northern Illinois University. Journal of the American Dietetic Association, 2007 Oct;107(10):1811-4.Calcium and dairy acceleration of weight and fat loss during energy restriction in obese adults. Zemel, M.B., Thompson, W., Milstead, A., et al. University of Tennessee, Knoxville, Tennessee 37996-1920. Obesity research, 2004 Apr;12(4):582-90..

Cow’s milk and soy milk also pack different punches when it comes to protein. Moo Juice contains both casein and whey protein, both great for building muscle. While whey protein is quickly absorbed into the bloodstream, casein is digested more slowly and provides the body with protein for a longer period of time, together providing a mean one-two protein punchSlow and fast dietary proteins differently modulate postprandial protein accretion. Boirie, Y., Dangin, M., Gachon, P., et al. Laboratoire de Nutrition Humaine, Université Clermont Auvergne, Centre de Recherche en Nutrition Humaine. Proceedings of the National Academy of Sciences of the United States of America. 1997 Dec 23;94(26):14930-5.. Soy milk, however, contains only soy protein, since it’s made by processing soybeans. Soy protein has been found to reduce LDL cholesterol (the “bad” kind) and raise HDL cholesterol (the “good” kind)Effect of soy and milk protein supplementation on serum lipid levels: a randomized controlled trial. Wofford, M.R., Rebholz, C.M., Reynolds, K., et al. Department of Medicine, University of Mississippi Medical Center, Jackson, MS, USA. European journal of clinical nutrition, 2011 Sep 28. Doi: 10.1038/ejcn.2011.168.. Trying to build muscle? Beware— one study suggested that milk-based proteins promote greater muscle growth than soy-based proteins when consumed after resistance exerciseConsumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Wilkinson, S.B., Tarnopolsky, M.A., Macdonald, M.J., et al. Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Canada. The American journal of clinical nutrition, 2007 Apr;85(4):1031-40..

While both milks contain essential vitamins and minerals and can help with weight-loss and muscle-gain, each has its own set of potential pitfalls. Soy milk contains phytoestrogens (plant-produced estrogens), which act similarly to estrogen and may decrease fertility in menSoy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic. Chavarro, J.E., Toth, T.L., Sadio, S.M., et al. Human Reproduction, 2008 Nov;23(11):2584-90. Epub 2008 Jul 23.. But good news, guys— there’s no need to say “soy long” to soy milk. Men can consume soy in moderation without worrying about estrogen overload— just don’t consume more than 3 quarts of soy milk per dayEffect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men. Nagata, C., Takatsuka, N., Shimizu, H., et al. Department of Public Health, Gifu University School of Medicine, Japan. Cancer Epidemiology, Biomarkers and Prevention. 2001 Mar; 10(3):179-84.. Of course, there’s also concern over hormones in regular milk, specifically bovine growth hormone (rBGH). Although rBGH appears safe, there’s no definitive proof. Still worried? Try organic or hormone-free milk instead of regular, to avoid ingesting the rBGH hormone.

The Decision

So is it time to say bye-bye to the moo-moo, or see-ya-later to the soy? Good news— this battle is a toss up! Both options have their benefits— and their dangers— but are fine when consumed in moderation. For those who are lactose intolerant, soy milk can be a saving grace. But if not, don’t forget that a glass of dairy packs more protein and calcium than the soy stuff. In the end, it all comes down to the tongue— and perhaps which milk ‘stache looks better.