Oat vs. Soy Milk: Which Is Healthier?

Milk is a refrigerator staple, but cow’s milk isn’t for everyone. Whether you’re lactose intolerant, have a GI condition, or simply don’t like the taste of real milk, you’ve likely tried a few alternative milks in your morning coffee or cereal. 

And as more plant milks are lining grocery store shelves, some have been touted as healthier than others. Soy milk, for instance, draws concern over high isoflavones (phytoestrogen) content. Meanwhile, certain oat milk brands have been dinged for added oils and sugars. 

So how healthy are soy and oat milks? And does one have an edge over the other? We asked a dietitian for the answers. 

First we’ll address soy milk and hormones. No, soy milk does not contain estrogen, but rather, phytoestrogens, or plant estrogens, which have not been shown to affect hormonal balance in men or women. 

“Despite rumors that soy milk’s isoflavones impact hormones negatively, research actually shows they either have no effect or a positive effect on both cancer and heart disease risk in men and women,” says Kelly Jones, MS, RD, CSSD, LDN. 

For example, a 2018 study shows soy consumption may be associated with a reduction in risk of prostate cancer among men. Studies also show soy’s isoflavones may benefit women experiencing hot flashes during menopause.

Turning to nutrition, soy milk has an equal amount of protein per cup as regular milk. Other nutrients from milk—calcium, B12, and vitamin D—are usually fortified in soy milk, although soy does contain some calcium naturally. “The calcium and B12 in dairy milk are present naturally, while vitamin D is fortified,” says Jones. 

She suggests soy milk for cereal, smoothies, or to drink straight up as a way of increasing protein intake for satiety, muscle maintenance, and growth. 

Made popular in coffee shops, oat milk is beloved for its rich and creamy mouthfeel. No other plant milk settles into a cup of coffee or froths a latte in the same dairy-like fashion that oat milk does. 

“Many people enjoy the texture of oat milk, and it may taste a little better in your latte, but it is lower in protein and less likely to be fortified with adequate amounts of calcium, vitamin D, and B12,” says Jones.

Another concern, notes Jones, are additives. Many store-bought oat milks have added oils and sugars to promote that palate-pleasing texture and taste. So you have to read nutrition labels and hunt to find a healthy oat milk. 

And the winner is... soy milk. “Most often this is what I recommend,” says Jones, remarking on soy milk’s solid protein and nutrient profile. 

Oat milk generally offers between one and three grams of protein per serving, while soy milk sits at seven to eight grams. Soy milk is usually fortified with extra nutrients whereas oat milk is often not. However, Jones still recommends checking soy milk nutrition labels to compare calcium, vitamin D, and B12 amounts, as well as sugar content. “Silk is a good bet since it's so widely available,” says Jones. 

But if you’re team oat milk, that’s OK, too! A good happy medium is to use soy milk for larger serving uses (like cereal and smoothies) and save oat milk for splashing in coffee and beverages. And while most oat milks have a lower nutritional profile, there are some rare gems: Califia Farms offers a protein oat milk that’s fortified with eight grams of pea protein per cup, as well as added calcium and omega-3 fatty acids to promote heart health and lower inflammation. Elmhurst is another oat milk brand that’s favored for having no added oils or sugars. And of course, you can always make your own oat milk!