Oat Milk vs Soy Milk: A Dietitian’s Comparison

With concerns about the negative impacts of the dairy industry on animal welfare and our environment, many people are turning to non-dairy alternatives. If you’re unfamiliar with plant-based milks, you may have no clue where to start. 

Oat milk and soy milk are two popular options, but is one healthier than the other? What are the best uses for each?

As a vegan registered dietitian who knows a thing or two about thriving without dairy, I’ll compare oat milk vs soy milk and provide my tips for choosing between them.

What is oat milk?

Oat milk is a dairy-free milk alternative made from oats, a popular grain. Oat milk is produced by:¹ 

1. Blending oats with water
2. Adding enzymes to break the natural carbohydrates down into smaller sugars (a process known as hydrolysis)
3. Adding vitamins and minerals
4. Killing harmful bacteria through pasteurization

The process may vary slightly depending on the brand. For example, not all brands fortify their oat milk with vitamins and minerals or use hydrolysis to break the carbohydrates down into simpler sugars.

RELATED:  Oat Milk vs. Rice Milk – Is One Healthier?

What is soy milk?

Soy milk is a nutritious non-dairy beverage made from soybeans and water. It’s made by:

1. Soaking soybeans in water
2. Grinding soybeans with additional water
3. Boiling the soybean-water slurry to improve its nutrition and flavor and to kill bacteria
4. Filtering out the fiber-rich solids
5. Adding vitamins and minerals 
6. Killing harmful bacteria through pasteurization

As with oat milk, vitamin and mineral fortification is done by some brands and not by others.

Oat milk vs. soy milk nutrition 

Oat milk and soy milk are both dairy-free alternatives to cow’s milk, but they have some important differences in the nutrition they provide. 

To see how oat milk and soy milk stack up nutritionally, let’s compare two popular brands: Oatly Original Oatmilk and Silk Organic Unsweetened Soy Milk.

Remember that the nutritional profile will vary based on the brand, use of vitamin & mineral fortification, and whether the product is sweetened or flavored. 

Per 8-ounce serving, soy milk is a much better source of protein (7 grams) than oat milk (0 grams) and is a little higher in iron. Oat milk tends to be higher in carbohydrates. This makes sense considering soybeans are higher in protein than oatmeal.

Oat milk can also be higher in added sugars if the oats are hydrolyzed. This process breaks natural carbohydrates down into smaller sugars, making the final product creamier and tastier. However, since these sugars act like added sugars in the body, they must be labeled as added sugars on the nutrition label.

This is why Oatly lists added sugars on the nutrition label even though no sweeteners are listed in the ingredients.

Calcium and vitamins A, D, and B12 are often added to both oat and soy milk. The amounts will vary based on how much a brand decides to add to its products, of course, so be sure to read the nutrition facts label for each non-dairy milk.

Ingredients

Let’s take a closer look at the ingredients in these products. 

Oatly Original Oat Milk: Oat base (water, oats). Contains 2% or less of: low erucic acid rapeseed oil, dipotassium phosphate, calcium carbonate, tricalcium phosphate, sea salt, dicalcium phosphate, riboflavin, vitamin A, vitamin D2, vitamin B12.

Silk Organic Unsweetened Soy Milk: Organic Soymilk (Filtered Water, Organic Soybeans), Contains 2% or Less of: Vitamin and Mineral Blend (Calcium Carbonate, Vitamin A Palmitate, Vitamin D2, Riboflavin [B2], Vitamin B12), Sea Salt, Gellan Gum, Ascorbic Acid (Vitamin C To Protect Freshness), Natural Flavor.

As you can see, both contain 98% oats or soy blended with water. Both also contain sea salt and a blend of vitamins and minerals.

Oatly also contains a small amount of low erucic acid rapeseed (canola) oil, likely to provide extra creaminess. 

Silk soy milk contains gellan gum, an emulsifier that provides a creamy, homogenous consistency.

RELATED: Is Canola Oil Vegan? Is It Healthy?

Health implications

Now that we know how these two non-dairy milks compare nutritionally, let’s discuss how they can impact our health. 

Vitamins & minerals

Many varieties of oat milk and soy milk are fortified with vitamins and minerals like calcium, vitamin D, vitamin A, and vitamin B12 to better match the nutrition profile of dairy milk and to better meet the needs of vegans and other individuals who avoid dairy.

Calcium and vitamin D are important for maintaining strong bones and preventing osteoporosis, while vitamin B12 can help vegans avoid the severe neurological impairments that can result from a B12 deficiency.

All in all, the best thing to do is to check the nutrition label on any oat milk or soy milk product you’re considering and make sure they’ve been fortified with calcium and vitamin D at a minimum. 

It’s also a good idea for vegans to choose one fortified with vitamin B12.

Blood sugar management

For most people, the amount of added sugars present in oat milk made from hydrolyzed oats isn’t a huge concern. While it’s a good idea to limit your intake of added sugars, the amounts in oat milk likely won’t cause you any harm as long as you aren’t overdoing it on sweets elsewhere in your diet.

That said, if you have type 2 diabetes and struggle to keep your blood sugar at a healthy level, you may need to be more careful with your choice of non-dairy milk. The following tips can help:

• Choose oat milk with fewer added sugars (Califia Farms, Elmhurst 1925, and Planet Oat are fairly low)
• Consume oat milk with a source of protein and fiber, as in a protein smoothie or oatmeal with nuts, rather than on its own
• Choose an unsweetened, higher-protein milk like soy or pea milk

Polycystic ovary syndrome (PCOS)

Interestingly, soy milk may be a more helpful choice for individuals with PCOS. 

A small 2020 study² found that women with PCOS who drank a chocolate soy milk beverage twice a day for three days showed better improvements in fasting glucose, fasting insulin, and insulin sensitivity compared to the control group.

The authors suggested this result may be thanks to the anti-inflammatory isoflavones found in many soy products.

Good for lactose intolerance

Oat milk and soy milk are both lactose-free, making them excellent choices for people with lactose intolerance.

Culinary uses

Taste 

Oat milk is a little sweeter than soy milk thanks to its higher carbohydrate content, especially when made from hydrolyzed oats. Overall, it has a mild, neutral taste that doesn’t interfere with other flavors.

Soy milk with a mild bean-y flavor that, while not unpleasant, may take some getting used to especially if you want to drink it straight. I’ve found that when blended in a smoothie or used in cooking and baking, the flavor isn’t noticeable.

Texture 

Both of these non-dairy milks are smooth and creamy. They also come in “barista blend” varieties which are even creamier. 

Best uses

Oat milk and soy milk both have a smooth, creamy texture and mild flavor, making them great choices for:

• Adding to tea or coffee
• Using in place of dairy milk in baked goods
• Mixing in oatmeal
• Blending in smoothies
• Cooking polenta or grits
• Pouring over cereal
• Hot chocolate
• Waffle & pancake batter
• Non-dairy “cream” sauces for pasta

RELATED: Vegan Tips for Beginners

Sustainability

Plant-based milk of any type is better for the environment than cow’s milk in terms of land use, water use, and carbon footprint. Compared to dairy, oat milk and rice milk are both sustainable options.

That said, oat milk has a slight advantage in terms of its greenhouse gas emissions.

According to a 2022 study³, the greenhouse gas emissions in gram carbon dioxide equivalents associated with the production of a 6.8-ounce glass of cow’s milk, soy milk, and oat milk are as follows:

Dairy milk: 213 CO2 equivalents

Soy milk: 88 CO2 equivalents

Oat milk: 60 CO2 equivalents

While both plant-based beverages are better for the environment than dairy, oat milk has a slight edge.

How to choose between oat milk and soy milk

Unfortunately, there isn’t a clear-cut answer to whether oat milk or soy milk is the better choice for you. I recommend thinking about the following factors when choosing between them:

1. Fortified with calcium, vitamin D, and vitamin B12. Choosing fortified non-dairy milk is one of the easiest ways for vegans to get enough calcium and vitamin D to support bone health and enough B12 to prevent neurological issues.
2. Added sugars. If you can, choose unsweetened or “zero sugar” varieties. A small amount of added sugar in the context of an overall healthy diet isn’t a big problem, but it can add up throughout the day.
3. Sustainability. While both are more environmentally friendly than dairy milk, the production of oat milk has a slightly lower carbon footprint than soy. This may influence your choice depending on how highly you prioritize sustainability.
4. Blood sugar management. If you struggle to manage your blood sugar even with a balanced diet, unsweetened soy milk or oat milk with zero added sugars may be a better choice than oat milk made from hydrolyzed oats. For most people, however, the carbohydrate content of oat milk shouldn’t pose a problem in the context of a healthy diet.
5. Protein needs. If you have higher protein needs due to a physically active lifestyle, are trying to build muscle, or struggle to get enough protein from food, choosing soy milk in place of oat milk is a simple way to get more protein.

If purchasing for your family, keep in mind that neither oat milk is not considered an appropriate milk alternative for toddlers and young children due to its low protein content. Fortified soy milk, pea milk, and non-dairy milk with added pea protein are recommended instead.

Summary

Oat and soy milk can both be a nutrient-dense addition to dairy-free diets depending on the formulation. As long as they’re fortified, both are good sources of calcium and vitamin D, key nutrients for vegans and others avoiding dairy. Vitamin B12 is also commonly added.

Soy milk is a better source of plant-based protein, while oat milk has a higher glycemic index and is often higher in added sugars.

If you want the most nutrient-dense option, I’d recommend unsweetened soy milk or another high-protein plant-based milk especially for people who are physically active. But if you know you consistently get enough protein from food or are allergic to soy, fortified oat milk can still provide valuable vitamins and minerals.

Still wondering how to choose the best plant-based milk for your needs? My Guide to Non-Dairy Milk is here to help!

Or check out my other plant-based milk comparisons:

Walnut Milk vs. Almond Milk

Almond Milk vs. Cashew Milk

Oat Milk vs Coconut Milk

Oat Milk vs Soy Milk – FAQs

Which is better for you soy milk or oat milk?

Soy milk tends to be more nutrient-dense than oat milk since it’s higher in protein and often, though not always, lower in added sugars. Both are good sources of vitamins and minerals like calcium, vitamin D, and vitamin B12 when fortified with these nutrients. Not all brands fortify their plant-based milk, so be sure to check for this.

Can I replace soy milk with oat milk?

You can use oat milk as a substitute for soy milk in beverages, smoothies, and most recipes since they both have a creamy consistency and mild flavor. Nutritionally, oat milk has less protein and may contain more added sugars, so it isn’t a direct substitute for soy milk.

The scientific information in this article was accurate at the time of publishing but may change over time as new research becomes available.

References

1. Oatly. Our Process. Oatly website. Accessed 3/4/24.
2. Haudum C, Lindheim L, Ascani A, et al. Impact of Short-Term Isoflavone Intervention in Polycystic Ovary Syndrome (PCOS) Patients on Microbiota Composition and Metagenomics. Nutrients. 2020;12(6):1622. Published 2020 Jun 1. doi:10.3390/nu12061622
3. Singh-Povel CM, van Gool MP, Gual Rojas AP, Bragt MCE, Kleinnijenhuis AJ, Hettinga KA. Nutritional content, protein quantity, protein quality and carbon footprint of plant-based drinks and semi-skimmed milk in the Netherlands and Europe. Public Health Nutr. Published online February 23, 2022. doi:10.1017/S1368980022000453