Oat milk vs cow's milk: close on calories, but different where you'd never expect

Surprise one: the calories aren't as low as you think

Here are the numbers per 100ml. Cow's milk comes from the USDA database, unsweetened oat milk uses typical market figures, which vary a little by brand:

Unsweetened oat milk usually sits between the two cow's milks: more calories than skim, fewer than whole. So if you choose oat milk only because you think it has fewer calories than cow's milk, that's only true next to whole milk.

Surprise two: about a fourfold protein gap

Look at the protein line: 3.4g versus about 0.8g. Cow's milk has about four times the protein.

In a 250ml glass, to make it easy to picture:

• Glass of cow's milk: about 8g protein, close to one and a half eggs.
• Glass of oat milk: about 2g protein, around a third of an egg.

Cow's milk protein is also complete protein, with all the essential amino acids. We say more in complete protein and plant protein.

So oat milk is a drink, while cow's milk is closer to a light snack with protein. Neither is wrong. They just play different roles.

Carbs: similar amounts, but from different "families"

The two glasses have similar carbs, but the sources are completely different:

• Cow's milk: nearly all the carbs are lactose, the natural sugar already in milk. WHO doesn't count the lactose in milk as free sugar.
• Oat milk: the carbs come from oat starch, and some of it may have turned into sugar during processing. Details in how oat milk is made, and what's in it.

Lactose is the key point for many Vietnamese people. To digest lactose, your gut needs an enzyme called lactase. In most Asian adults, lactase levels drop after early childhood. Drink a lot of cow's milk at once and they may feel bloated or hear a rumbling tummy.

This is very common and usually nothing to worry about. Many people can still handle a small amount, or find yogurt and cheese easier because some lactose is already gone. Oat milk has no lactose, which makes it a comfortable pick for anyone who often feels off after cow's milk.

Calcium: a question for the label

Cow's milk comes with calcium built in, about 110 to 120mg per 100ml, and the body absorbs it well.

Oats don't naturally contain much calcium. Many big oat milk brands add calcium, vitamin D and vitamin B12 to get closer to cow's milk. Some don't.

So here's a simple rule: if the label doesn't say calcium-fortified, don't count on your plant milk to replace the calcium in cow's milk. Top up calcium from other foods like tofu, small fish eaten bones and all, and leafy greens. See also calcium-rich foods besides milk.

What about the environment?

A large 2018 study in the journal Science compared the environmental footprint of dozens of foods. Per liter, plant milks, including oat milk, produced far fewer greenhouse gas emissions and used far less land than cow's milk.

This isn't a nutrition point, but it's a reason many people choose oat milk. We think it's worth knowing as you weigh your options.

So which glass?

And you can absolutely have both. Cow's milk in the morning alongside a low-protein breakfast, oat milk in your afternoon coffee. For a comparison with soy and almond milk, read which plant milk to choose.

Frequently asked questions