Plant-based milks – ones like oat, soy and almond milk – are getting increasingly popular. In the UK, more than one-in-three people buy them.
One argument lodged against them – especially by dairy groups – is that they’re less nutritious than cow’s milk. It’s one of the reasons they argue that dairy-like terms (such as “oat milk”) should be banned on labels [I looked at this in a previous post]. It’s a valid concern: if we’re going to promote more plant-based diets then we should also make sure we’re not having a negative impact on health and nutrition.
If these products are less nutritious, consumers should know so they can make informed decisions.
In this post, I look at whether this claim is true. How does the nutrition of plant-based milk compare, and is this a problem?
Plant-based milk: less calories, saturated fat, and protein
Let’s compare the nutritional content of these drinks per 200 millilitres (ml) serving.
I’ve taken the nutritional information from products available in the UK. This includes branded items (from companies such as ‘Oatly’ and ‘Alpro’) but also non-branded products at my local supermarket, Tesco. Tesco is a UK equivalent of an Aldi, Carrefour, or Safeway. It makes its own version of popular products, which are often cheaper.
Later I show the comparisons between specific brands and versions of these products. But for now, we’re going to compare cow’s milk with the average plant-based alternative.
In the chart, we see how these milks stack up on calories, protein, fat, sugar and several key micronutrients – Vitamin D, B12 and calcium.
Of course, it depends on the type of cow’s (skimmed, semi, or whole) and plant-based milk you choose, but there are some general principles to go by. Plant-based milks tend to be:
- Slightly lower in calories, unless you’re drinking skimmed cow’s milk;
- Low in protein with the exception of soy milk (we’ll come on to that later);
- Lower in fat – especially saturated fat – with the exception of coconut milk. Again, this doesn’t apply to skimmed cow’s milk;
- Lower in sugar;
- Fortified with vitamins, so they actually contain more vitamin B12 and vitamin D than cow’s. Some cow’s milk is fortified with vitamin D; the ones I looked at were not fortified.
- Fortified with calcium, and have comparable amounts to dairy.
If you want to see these comparisons for specific brands (e.g. Oatly vs Alpro), then jump to the end where I include a sortable table.
Does that make plant-based milks more or less healthy?
I’m not a fan of comparing single foods on whether they’re ‘healthy or ‘unhealthy’. Someone’s nutrition is determined by the full range of foods they eat. Within that basket, the same food could be considered healthy or unhealthy.
If someone’s getting all of the protein, fibre, vitamins, and minerals they need, then a sugary treat probably isn’t ‘unhealthy’. If their diet is full of high-calorie foods without much protein or variety then having another one probably isn’t a ‘healthy’ choice.
This point also applies to the milk comparison. The average person in the UK [or pick almost any high-income country] gets more than enough calories (around two-thirds are overweight) and eats more than the national guidelines for saturated fat.¹ For this reason, switching to plant-based milk might improve their health a bit. This is because most adults get enough protein. Switching to low-protein milk might not make much of a difference.
Of course, this doesn’t apply to everyone. If you live in a lower-income country where most of your diet is made up of cereals and staples (in some countries, more than 75% of calories come from staples) and you don’t get enough protein, then swapping cow’s milk for oat milk would be a mistake. A glass of cow’s milk might be your only source of high-quality protein for the day.
Let’s then talk about protein. With the exception of soy milk, plant-based milk contain almost zero. That’s not technically true, but should be your guiding principle: if you’re drinking non-soy plant milk then you’re not getting protein from it. This is not only because the total amount of protein is less, but also because the quality is worse (more on this soon).
What about soy milk? It has almost the same amount of total protein, and is also a ‘high-quality’ source.
Is the protein in soy and other milks ‘high-quality’?
If you’re new to nutrition speak, things are going to get a little bit more technical. But hopefully I can make it understandable for you to follow along.
When it comes to protein, it’s not just the total amount that’s important. It’s also about the composition of those proteins, and how well we can digest them.
Proteins are made up of building blocks called ‘amino acids’. There are non-essential amino acids, which can be synthesised by the human body itself. And there are essential amino acids, which we can’t synthesise and we have to get from food.
There are nine essential amino acids.² To meet our protein needs, we don’t only need to get enough total protein, we also need to get enough of each essential amino acid. Even if you ate five times the recommended amount of total protein, but you didn’t meet the requirement for the amino acid ‘leucine’, you would still be protein deficient. Here, leucine would be called the ‘limiting’ amino acid because it’s the one that’s lacking.
Let’s then see how soy milk compares to cow’s milk on these nine amino acids. In the table, we have cow’s milk, plus several products of soy.³
Underneath I’ve also included the other plant-based milks. But as you can see, they tend to have small amounts.
Overall, soy milk has a similar amount of essential amino acids to cow’s milk. But they differ on which amino acids are most ‘limiting’.
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To figure out if this is ‘enough’ we need to also consider how well these amino acids can be digested in the intestine. And we need to compare it to how much of each amino acid humans actually need.
To calculate this, researchers use something called the ‘Digestible Indispensable Amino Acid Score’ (DIAAS). This score compares the amount of a particular amino acid per gram of protein in food to the amount that’s needed for an individual. Our individual needs depend on various factors, but are often done by age group; infants, small children, and adults all have different requirements.
For example, the UN FAO guidelines state that adults need 48 milligrams of lysine per gram of protein.⁴ If our food (once corrected for digestibility) had 50 milligrams then its DIAAS score would be 104%. It’s just 50 divided by 48, times 100.
We would do this calculation for each essential amino acid. And a food’s DIAAS score would be the lowest number. So if histine has a score of 150%, but lysine only 70%, then the food’s score would be 70%. You’re only as good as your worst player.
Foods are then scored as the following:
- No protein quality claim (i.e. poor) – Less than 75%
- Good protein quality – 75% to 99%
- Excellent or High protein quality – 100% or more
Let’s see how the milks compare on DIAAS scores.
All of the plant-based milks except soy are below 75%. We’ve already established that they’re poor protein sources.
A study calculated the DIAAS scores for cow’s and soy milk in three populations: infants under 6 months; young children up to 3 years; and older children, adolescents and adults.
For infants: Cow’s and soy milk were both below 75%. Neither are appropriate; babies need breast milk or infant formula for many reasons beyond protein.
For young children: Cow’s milk scored ‘excellent’ with a rating of 123%. Soy milk scored 92%, which makes it a ‘good’ quality source.
For adults: Both were ‘excellent’ protein sources. Cow’s milk scored 145%, and soy milk scored 108%.
To sum up: soy and cow’s milk are both complete protein sources for older children and adults. Soy is good, but not excellent, protein source for younger children (over one year old). You’d want to pair it with something else to bump up the score for the meal. Neither cow’s or soy milk should be given to infants.
Plant-based milks are fine for some people, but not appropriate for others
There are populations where this swap would be bad for nutrition. In many low-income countries, many people don’t get enough high-quality protein. Making that switch without other changes in diet would be a bad choice.
This is also true for infants, as I discussed earlier. And some other demographics, such as older people, where protein requirements are higher. Of course, someone can change their diet in other ways to make sure they’re still meeting their protein needs but this would need to be done with care.
But for many people, plant-based milks are a good replacement. They’re an obvious win for the lactose intolerant. For adults in many countries, where protein deficiency is often not a concern, there are few nutritional downsides. My advice is to look for ones that are fortified with calcium and vitamin B12, which are often lacking in more plant-based diets.⁵
Nutritional breakdown by plant-based brand
In the table below I’ve provided more comparisons between specific plant-based products. This includes different brands of milks (e.g. Oatly, Alpro, Koko) but also different variations of the milks themselves. Most have a sweetened and ‘no sugar’ version.
