Plant-based milk sales have surged globally, with the category now worth over $20 billion annually. Oat, almond, soy, coconut, rice. The options multiply every year, and so does the marketing around them. What doesn't always multiply is the nutritional content inside the carton.
A study from the University of Surrey drew a clear line between what consumers assume they're getting and what they're actually getting. The finding: swapping dairy milk for unfortified plant-based alternatives creates measurable nutrient gaps. Not theoretical ones. Real deficiencies that accumulate over time, particularly for people with elevated nutritional demands.
If you've made the switch, or you're thinking about it, here's what you need to understand before your next grocery run.
What the Research Actually Found
The University of Surrey study examined the nutritional profiles of popular plant milks against cow's milk, focusing on what happens to micronutrient intake when dairy is displaced from the diet entirely. The results weren't a condemnation of plant milks. They were a warning about a specific subset: unfortified versions.
The nutrients most at risk when unfortified plant milks replace dairy are calcium, iodine, vitamin B12, and vitamin D. These aren't fringe micronutrients. They're foundational to bone density, thyroid function, neurological health, and immune regulation. Dairy is one of the primary delivery vehicles for all four in the typical Western diet.
When you remove dairy without replacing those nutrients through fortified alternatives or other dietary sources, the gap doesn't fix itself. It widens quietly, over weeks and months, until symptoms emerge or a blood panel catches up with you.
The Fortified vs. Unfortified Distinction Most People Miss
This is the variable that most consumers overlook entirely. Not all plant milks are created equal, and the word "plant-based" on a label tells you nothing about the nutrient content inside. A barista oat milk and a calcium-fortified oat milk can sit on the same shelf, look nearly identical, and differ dramatically in nutritional value.
Fortified plant milks are specifically engineered to approximate the micronutrient profile of dairy. They typically contain added calcium (often around 120mg per 100ml, comparable to cow's milk), vitamin D2 or D3, and sometimes B12 and iodine. Unfortified versions contain none of these additions. What you're drinking is essentially the base ingredient, water, and perhaps a stabilizer.
The challenge is that "natural" or "clean label" marketing often steers consumers toward unfortified options without making the nutritional trade-off explicit. A product that positions itself as free from additives may genuinely have fewer ingredients. It may also have a fraction of the nutritional value you're counting on.
Reading the nutrition panel isn't optional. It's the only way to know what you're actually buying.
Why Athletes and Active People Are at Greater Risk
If you train regularly, your baseline requirements for several of these nutrients are already elevated compared to a sedentary person. That means the gap created by unfortified plant milks hits harder, and the consequences compound faster.
Calcium is the clearest example. Athletes place higher mechanical stress on bone tissue, and adequate calcium intake is essential to maintaining bone mineral density over time. Studies consistently show that athletes, particularly those in endurance or high-impact sports, are more susceptible to stress fractures when calcium intake is chronically low. If you've replaced dairy with an unfortified almond milk that contains roughly 20mg of calcium per 100ml (versus dairy's 120mg), that shortfall adds up across every meal and snack where milk appears.
Vitamin D compounds the problem. It's required for calcium absorption. Without sufficient vitamin D, even adequate calcium intake becomes less effective. Deficiency is already widespread in northern latitudes regardless of diet, and athletes training indoors face additional risk. The University of Surrey research flagged vitamin D as one of the nutrients most likely to fall below recommended intakes when unfortified plant milks replace dairy.
Iodine is the often-forgotten one. Dairy is a significant source of dietary iodine in the UK, US, and Australia, largely because iodine-containing disinfectants are used in dairy farming. Plant milks contain almost no iodine unless specifically fortified. Iodine is critical for thyroid hormone production, which directly regulates metabolism and energy availability. For athletes, suboptimal thyroid function affects everything from training adaptation to recovery capacity.
Vitamin B12 matters for the same reason. It's involved in red blood cell production and neurological function. Inadequate B12 impairs oxygen-carrying capacity, which is not a position any endurance athlete wants to be in. The topic of micronutrient blind spots in female athletes is covered in depth in Sports Nutrition for Women: The Gaps Nobody Talks About, and B12 sits squarely within that conversation.
Iron isn't part of the University of Surrey findings specifically, but it belongs in this discussion. Athletes who also reduce red meat intake alongside dairy face a compounding risk. If that describes you, The Lifter's Guide to Iron: Why Women Need to Pay Attention is worth reading alongside this piece.
How to Read the Label and Know What You're Getting
The nutrition panel is your first stop. Look for the per-100ml column, not per serving, since serving sizes vary between brands and are often larger than what you'd actually pour.
Here's what to check for in a plant milk you're using as a dairy replacement:
- Calcium: Look for at least 120mg per 100ml. This is roughly equivalent to cow's milk. If the label shows 20-30mg, the product isn't a nutritional substitute for dairy on this metric.
- Vitamin D: Any amount is better than none. Some brands add 1-2 micrograms per 100ml. Check whether it's D2 or D3. D3 is more bioavailable.
- Vitamin B12: Usually listed in micrograms. It's particularly important if dairy was your primary B12 source and you're not eating meat.
- Iodine: Often absent from plant milks, even fortified ones. This is a gap you may need to address separately, through iodized salt, seaweed-based supplements, or multivitamins that include iodine.
Beyond the nutrition panel, check the ingredient list. If a product markets itself as "natural" or "minimal ingredient," it's worth assuming it's unfortified unless the nutrition panel confirms otherwise. The marketing language and the nutritional reality are often running on completely different tracks.
When a Targeted Supplement Actually Fills the Gap
Whole food sources should always be the first line of strategy. Calcium from leafy greens, tofu, and fortified foods. B12 from eggs, meat, or fortified cereals. Vitamin D from safe sun exposure and fatty fish. Iodine from seafood or iodized salt. Building dietary variety around these sources is more reliable than relying on any single product.
But there are situations where supplementation is the practical answer, not a workaround. If you're vegan, your B12 intake from food alone is almost certainly insufficient. Supplementing directly is the standard recommendation from most dietary health bodies. If you live at a northern latitude and train primarily indoors through winter, vitamin D supplementation is similarly well-supported by evidence. If your plant milk of choice doesn't deliver meaningful iodine, and you don't eat seafood regularly, an iodine-containing supplement closes that gap efficiently.
The challenge with supplements is that the category is poorly regulated and trust in it has eroded for good reason. Supplement Trust Is Broken. Here's How to Navigate It is a useful starting point for evaluating what's actually worth buying and what's label noise. Third-party certification (NSF, Informed Sport, USP) matters if you're an athlete subject to testing, and it's a reasonable quality signal for everyone else.
One principle worth holding: supplements work best when they're targeted at a confirmed or plausible gap, not taken as a nutritional insurance policy for a diet that hasn't been properly assessed. If you've made significant dietary changes, including replacing dairy with plant milks, getting a blood panel done is a reasonable baseline move. It costs relatively little and gives you actual data to work with rather than assumptions.
This kind of precision-first thinking applies across the broader nutrition landscape. The same logic that underpins careful supplement use shows up in the conversation around GLP-1 Users: Why Food Quality Beats Calorie Counting. The form of what you eat matters as much as the quantity, and micronutrient density is where many modern diets quietly fall short.
The Bottom Line on Plant Milk and Nutrition
Plant milks aren't nutritionally inferior by definition. Fortified versions can match dairy's key nutrient contributions reasonably well. The issue is that a large portion of what's on shelves is unfortified, and marketing language frequently obscures that fact.
If you've switched to plant milk, your job is straightforward: confirm that your chosen product is fortified for calcium, vitamin D, and ideally B12. Build iodine into your diet through other sources. If you're an athlete, treat these nutrients with the same seriousness you'd apply to protein or carbohydrate timing, because the downstream effects on bone, thyroid, and energy metabolism are real and measurable.
The plant-milk category will keep growing. The gap between what's marketed and what's inside the carton won't close on its own. You have to close it yourself.