Swapping regular milk for oat milk or choosing plant-based yogurt instead of dairy might seem like a simple change. But are you getting the same nutrients when you make the switch?
Not always, according to a new study published in The Lancet Planetary Health. Researchers found that replacing even some dairy products with plant-based alternatives could reduce intake of important nutrients, particularly iodine, which supports thyroid function and healthy brain development.
The findings don't mean plant-based alternatives are unhealthy. They do suggest that what's in the carton or container matters, especially for people gradually shifting toward more plant-based foods.
Researchers from the University of Surrey and Queen's University Belfast analyzed dietary information from more than 3,500 people in the United Kingdom. They then estimated what would happen if people replaced varying amounts of dairy milk, yogurt and cheese with plant-based alternatives sold in British supermarkets.
The biggest concern was iodine, although researchers also found potential declines in calcium, vitamin B12 and riboflavin, or vitamin B2.
When they modeled replacing 35% of dairy products with plant-based alternatives, the proportion of teenage girls getting too little iodine increased from 54% to 65%. Among women ages 19 to 49, it rose from 32% to 42%.
Those numbers reflect estimates of inadequate nutrient intake, not actual diagnosed deficiencies. The study used computer modeling rather than following people who changed their diets.
"People may also be unaware of the importance of iodine, which is needed to make thyroid hormones to regulate our metabolism, support healthy growth and brain development," said Sarah Bath, an associate professor at the University of Surrey and lead author of the study.
The U.K. is particularly vulnerable to iodine shortfalls because dairy is a major source of the nutrient and iodized salt isn't widely used. In the United States, people also can get iodine from iodized table salt, seafood and eggs, so the British estimates don't necessarily reflect what would happen in American diets.
Still, the broader finding is relevant to shoppers on either side of the Atlantic. Plant-based alternatives may look and function like dairy products, but they don't always provide the same nutrition.
As previously reported, plant-based milks vary considerably in their protein, vitamin and mineral content. Some fortified soy milks offer nutrition comparable to dairy milk, while other products provide much less of certain nutrients.
The encouraging news is that the researchers also found a potential solution. When they modeled adding iodine, calcium, vitamin B12 and riboflavin to plant-based alternatives, the projected nutrient shortfalls were largely prevented. Adding iodine to bread could offer additional benefits, particularly for people already at risk of getting too little.
The findings reinforce the importance of fortification, or adding nutrients to foods, as more people choose plant-based options.
That's particularly relevant for children and teenagers, whose nutritional needs are changing as they grow. Previous research on plant-based diets in children has similarly highlighted the importance of getting enough essential nutrients.
The study does have limitations. It relied on British dietary surveys from 2016-2019 and plant-based product information collected in 2020. Products may have changed since then, and researchers didn't measure actual health outcomes.
For consumers, the research offers a useful reminder that foods serving the same purpose in a meal aren't necessarily nutritionally interchangeable. Checking labels for added nutrients, including calcium and vitamin B12, can help when choosing plant-based alternatives. Iodine deserves attention, too, although it isn't always listed on U.S. nutrition labels.
The study was supported by the U.K.'s Biotechnology and Biological Sciences Research Council through its FoodBioSystems program. Two researchers reported honoraria for educational presentations from dairy industry organizations, with one also receiving an honorarium from Oatly UK, a plant-based beverage company.