Replacing even a fifth of the milk, cheese and yogurt in a national diet with the plant-based alternatives currently on store shelves lowers intake of iodine, calcium, riboflavin and vitamin B12, with iodine falling furthest. That is the central result of a modeling study by researchers at the University of Surrey and Queen's University Belfast, published in the September 2026 issue of The Lancet Planetary Health. The paper also models the fix: mandatory fortification of plant-based dairy alternatives, iodized salt in bread, or both.

What the study did

This was not a feeding trial and nobody's diet changed. The team took the UK National Diet and Nutrition Survey, a government record of what people actually eat, and replaced dairy products gram for gram with commercially available plant-based milks, yogurts and cheeses at 20, 35, 50 and 100 percent, levels chosen to match the UK's Net Zero targets and the EAT-Lancet diet. Usual nutrient intakes were then estimated with the National Cancer Institute method and compared with requirements under two conditions: the fortification that products carry today, and a hypothetical rule requiring every alternative to be fortified. Funding came from the Biotechnology and Biological Sciences Research Council's FoodBioSystems program.

What it found

Under current fortification, swapping 35 percent of dairy cut mean daily iodine intake by 9 to 21 percent, and swapping half cut it by 13 to 28 percent across most groups. The groups that lost most were young children, adolescents and adult women, who already sit closest to the line on iodine. At full replacement, the share of adolescents with inadequate iodine intake rose to 72 percent of boys and 80 percent of girls. Calcium, riboflavin and B12 intakes also fell at 35 and 50 percent replacement, but the share of people below requirements only rose at the higher replacement levels.

Requiring fortification changed the picture. When every alternative was modeled as fortified with iodine, calcium, riboflavin and B12, mean intakes held steady at every replacement level, though iodine inadequacy stayed high where it was already high: 56 to 59 percent of girls aged 14 to 18 and 32 to 37 percent of women aged 19 to 49 remained below the estimated average requirement. Adding iodized salt to bread helped more at low replacement levels, cutting inadequacy among teenage girls from 54 percent to 37 percent with no dairy replaced at all. Combining both measures worked best, keeping iodine adequacy at or above baseline in every age group even when dairy was fully replaced. No scenario pushed any group over the upper intake limit.

What it does not show

The paper is a model of British diets and British products. It cannot say how many people would actually develop a deficiency, because it estimates intake against requirements rather than measuring thyroid function or blood levels, and it assumes people replace dairy with an alternative rather than dropping the category. The US market, with its own fortification habits and its own iodine sources, was not studied.

Some context does carry across the Atlantic. The National Institutes of Health Office of Dietary Supplements lists dairy as a meaningful iodine source in the American diet, with nonfat milk averaging about 84 micrograms per cup against an adult recommended dietary allowance of 150 micrograms, and notes that soy and almond beverages contain relatively small amounts unless fortified. It also reports that the median urinary iodine concentration among US women of reproductive age in the 2007 to 2014 survey years was 119 micrograms per liter, above the 100 microgram threshold for a population but not by a wide margin.

Where dairy sits in US guidance

The Dietary Guidelines for Americans, 2025-2030, issued jointly by the Departments of Health and Human Services and Agriculture, set a goal of three servings of dairy per day as part of a 2,000-calorie pattern, adjusted for individual calorie needs, and describe dairy as a source of protein, fats, vitamins and minerals. The guidelines advise full-fat dairy with no added sugars when dairy is consumed. The new UK model does not argue against plant-based alternatives; it argues that the nutrients dairy carried need to arrive some other way, and it quantifies how far voluntary fortification currently falls short of doing that.

For a reader who has already switched, the practical question is on the label: whether the carton lists iodine, calcium and B12 among its added nutrients, and in what amounts. For anyone with a thyroid condition or who is pregnant, the iodine question belongs in the next clinic visit.

This article reports research and expert guidance. It is not medical advice. Talk to your clinician before changing medication, treatment or a medical diet.

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