Of these three trace elements, only one is a genuine problem on a Swiss vegetarian diet: iodine. The Federal Food Safety and Veterinary Office (FSVO) states that a balanced ovo-lacto-vegetarian diet supplies a healthy adult with enough iron, zinc, calcium and B vitamins. Zinc deserves attention to preparation methods rather than anxiety. Selenium is easy to cover, provided you know that two Brazil nuts already exceed the reference intake. Iodine is the one that collapses as soon as you drop fish and swap cow’s milk for an unfortified plant drink: in a systematic review published in Nutrients in 2021, 92 % of the vegans analysed had a urinary iodine concentration below the sufficiency threshold, against 51 % of meat-eaters.

This article gives the actual reference intakes, measured food values, what soaking really changes, and the two situations where more becomes worse: Brazil nuts and seaweed.

What the authorities say, and what they do not

Swiss official guidance on vegetarian eating is more nuanced than the alarms you usually read. The FSVO separates four patterns and assigns them different risks:

• Ovo-lacto-vegetarian (eggs and dairy included): iron, zinc, calcium and B vitamins adequate in a healthy adult.
• Lacto-vegetarian (dairy, no eggs): requirements can be met with several dairy servings a day, only vitamin B12 may fall below the recommendation.
• Ovo-vegetarian (eggs, no dairy): the profile of critical nutrients resembles a vegan diet.
• Vegan: without careful planning, risk of deficiency in vitamin B12, iodine and zinc.

That classification changes how you should read the rest. If you eat cheese and yoghurt, zinc is probably not your issue. If you have cut out dairy, iodine becomes a serious question, because milk is one of the few reliable sources in a Western diet.

These three elements share another feature: the window between too little and too much is narrow. That is especially true for iodine and selenium, where the safe upper limit is reachable with ordinary foods and no supplement at all.

Zinc

How much, and by whose reference

The numbers differ between institutions, which explains the contradictory figures in circulation.

Reference	Adult man	Adult woman
Recommended Dietary Allowance (Institute of Medicine, used by the NIH)	11 mg	8 mg
UK reference (NHS)	9.5 mg	7 mg
Swiss labelling reference value (Food Information Ordinance, annex 10)	10 mg	10 mg

Pregnancy adds 3 mg a day and lactation 4 mg, according to the NIH. The tolerable upper intake level for adults is 40 mg a day from all sources combined.

Zinc is required for the catalytic activity of hundreds of enzymes, for protein and DNA synthesis, wound healing and cell division. It is also involved in the sense of taste, which is why altered taste appears among the signs discussed when status is low.

What the research on vegetarians actually shows

A meta-analysis published in the Journal of the Science of Food and Agriculture in 2013 pooled 34 studies, of which 26 directly compared vegetarian and non-vegetarian groups across 48 comparisons. Zinc intakes were lower by 0.88 ± 0.15 mg a day in vegetarians (p < 0.001) and serum zinc by 0.93 ± 0.27 µmol/l (p = 0.001). The gap was wider in women, in developing countries and in vegans.

The systematic review published in Nutrients in 2021 goes further. Adjusting for the reduced bioavailability of plant zinc, it uses an estimated average requirement of 10.3 mg a day for women and 14.3 mg for men. Mean intakes in vegetarian and vegan groups fell below that threshold for men. The prevalence of zinc deficiency was 14 % in vegetarians and 13 % in meat-eaters, but 30 % in vegans.

In practical terms: the gap is real, it is modest for ovo-lacto-vegetarians, and it becomes meaningful once dairy and eggs go too.

Sources and their measured content

The values below come from the USDA FoodData Central database, as reported by the NIH.

Food	Portion	Zinc
Pumpkin seeds, roasted	28 g	2.2 mg
Porridge oats, cooked in water	1 cup (about 230 g)	2.3 mg
Lentils, boiled	about 100 g	1.3 mg
Cheddar-style cheese	43 g	1.5 mg
Greek yoghurt, plain	170 g	1.0 mg
Milk	2 dl	1.0 mg
Peanuts, dry roasted	28 g	0.8 mg
Brown rice, cooked	about 100 g	0.7 mg
Kidney beans, canned	about 90 g	0.6 mg
Wholemeal bread	1 slice	0.6 mg
Egg	1 large	0.6 mg
Broccoli, cooked	about 80 g	0.4 mg

Two things follow. Fruit and vegetables contribute almost nothing: reaching 8 to 11 mg on salads does not work. And dairy carries real weight in a daily total, which is consistent with the FSVO position.

Phytates, and what soaking really changes

Phytates are the storage form of phosphorus in seeds. They bind zinc in the gut and form an insoluble complex that inhibits absorption. That is the central mechanism, documented by the NIH, and it applies to exactly the foods a vegetarian diet rests on: pulses, whole grains, nuts and seeds.

The NIH explicitly advise people on vegetarian and vegan diets to soak beans, grains and seeds in water for several hours before cooking, to reduce that binding. Soaking and sprouting pulses and sourdough fermentation work in the same direction.

One caveat matters. The size of that gain is not reliably quantified for a given meal. In vitro bioaccessibility studies give modest and inconsistent figures. A 2026 study on black beans grown in Mozambique measured zinc bioaccessibility of 6.52 % after ordinary cooking, 8.41 % under pressure cooking, 7.58 % after 24 hours of germination and 10.08 % after 48 hours. Every method improved on the untreated control, but the differences between methods were not statistically significant, except for pressure cooking with iron. The practice is sensible and costs nothing; it is not dramatic.

Vitamin C helps iron absorption, not zinc absorption

You will often read that zinc-rich foods should be paired with vitamin C to improve absorption. That rule holds for non-haem iron, not for zinc. The factors that govern zinc absorption are the amount of zinc in the meal, its phytate content, and high-dose iron or copper intake. A glass of orange juice alongside lentils is pleasant; it does not change your zinc status.

Safety and interactions

High zinc intake reduces copper absorption, which can lead to anaemia and weakened bones. The NHS advises against exceeding 25 mg a day from supplements without medical advice, and the NIH upper limit is 40 mg from all sources. Zinc also interacts with quinolone and tetracycline antibiotics: taking the antibiotic at least 2 hours before or 4 to 6 hours after the supplement limits the interaction. It also reduces absorption of penicillamine.

If supplements are on your mind, our piece on zinc supplements and vegetarianism covers the situations where they are justified.

Selenium

Requirements and limits

The recommended intake is 55 µg a day for adults, 60 µg in pregnancy and 70 µg during lactation. The NHS uses 75 µg for men and 60 µg for women. The Swiss labelling reference value is 55 µg.

The Institute of Medicine upper limit is 400 µg a day. In 2023 the European Food Safety Authority panel revised that downwards to 255 µg a day for all adults, including during pregnancy and lactation, based on systematic reviews of alopecia.

The characteristic sign of chronic excess, selenosis, is hair loss and brittle or shedding nails. Other reported effects include skin rash, nausea, diarrhoea, fatigue and irritability.

The Brazil nut question, with numbers

This is where most vegetarian cooking articles point the wrong way.

A 28 g portion of Brazil nuts, six to eight nuts, provides 544 µg of selenium according to the NIH, who give a range of 68 to 91 µg per nut. In other words:

• One nut already covers the 55 µg reference intake comfortably.
• Two nuts give 136 to 182 µg, two to three times the recommendation.
• A handful of six nuts gives roughly 400 to 550 µg, above the European upper limit of 255 µg.

A randomised controlled trial published in the American Journal of Clinical Nutrition in 2008 followed 59 New Zealand adults for 12 weeks. Two Brazil nuts a day, supplying an average of 53 µg of selenium with an actual range of 20 to 84 µg depending on the nuts, raised plasma selenium by 64.2 %, against 61.0 % with 100 µg of selenomethionine and 7.6 % on placebo. Whole-blood glutathione peroxidase activity rose more in the Brazil nut group than in either other group.

Two lessons. Brazil nuts genuinely work, better than a supplement at an equivalent dose. And the variability between nuts is such that you cannot dose them precisely: the measured 20 to 84 µg spread per nut is enough to explain why the sensible rule is one to two nuts a day at most, not a handful.

Other sources, and the soil factor

The selenium content of plant foods depends on the soil: the amount and chemical form of selenium, soil pH, organic matter. A grain grown on poor soil holds little, the same grain grown elsewhere holds far more. That is why composition tables are approximate for this element.

Indicative NIH values, Brazil nuts aside:

Food	Portion	Selenium
Pasta, cooked	1 cup	33 µg
Cottage cheese	1 cup	20 µg
Egg, hard-boiled	1 large	15 µg
Porridge oats, cooked	1 cup	13 µg
Portobello mushrooms, grilled	about 80 g	13 µg
Brown rice, cooked	1 cup	12 µg
Wholemeal bread	1 slice	8 µg
Yoghurt, plain low fat	1 cup	8 µg
Lentils, boiled	1 cup	6 µg
Milk	2 dl	6 µg

An ordinary meal of wholemeal pasta, mushrooms and a yoghurt already approaches 55 µg. Selenium is rarely the weak point of a varied ovo-lacto-vegetarian diet in western Europe.

A safety note on supplements: in 2008, in the United States, 201 people had severe adverse reactions after taking a liquid dietary supplement that contained 200 times the labelled amount of selenium. The dose printed on a package is not a guarantee.

Iodine, the real weak point

Requirements, and the gap between reference bodies

The recommended intake is 150 µg a day for adults according to the Institute of Medicine and the World Health Organization. The NHS uses 140 µg. The Swiss labelling reference value is 150 µg. In pregnancy the WHO recommends 250 µg a day, the Institute of Medicine 220 µg, and 290 µg during lactation.

The upper limit is 1100 µg a day for adults according to the Institute of Medicine. The European Food Safety Authority proposes a lower figure of 600 µg. The American Thyroid Association advises against supplement intakes above 500 µg a day in children and adults alike, including during pregnancy and lactation.

Iodine does one job, and it is a central one: thyroid hormone synthesis. More than 90 % of dietary iodine is excreted in urine, which is why urinary iodine serves as a population-level status marker.

Why vegetarians are affected

In a Western diet, the reliable sources are fish, seafood, eggs, milk and dairy, plus iodised salt. Plant foods contain little, seaweed excepted. Milk content depends on cattle feed and on-farm hygiene practices, which makes it variable but significant, particularly in children.

Plant drinks used in place of milk, whether soya or oat, contain very little iodine unless fortified. The NHS says this explicitly and asks readers to check the label. On the NIH table, a cup of soy beverage supplies 3 µg of iodine, against 84 µg for a cup of skimmed milk.

The numbers back the mechanism. The 2021 Nutrients review reports mean intakes of 111 µg a day in vegans, 146 µg in vegetarians and 170 µg in meat-eaters. More striking, the prevalence of urinary iodine below 100 µg/l reached 92 % in vegans, against 37 % in vegetarians and 51 % in meat-eaters.

In Switzerland the general picture remains sound. A cross-sectional study of 6341 adults aged 35 to 75 in the city of Lausanne, published in 2025, measured a median urinary iodine concentration of 131 µg/l, 123 µg/l in women and 138 µg/l in men. Overall 70.5 % of participants had adequate status, 23.0 % mild deficiency, 6.0 % moderate and 0.5 % severe. Adequate status at population level says nothing about your own plate, but it does show the Swiss arrangement works for most people.

Swiss iodised salt, in usable numbers

The federal ordinance on adding vitamins, minerals and certain other substances to foodstuffs sets the rule in article 5: table salt to which iodide or iodate has been added must contain 20 to 40 mg per kilogram, calculated as iodine.

The arithmetic is then simple:

• 1 g of Swiss iodised salt supplies 20 to 40 µg of iodine.
• 5 g of salt a day, the WHO ceiling for sodium, supplies 100 to 200 µg, which brackets the 150 µg recommendation.
• Non-iodised sea salt, fleur de sel and Himalayan salt supply nothing. On the NIH table, non-iodised sea salt is 0 µg.

This is the cheapest and most effective single measure, and it does not require eating saltier food: it requires replacing the salt you already use. Check the wording on the packet, which is mandatory in Switzerland when salt has been fortified.

Our dedicated pieces on balancing iodine with seaweed and iodised salt and on avoiding iodine deficiency without fish go deeper into day-to-day practice.

Seaweed: the strongest source and the riskiest

Seaweed is the only genuinely iodine-rich plant source. It is also the only common food capable of causing an excess.

The scale of the variability is the decisive point. A study published in Thyroid in 2004, cited by the NIH, measured concentrations ranging from 16 µg to 2984 µg per gram in commercially available seaweeds sold whole or in sheets. A factor of 186 between two products on the same shelf. Two tablespoons of dried nori, about 5 g, supply roughly 116 µg according to the same source, but that figure is an average, not a guarantee.

The review published in Frontiers in Endocrinology in 2025 on iodine in vegetarian and vegan diets is blunt: iodine availability from seaweed is highly variable and can reach up to a hundred times the reference intake. Its authors recommend iodised salt and, where needed, a titrated supplement of 150 µg of potassium iodide, and discourage uncontrolled seaweed consumption, especially in children, where heavy metal contamination adds a second concern.

A case published in Cureus in 2024 shows what “uncontrolled” means. A previously healthy 43-year-old man had been eating tororo kombu at every meal for six months, originally for its supposed effect on constipation. His iodine intake was estimated at 40 to 80 mg a day, against the 0.13 to 0.15 mg recommended in Japan, several hundred times the reference intake. His thyroid-stimulating hormone was 36.3 µIU/ml and free thyroxine below 0.40 ng/ml, with negative thyroid antibodies. Hypothyroidism from seaweed overconsumption was only diagnosed after a detailed dietary history was taken a second time. Thyroid function normalised within about a month on hormone replacement.

The case is extreme and does not describe what happens with a sheet of nori on a rice bowl. It does explain why the sensible rule is: seaweed as an occasional, flavourful ingredient, not as a daily iodine strategy. Our articles on edible seaweeds and on cooking with dulse, wakame, nori and kombu start from the same premise.

Two technical points are worth knowing. Kombu is by far the most concentrated seaweed on the shelf, which makes it the one to treat with most caution and, awkwardly, the one stock recipes use most. Soaking kombu and then removing it from the stock transfers part of the iodine into the water; that is a real effect, but it lets you soften a peak, not calculate a dose.

Pregnancy, breastfeeding, children

These are the situations with the least margin for error in either direction. Deficiency during pregnancy is associated with a raised risk of growth restriction and impaired fetal brain development, and requirements rise because of increased maternal hormone synthesis, greater urinary loss and transfer to the fetus.

The Frontiers in Endocrinology review recommends that vegetarian or vegan women start a low-dose supplement ideally three months before conception, use iodised salt, and take 150 to 225 µg of potassium iodide a day during pregnancy and breastfeeding. It also reports a UK case of transient hypothyroidism with goitre in the child of a vegan mother with severely restricted iodine intake.

In children, seaweed consumption is generally discouraged because of the risk of iodine overload and heavy metal contamination. Unfortified plant drinks pose the same problem as in adults, more sharply, since milk is a major iodine source in children’s diets.

None of this is settled by an article. Supplementation in these situations belongs to a doctor or a registered dietitian, which is also what the FSVO recommends.

Goitrogens, without the drama

Soya, cassava and cruciferous vegetables such as cabbage, broccoli and cauliflower contain substances that interfere with iodine uptake by the thyroid. Iron and vitamin A deficiency are also goitrogenic.

The NIH are clear about the real scope: this concerns mainly people living in areas prone to iodine deficiency. For most people with adequate iodine intake and a varied diet, eating reasonable amounts of goitrogen-containing foods is not a concern. Giving up broccoli will not improve your thyroid; using iodised salt will.

A day that covers all three

The targets are 8 to 11 mg of zinc, 55 µg of selenium and 150 µg of iodine, within the Swiss food pyramid framework: 5 portions of fruit and vegetables of which 3 are vegetables, 3 portions of starchy foods, 2 to 3 dairy portions, 1 protein-rich portion and 15 to 30 g of nuts or seeds.

Breakfast: 60 g of oats cooked in water with 2 dl of milk or a fortified plant drink, 20 g of pumpkin seeds, a piece of fruit. Roughly 3.5 mg of zinc, a solid share of the day’s selenium, and iodine if you use milk or a fortified drink.

Lunch: 60 g of dry lentils cooked, brown rice, seasonal vegetables, seasoned with iodised salt. Around 2 mg of zinc, 15 to 20 µg of selenium, and 20 to 60 µg of iodine depending on how much salt goes in during cooking and at the table.

Snack: one Brazil nut. On its own it supplies 68 to 91 µg of selenium, which settles the question for the day.

Dinner: wholemeal pasta bake with mushrooms, 30 g of hard cheese, salad. About 2.5 mg of zinc, another 30 µg of selenium, plus the iodine in the cheese.

This plan contains no seaweed and no supplement. That is deliberate: it is the most robust configuration for an ovo-lacto-vegetarian. Remove the dairy and the iodine line collapses, and has to be rebuilt with iodised salt, fortified plant drinks and, often, a titrated supplement.

Three weighed recipes

Quinoa bowl with pumpkin seeds and roast chickpeas (serves 2)

• 150 g raw quinoa, rinsed
• 240 g cooked chickpeas, drained
• 40 g pumpkin seeds
• 200 g seasonal vegetables, diced
• 2 tablespoons rapeseed oil
• 4 g iodised salt, cumin, paprika, juice of half a lemon

Soak the chickpeas overnight if starting from dry, then cook them. Roast them for 25 minutes at 200 °C with one tablespoon of oil and the spices. Cook the quinoa for 12 to 15 minutes. Pan-fry the vegetables. Assemble, season with the iodised salt, add the raw pumpkin seeds at the last moment along with the lemon juice.

Approximate values per serving: about 3.5 mg of zinc, 15 to 25 µg of selenium depending on where the quinoa was grown, 40 to 80 µg of iodine depending on how the salt is split.

Wholemeal pasta bake with mushrooms (serves 2)

• 180 g raw wholemeal pasta
• 250 g button or portobello mushrooms, sliced
• 2 dl milk or fortified plant drink
• 60 g hard cheese, grated
• 1 tablespoon rapeseed oil, garlic, thyme
• 3 g iodised salt

Cook the pasta one minute short of the stated time. Fry the mushrooms over high heat until all their water has evaporated, then add garlic and thyme. Combine pasta, mushrooms and milk, season, cover with cheese and bake for 20 minutes at 200 °C.

This dish stacks three selenium sources that do not depend on any single soil: the pasta, the mushrooms and the cheese. Count roughly 30 to 40 µg of selenium and 2.5 mg of zinc per serving, plus the iodine from cheese and salt.

Miso soup with vegetables and tofu, without an iodine spike (serves 2)

• 8 dl water
• One 5 cm piece of kombu, optional
• 200 g firm tofu, diced
• 150 g seasonal vegetables, finely sliced
• 2 tablespoons miso paste
• Spring onions, sesame oil

If you use kombu, soak it for 20 minutes in cold water, heat without boiling, then remove it before the boil. Add the vegetables and tofu and simmer for 5 minutes. Turn off the heat, slacken the miso in a ladle of hot stock and stir it in off the heat.

The kombu is optional and deliberately removed early. Miso brings salt of its own: if you use it, cut or drop any other salt in the dish. This soup is not your iodine source for the day; it is a seasonal dish.

Six common mistakes

1. Relying on fruit and vegetables for zinc. They contain very little. The levers are seeds, pulses, whole grains and, if you eat them, dairy products.
2. Pairing zinc with vitamin C to improve absorption. That rule applies to non-haem iron. It has no basis for zinc.
3. Eating a handful of Brazil nuts. Six nuts exceed the European upper limit of 255 µg a day. One or two are enough, and the spread between nuts is roughly fourfold.
4. Using sea salt or fleur de sel thinking it is an upgrade. These salts supply no iodine. The public health benefit comes from fortification, not from the origin of the salt.
5. Treating seaweed as a daily supplement. Content varies by a factor of 186 between products, and chronic excess disturbs the thyroid.
6. Swapping milk for a plant drink without reading the label. An unfortified soy drink supplies about 3 µg of iodine per cup, against 84 µg for milk.

Scope and precautions

Individual testing remains essential. Serum zinc is an imperfect marker, sensitive to inflammation and fasting, and urinary iodine from a single sample reflects an individual’s status poorly even though it is reliable at population level. A one-off measurement can therefore mislead in either direction.

No personalised dose can be inferred from these reference points. The upper limits quoted are population thresholds, not targets. If you take thyroid medication, an antithyroid drug, an ACE inhibitor or a potassium-sparing diuretic, supplemental iodine can interact: the NIH flag an additive effect with antithyroid drugs and a raised risk of hyperkalaemia with the other two classes. That conversation belongs with your doctor.

Vitamin B12, the number one critical nutrient on a meat-free diet, follows a different logic. It has its own article, as does the overall structure of protein intake.

Frequently asked questions

Is an ovo-lacto-vegetarian diet enough for all three? For zinc and selenium, the FSVO considers a balanced ovo-lacto-vegetarian diet sufficient for a healthy adult. For iodine, the answer depends entirely on your salt: with iodised salt and dairy, yes; without, intake becomes uncertain.

Do vegetarians need a zinc supplement? Not as a rule. The average gap measured in the literature is under 1 mg a day in vegetarians, and deficiency prevalence there is comparable to meat-eaters. Vegans are a different case, with 30 % deficiency in the 2021 review.

Does iodised salt lose its iodine during cooking? Some iodine can be lost at high temperature and in the presence of moisture, which is reason enough to salt at the end of cooking or at the table rather than only at the start. It is not a reason to abandon iodised salt.

Is nutritional yeast a source of these three elements? It supplies B vitamins and a modest amount of zinc. It is not a notable source of selenium or iodine, unless fortification is declared on the packet. See our article on nutritional yeast.

Do broccoli and cabbage harm the thyroid? Not in a varied diet with adequate iodine intake. The issue concerns mainly populations living in iodine-deficient areas.

How much seaweed is reasonable? There is no universal safe dose, precisely because content varies by a factor of 186 between products. In practice: occasional use, small portions, nori sheets in preference to concentrated kombu, and particular caution in pregnancy and in children.

How do I know whether my salt is iodised in Switzerland? The statement is mandatory on the packaging. If it is iodised, it contains 20 to 40 mg of iodine per kilogram under federal ordinance, that is 20 to 40 µg per gram.

Sources

• NIH Office of Dietary Supplements, health professional fact sheets on zinc, selenium and iodine
• NHS, Vitamins and minerals: others and Iodine
• FSVO, Swiss nutrition recommendations for adults and vegetarian and vegan diets
• Ordinance on the addition of vitamins, minerals and certain other substances to foodstuffs, article 5
• Ordinance on food information, annex 10
• Croce et al., Frontiers in Endocrinology, 2025, Modern challenges of iodine nutrition: vegan and vegetarian diets
• Neufingerl and Eilander, Nutrients, 2021, Nutrient intake and status in adults consuming plant-based diets compared to meat-eaters
• Foster et al., Journal of the Science of Food and Agriculture, 2013, Effect of vegetarian diets on zinc status
• Thomson et al., American Journal of Clinical Nutrition, 2008, Brazil nuts: an effective way to improve selenium status
• Case report, Cureus, 2024, Hypothyroidism due to seaweed overconsumption
• Lausanne cross-sectional study on iodine status in the population, 2025
• Study on the effect of processing methods on mineral bioaccessibility in common beans, 2026