Which supplements are genuinely needed?

Use reliable B12-fortified foods or supplements. Vitamin D and iodine may need supplementation depending on exposure and intake; algae oil is an option for direct EPA/DHA.

How do I raise iron absorption?

Pair iron-rich foods with vitamin C, soak or sprout legumes, use leavened or sourdough bread, and keep tea and coffee to between meals.

Is seaweed a safe iodine source?

Only in measured amounts. Kelp in particular can exceed safe upper limits many times over in a single serving.

Do I need a calcium supplement?

Check total calcium intake against your age-specific target. Fortified milk and calcium-set tofu help, but two glasses or one tofu serving may not meet the full daily requirement.

What blood tests are worth doing?

Ask a clinician about tests based on symptoms and risk factors. B12 with MMA when indicated, ferritin for suspected iron deficiency, and targeted vitamin D or thyroid tests may be useful.

All guidesNutrition science11 min read

Iron, zinc, iodine, omega-3 and calcium without animal products

Five nutrients deserve attention on a plant-based diet. None require animal foods — they require knowing the absorption rules.

In short

Non-haem iron absorbs less efficiently, and vitamin C at the same meal raises absorption several-fold while tea and coffee lower it.
Iodine deserves attention: use measured iodised salt or a suitable supplement, not seaweed of unknown potency.
Algae oil supplies EPA and DHA directly, bypassing poor ALA conversion.
Fortified plant milk, calcium-set tofu and low-oxalate greens meet calcium needs comfortably.

Key numbers

Variable

Iron absorption increase with vitamin C at the same meal

Hallberg et al.

150 µg

Adult daily iodine requirement

WHO

250 mg

Common daily algae-oil EPA+DHA target

EFSA guidance

Varies

Calcium in tofu depends on coagulant and product

USDA

Iron: quantity is easy, absorption is the lever

Plant foods supply plenty of iron — lentils, tofu, pumpkin seeds, oats, dried apricots — but as non-haem iron, whose uptake is regulated by the body and modified by the meal around it. Vitamin C, citric acid and fermentation raise it; phytate, calcium supplements, tea and coffee lower it. Practically: put lemon, pepper or tomato with beans, and drink tea between meals rather than with them.

Soaking, sprouting and sourdough fermentation cut phytate substantially.
Cast-iron cookware measurably increases iron in acidic dishes.
Menstruating people have higher needs; check ferritin rather than guessing.

Zinc: same rules, smaller margin

Whole grains, legumes, seeds, tofu and cashews supply zinc alongside phytate. Soaking, fermentation and leavening can improve availability. People with high-phytate diets may need more zinc; the amount supplied by an extra serving depends on the food and portion.

Iodine: the genuinely overlooked one

Plant foods are low in iodine unless grown on iodine-rich soil, and most plant milks are unfortified. Iodised salt is the global public-health solution and works here too; a 150 µg supplement is an alternative. Seaweed is unreliable in the opposite direction — kelp can deliver thousands of micrograms and cause thyroid dysfunction.

Omega-3: skip the conversion problem

ALA from flax, chia and walnuts converts to EPA and DHA at low and variable rates. Algae oils supply DHA and, in some products, EPA directly. Check product content and quality testing; EFSA sets an adult adequate intake of 250 mg/day combined EPA and DHA.

Calcium and vitamin D

Fortified plant milks, calcium-set tofu, kale, bok choy and fortified juices can help meet calcium needs; check labels and portions. Spinach calcium is poorly absorbed because of oxalate. Vitamin D needs depend on sun exposure, age and other factors; UK guidance advises considering 400 IU daily in autumn and winter.

The data

Calcium per 100 g (USDA FoodData Central; fortified products vary by brand)

Firm tofu, calcium-set683 mg calcium
Tahini426 mg calcium
Soy drink124 mg calcium · calcium-fortified
Tempeh111 mg calcium
Chickpeas, boiled49 mg calcium

At a glance

Five nutrients: target, reliable sources, and the practical trick

Nutrient	Adult target	Plant sources	The trick
Iron	8–18 mg	Lentils, tofu, pumpkin seeds, oats	Add vitamin C; separate tea/coffee
Zinc	8–11 mg (+25–50%)	Beans, cashews, tempeh, oats	Soak, sprout, ferment
Iodine	150 µg	Iodised salt, supplement	Avoid unmeasured kelp
Omega-3 EPA/DHA	250 mg	Algae oil	Take with a fatty meal
Calcium	1,000–1,200 mg	Fortified milk, calcium-set tofu, kale	Shake the carton before pouring

Common objections

ClaimPlant iron is useless.

What the evidence showsIt absorbs less per milligram but the body upregulates uptake when stores are low, and vitamin C multiplies absorption at the same meal.

ClaimYou need fish for omega-3.

What the evidence showsFish obtain long-chain omega-3s through aquatic food webs. Algae oils can supply the same EPA and DHA molecules; choose products with appropriate quality testing.

ClaimSpinach is a great calcium source.

What the evidence showsIts calcium is bound to oxalate and largely unavailable. Kale, bok choy and fortified milks are the useful options.

Questions people ask

Which supplements are genuinely needed?: Use reliable B12-fortified foods or supplements. Vitamin D and iodine may need supplementation depending on exposure and intake; algae oil is an option for direct EPA/DHA.
How do I raise iron absorption?: Pair iron-rich foods with vitamin C, soak or sprout legumes, use leavened or sourdough bread, and keep tea and coffee to between meals.
Is seaweed a safe iodine source?: Only in measured amounts. Kelp in particular can exceed safe upper limits many times over in a single serving.
Do I need a calcium supplement?: Check total calcium intake against your age-specific target. Fortified milk and calcium-set tofu help, but two glasses or one tofu serving may not meet the full daily requirement.
What blood tests are worth doing?: Ask a clinician about tests based on symptoms and risk factors. B12 with MMA when indicated, ferritin for suspected iron deficiency, and targeted vitamin D or thyroid tests may be useful.