Vegans are most likely to fall short on vitamin B12, omega-3 fatty acids (specifically EPA and DHA), vitamin D, iron, zinc, iodine, and selenium. Some of these gaps are easy to close with a daily supplement. Others require more attention to how you prepare and combine foods, because plant-based versions of certain nutrients are harder for your body to absorb.
None of these shortfalls are inevitable. But they do require awareness, especially during the first year or two of eating fully plant-based, before the habits become automatic.
Vitamin B12
This is the one nutrient you cannot get from whole plant foods in any meaningful amount. B12 is produced by bacteria and concentrated in animal tissues, so vegans have a genuinely higher risk of deficiency. The adult recommended intake is 2.4 mcg per day, and without supplementation or fortified foods, stores gradually deplete over months to years. Early symptoms include fatigue, tingling in the hands and feet, and difficulty concentrating. Left unchecked, deficiency can cause lasting nerve damage.
Fortified nutritional yeast, fortified plant milks, and B12 supplements all work well. Many vegans take a daily supplement of 25 to 100 mcg or a weekly dose of 1,000 to 2,000 mcg, since your body only absorbs a small fraction at a time. This is the single most important supplement for anyone eating entirely plant-based.
Omega-3 Fatty Acids
Plant foods like flaxseed, chia seeds, and walnuts provide ALA, a type of omega-3. But your body needs to convert ALA into two longer-chain forms, EPA and DHA, which support brain function, eye health, and inflammation regulation. That conversion is inefficient. In men, roughly 8% of ALA converts to EPA and somewhere between 0% and 4% becomes DHA. Women convert more, around 21% to EPA and 9% to DHA, likely due to the influence of estrogen.
Those numbers mean that even if you eat plenty of flax and walnuts, you may still run low on DHA in particular. Algae-based EPA and DHA supplements bypass the conversion problem entirely. Algae is where fish get their omega-3s in the first place, so these supplements provide the same fatty acids without the middleman.
Iron Absorption on a Plant-Based Diet
Vegans often eat as much or more total iron than meat eaters. The issue isn’t quantity. It’s the type. Plant foods contain non-heme iron, which your gut absorbs less readily than the heme iron found in meat. And certain compounds in plant foods actively block absorption. Phytates, found naturally in grains, beans, nuts, and seeds, are the biggest culprit. Research on wheat rolls showed that just 2 mg of phytate reduced iron absorption by 18%, while 250 mg cut it by 82%.
Vitamin C is the most powerful counterweight. Adding it to a meal can increase non-heme iron absorption up to sixfold. That means squeezing lemon over lentils, eating bell peppers alongside beans, or having strawberries with oatmeal all make a real difference. The vitamin C needs to be eaten at the same meal, though. Taking it hours before is far less effective.
Coffee, tea, and calcium-rich foods also reduce iron absorption when consumed at the same time as iron-rich meals. Spacing these out helps. If you’re prone to low iron (common in menstruating women), periodic blood work is a smart idea rather than supplementing blindly, since excess iron carries its own risks.
Zinc and How to Improve It
Zinc faces the same phytate problem as iron. The World Health Organization recognizes this directly, recommending higher zinc intakes for people eating plant-based diets compared to meat-based diets. In India, where plant-heavy diets are common, the recommended daily intake is set at 17 mg for men and 13.2 mg for women, notably higher than in many Western countries.
Good vegan sources include pumpkin seeds, chickpeas, lentils, cashews, oats, and tofu. But the real leverage comes from food preparation. Soaking beans before cooking meaningfully reduces phytate levels. Fermentation is even more effective. Research on fermented grain bread found that 72 hours of fermentation increased zinc bioavailability by 63% compared to unfermented grain. You don’t need to ferment everything for three days, but regularly including sourdough bread, tempeh, miso, and other fermented foods gives your body better access to the zinc already in your diet.
Vitamin D
Vitamin D deficiency is widespread regardless of diet, but vegans face an extra challenge because the most common dietary sources are fatty fish, egg yolks, and fortified dairy. Vitamin D2, the form traditionally found in plant foods and supplements, is less effective at raising blood levels than vitamin D3. One clinical trial found a single dose of D3 was roughly twice as effective as D2. Vitamin D2 supplements also degrade more easily with humidity and temperature changes during storage.
The good news is that vegan-friendly D3 now exists, sourced from lichen (a symbiotic organism of fungus and algae). If you’re choosing a vitamin D supplement, lichen-based D3 is a better option than D2 for maintaining adequate blood levels over time. Sun exposure also produces D3 in your skin, but if you live at a northern latitude, have darker skin, or spend most of your day indoors, you likely need a supplement regardless.
Iodine
In omnivore diets, iodine typically comes from dairy products, seafood, and iodized salt. Vegans who don’t use iodized salt and don’t eat seaweed can easily fall below the adult recommendation of 150 mcg per day. Iodine is essential for thyroid function, and prolonged deficiency can lead to fatigue, weight changes, and an enlarged thyroid gland.
Seaweed is the most concentrated plant source, but it comes with a catch: iodine content varies wildly by type. A single gram of dried brown seaweed (like kelp) can exceed the European upper tolerable daily limit of 600 mcg, while the same amount of green or red seaweed might provide only a fraction of the daily requirement, sometimes requiring up to 6 grams to meet it. This makes seaweed unreliable as a sole iodine source unless you know exactly what variety you’re eating and how much iodine it contains.
For consistency, a small daily supplement or regular use of iodized salt is more practical. Half a teaspoon of iodized salt provides roughly 150 mcg, which covers the daily target.
Selenium
Selenium is a trace mineral involved in thyroid metabolism and antioxidant defense. Your daily need is modest: 55 to 70 mcg depending on age and sex, with an upper safe limit of 400 mcg. Brazil nuts are famously rich in selenium, but their content is extraordinarily variable depending on where they were grown. Research analyzing nuts from different Brazilian states found that a single nut could provide anywhere from 11% to 288% of the daily requirement. Across South America more broadly, selenium concentrations in Brazil nuts span three orders of magnitude.
This means one or two Brazil nuts a day might be perfect, or it might push you toward excess. Symptoms of too much selenium include hair loss, brittle nails, skin lesions, and in extreme cases, nervous system damage. If you rely on Brazil nuts, eating one to three per day from a consistent source is a reasonable approach. Other plant sources like whole grains, sunflower seeds, and mushrooms contribute smaller amounts that add up over the course of a day.
Protein Quality and Lysine
Total protein is rarely a problem on a well-planned vegan diet. The more relevant concern is lysine, an essential amino acid that’s less abundant in grains and nuts than in animal foods. The daily lysine requirement ranges from about 1,700 to 3,500 mg depending on body size, and it’s genuinely difficult to meet without intentionally including high-lysine plant foods.
The best sources, each providing at least 350 mg per serving, are beans (chickpeas, kidney, pinto, navy), lentils, split peas, and soy foods like tofu, tempeh, edamame, and soy milk. Peanuts also contribute meaningfully. If your meals regularly feature at least two or three servings from this list throughout the day, lysine needs are typically covered. A diet built mostly around rice, bread, and vegetables without legumes or soy is where lysine gaps appear.
Putting It Together
The nutrients vegans need to watch fall into two categories. Vitamin B12 and omega-3 DHA are nearly impossible to get from whole plant foods alone, so supplementation is the straightforward solution. The rest (iron, zinc, iodine, selenium, vitamin D, and lysine) are available in plant foods but require some combination of choosing the right sources, preparing foods to improve absorption, and in some cases, supplementing when diet alone falls short.
A daily B12 supplement, an algae-based omega-3, vitamin D3 from lichen, and regular use of iodized salt cover the biggest gaps with minimal effort. From there, building meals around legumes, eating vitamin C alongside iron-rich foods, and incorporating fermented or soaked grains and beans takes care of most of the rest.