Vegetarians are most commonly low in vitamin B12, iron, omega-3 fatty acids, vitamin D, zinc, iodine, and calcium. Some of these gaps are straightforward to close with the right food choices, while others are nearly impossible to fill without supplements or fortified foods. The specific risks depend on whether you eat eggs and dairy or avoid all animal products entirely.
Vitamin B12: The Biggest Gap
B12 is the single most important nutrient for vegetarians to pay attention to. It occurs naturally almost exclusively in animal foods, and the body can’t make it. Among vegetarians, reported deficiency rates range from 6% to 14%, and among vegans, that number jumps to as high as 52%. Even more striking: when researchers used a broader threshold for insufficiency (not outright deficiency, but levels low enough to cause problems over time), up to 75% of vegetarian women of childbearing age fell short.
Your body stores B12 for years, so deficiency creeps up slowly. Early signs are the typical symptoms of anemia: fatigue, paleness, shortness of breath, headaches, and dizziness. Left unchecked, B12 deficiency starts affecting the brain and nervous system, causing tingling or pain in the hands and feet, trouble walking, confusion, memory problems, mood changes, and even vision issues. A smooth, painful red tongue is another hallmark.
Lacto-ovo vegetarians get some B12 from eggs and dairy, but often not enough for optimal levels. Fortified nutritional yeast is one of the most reliable plant-based sources: about two tablespoons provides the full recommended daily amount of 2.4 micrograms for adults. Fortified plant milks and cereals help, too. For vegans especially, a B12 supplement is not optional.
Iron: Plenty in Plants, Poorly Absorbed
Vegetarians can get iron from beans, lentils, spinach, nuts, and fortified grains, but the type of iron in plants (non-heme iron) absorbs far less efficiently than the type in meat (heme iron). About 25% of heme iron from animal foods gets absorbed, compared to 17% or less of non-heme iron. When you look at overall diet patterns, iron bioavailability drops to just 5% to 12% for plant-based eaters, versus 14% to 18% for omnivores.
This means vegetarians need to eat significantly more iron-rich foods to reach the same effective intake. Pairing iron-rich foods with vitamin C (citrus, bell peppers, tomatoes) boosts absorption substantially. On the flip side, drinking tea or coffee with meals can inhibit it. Premenopausal women who are vegetarian face the highest risk, since menstruation increases iron needs on top of already lower absorption.
Omega-3 Fatty Acids: A Conversion Problem
The omega-3 fats your body actually uses for brain function, heart health, and controlling inflammation are EPA and DHA. These come primarily from fatty fish. Plants provide a precursor called ALA (found in flaxseeds, chia seeds, walnuts, and hemp seeds), but your body has to convert ALA into the active forms, and it does this poorly. Men convert roughly 8% of ALA into EPA and essentially 0% into DHA. Women do better, converting about 21% to EPA and 9% to DHA, likely due to estrogen’s role in the process.
This means even if you eat plenty of flax and walnuts, your blood levels of EPA and DHA will typically be much lower than those of fish eaters. Algae-based supplements are the most direct vegetarian source of preformed DHA and EPA, since algae is where fish get their omega-3s in the first place.
Vitamin D: A Problem for Everyone, Worse for Vegetarians
Vitamin D deficiency is widespread regardless of diet, but vegetarians face an extra challenge. The two forms of supplemental vitamin D are D2 (from fungi and plants) and D3 (typically from animal sources like lanolin in sheep’s wool). Research shows D3 is more effective at raising blood levels of vitamin D, yet many vegetarian-friendly fortified foods contain D2.
Mushrooms exposed to UV light are one of the few natural plant sources of vitamin D. Fortified plant milks, orange juice, and cereals also provide D2. If you rely on these, you may need a higher intake to achieve the same blood levels as someone taking D3. Vegans who want D3 can look for supplements sourced from lichen, which is plant-based.
Calcium: It Depends on What You Eat
Lacto-ovo vegetarians who eat dairy regularly usually get enough calcium. The real issue is for those who don’t consume much dairy, or for vegans, because calcium absorption from plant foods varies wildly depending on the plant.
Spinach is often touted as calcium-rich, but your body absorbs only about 5% of its calcium due to high oxalate content. Chinese spinach and rhubarb fare only slightly better, at around 9%. Compare that to low-oxalate greens: kale and bok choy deliver roughly 50% to 53% calcium absorption, which is actually higher than dairy (about 30% to 35%). Broccoli falls in a similar range. So the key isn’t just eating calcium-rich plants; it’s eating the right ones. A cup of cooked kale or bok choy gives you far more usable calcium than the same amount of spinach.
Zinc: Hidden by Phytates
Zinc is found in legumes, whole grains, nuts, and seeds, all staples of a vegetarian diet. The problem is that these same foods are high in phytates, compounds that bind to zinc and block its absorption. This makes the zinc in plant foods less available to your body than the zinc in meat.
Traditional food preparation methods can help. Soaking beans and grains before cooking, sprouting seeds and lentils, and fermenting foods (like sourdough bread or tempeh) all break down phytates through enzyme activity, freeing up more zinc and iron for absorption. These aren’t minor tweaks. They can meaningfully shift how much of these minerals you actually get from your food.
Iodine: An Overlooked Risk
Iodine tends to fly under the radar, but vegetarian diets are consistently shown to fall short. Your thyroid needs iodine to function, and most people in Western countries get it from dairy, seafood, and iodized salt. Many common plant foods contain virtually zero iodine: beans, lentils, tofu, rice, and potatoes all register at 0 micrograms per serving. Even a soy-based veggie burger provides only about 5 micrograms, a fraction of the 150-microgram daily recommendation for adults.
Vegetarians and vegans, especially women, also tend to use less iodized salt and more sea salt or specialty salts, which contain almost no iodine (non-iodized sea salt provides just 0.02 micrograms per serving). Seaweed is sometimes suggested as a solution, and dried nori does provide about 116 micrograms per serving. But iodine content in seaweed varies enormously between species and batches. Kelp, for instance, can deliver up to a hundred times the daily recommendation in a single serving, risking iodine excess, which is also harmful to the thyroid. The safest approach is using iodized salt consistently or taking a supplement with a controlled dose.
A compounding factor: vegetarians who are also low in iron and selenium may experience worse thyroid consequences from iodine deficiency, since all three nutrients work together in thyroid hormone production.
Practical Priorities
Not all of these gaps carry equal urgency. B12 supplementation is essential for all vegetarians and non-negotiable for vegans, since the consequences of deficiency are serious and irreversible if caught late. Iron and zinc deserve attention through smart food pairing and preparation methods, with supplements considered if blood work shows low levels. Omega-3s from algae supplements are the most reliable way to get EPA and DHA without fish. For calcium, choosing low-oxalate greens over spinach makes a real difference. And checking that your salt is actually iodized is one of the simplest fixes on this list.