Which nutrient is most likely to be lacking in the diet of vegetarians?

October 25, 2025 •

4 min read

According to a systematic review published in the European Journal of Nutrition, a high prevalence of vitamin B12 deficiency has been observed in individuals consuming plant-based diets. The nutrient most likely to be lacking in the diet of vegetarians, especially vegans, is vitamin B12, since it is found naturally almost exclusively in animal products.

Quick Summary

Vegetarians and vegans face a higher risk of vitamin B12 deficiency because this nutrient is primarily found in animal products. Careful meal planning, fortified foods, and supplementation are necessary to ensure adequate intake and prevent serious neurological and hematological issues.

Key Points

Vitamin B12 is the primary concern: As it is found naturally almost exclusively in animal products, vegetarians and especially vegans are at high risk of deficiency.
Deficiency symptoms can be delayed: The body's ability to store B12 means symptoms of deficiency can take years to appear, masking the problem until it becomes severe.
Fortification and supplements are key: The most reliable ways for vegetarians to get sufficient B12 are through fortified foods like cereals and plant-based milks, or a daily supplement.
Iron absorption needs a boost: Non-heme iron from plant sources is less bioavailable. Pairing iron-rich plant foods with vitamin C-rich foods significantly improves absorption.
Zinc and phytates: Phytates in legumes and whole grains can inhibit zinc absorption, making soaking, sprouting, and fermentation helpful for increasing bioavailability.
Consider all micronutrients: While B12 is the most likely to be lacking, vegetarians should also pay attention to intake of iron, zinc, calcium, and vitamin D.
Consult a professional for personalized advice: A registered dietitian can provide a tailored plan to ensure a nutritionally complete vegetarian diet.

Vitamin B12: Why Vegetarians Are at Risk

Vitamin B12, or cobalamin, is an essential water-soluble vitamin required for red blood cell formation, neurological function, and DNA synthesis. While lacto-ovo vegetarians (who consume dairy and eggs) have some dietary sources, the levels are often insufficient or less bioavailable than in meat. Strict vegetarians and vegans are particularly vulnerable to deficiency, as plant foods are not a reliable source.

Unlike many other vitamins, the body can store a several-year supply of vitamin B12 in the liver. This can mask a developing deficiency, with symptoms potentially taking years to appear. This prolonged latent period makes consistent intake, rather than relying on existing stores, critical for long-term health.

Consequences of Vitamin B12 Deficiency

A prolonged or severe deficiency in vitamin B12 can lead to serious health problems, including megaloblastic anemia, which causes extreme tiredness and a lack of energy. It can also result in irreversible nerve damage, with symptoms such as numbness, tingling in the hands and feet, muscle weakness, and problems with memory and balance.

For pregnant or breastfeeding women on vegetarian diets, inadequate B12 intake is particularly dangerous as it can affect infant neurological development. Therefore, careful attention to this nutrient is crucial for all stages of life.

Strategies to Ensure Adequate B12 Intake

For vegetarians, especially vegans, relying solely on plant-based foods for vitamin B12 is risky. A planned approach incorporating fortified products and supplements is often necessary.

Reliable Sources of Vitamin B12 for Vegetarians:

Fortified foods: Look for breakfast cereals, nutritional yeast, and plant-based milks (soy, almond, rice) that are fortified with vitamin B12.
Supplements: Regular B12 supplements are a dependable way to meet the recommended daily intake. For many, a daily or weekly supplement is recommended.
Dairy and eggs: Lacto-ovo vegetarians can get some B12 from milk, cheese, and eggs, though often not enough to meet all requirements.

Other Nutrients of Concern for Vegetarians

While vitamin B12 is the primary concern, other nutrients also require attention in a vegetarian diet due to varying bioavailability or primary sources being animal-based. These include iron, zinc, iodine, and vitamin D.

Iron

Iron from plant-based sources (non-heme iron) is less easily absorbed by the body than heme iron from meat. Vegetarians can compensate by consuming plenty of iron-rich plant foods and enhancing absorption.

Tips for Increasing Iron Absorption:

Combine iron-rich plant foods with sources of vitamin C, such as citrus fruits, bell peppers, and tomatoes.
Avoid drinking tea or coffee with meals, as tannins can inhibit iron absorption.
Soak and sprout legumes and grains to reduce phytate levels, which can also hinder absorption.

Zinc

Zinc, vital for immune function and cell growth, can also be less bioavailable from plant-based sources due to phytates. While many plant foods contain zinc, vegetarians often have lower serum zinc levels.

Enhancing Zinc Intake:

Include legumes, nuts, seeds, and whole grains in your diet.
Soaking, sprouting, and fermenting can help increase zinc bioavailability.
Certain fermented foods like tempeh and miso can enhance zinc absorption.

Vitamin D and Calcium

While many vegetarians consume dairy, vegans must rely on fortified plant-based milks and other sources for calcium and vitamin D. Sunlight exposure is the primary natural source of vitamin D, but geographical location, season, and skin pigmentation can limit its effectiveness.

Comparison Table: Key Nutrients for Vegetarians


Nutrient	Primary Challenge for Vegetarians	Reliable Plant-Based Sources	Fortified Products & Supplements
Vitamin B12	Found almost exclusively in animal products; deficiency can be masked for years.	Unreliable. Some algae may contain inactive analogues.	Supplements, fortified cereals, and plant-based milks.
Iron	Non-heme iron from plants is less bioavailable than heme iron from meat.	Legumes, tofu, dark leafy greens, nuts, seeds, dried fruits.	Iron-fortified cereals.
Zinc	Absorption is inhibited by phytates in plant foods.	Legumes, nuts, seeds, whole grains.	Zinc supplements, fortified cereals.
Calcium	Often less available for vegans who don't consume dairy.	Leafy greens, calcium-set tofu, sesame seeds, pulses.	Fortified plant-based milks and orange juice.
Vitamin D	Limited natural dietary sources; depends on sun exposure.	UV-exposed mushrooms.	Supplements, fortified plant-based milks, and cereals.

Conclusion: The Importance of Planning

A well-planned vegetarian diet can provide all the necessary nutrients for good health, but it requires awareness and attention to key nutrients like vitamin B12. For most vegetarians, especially those following a strict plant-based diet, supplementation or consistent use of fortified foods is essential to prevent deficiency. Awareness of the differences in absorption for nutrients like iron and zinc also helps ensure adequate intake. By understanding the potential nutritional gaps and how to address them, vegetarians can enjoy a healthy and sustainable lifestyle. Seeking advice from a registered dietitian is always recommended for personalized dietary planning.

Frequently Asked Questions

The nutrient most likely to be lacking in a vegetarian's diet is vitamin B12, as it is found naturally almost exclusively in animal products like meat, eggs, and dairy.

No, plant foods are not a reliable source of active vitamin B12. While some plant-based foods may claim to contain B12, they often contain inactive analogues that cannot be used by the body and can interfere with absorption.

Symptoms can include extreme tiredness, lack of energy, muscle weakness, and neurological problems like pins and needles, impaired memory, and difficulty with balance.

To increase iron intake, vegetarians should combine iron-rich plant foods like lentils, tofu, and leafy greens with vitamin C-rich foods such as bell peppers or citrus fruits, which significantly enhances absorption.

Zinc absorption from plant foods is less efficient than from animal products due to the presence of phytates, which can bind to the mineral. This can lead to lower overall zinc levels in vegetarians.

Vegetarians can get vitamin D from safe sun exposure, UV-exposed mushrooms, and fortified foods like cereals and plant-based milks. Supplements are also a common and reliable option, especially in winter.

Yes, aside from B12, iron, and zinc, other potential nutrients of concern include iodine and omega-3 fatty acids, which require mindful planning to ensure adequate intake.