What nutrients may be lacking in the diet of those who practiced vegetarianism?

December 4, 2025 •

4 min read

According to one systematic review, individuals on plant-based diets often have lower intakes and status of nutrients like vitamin B12, vitamin D, and iron compared to meat-eaters. Understanding these potential nutritional gaps is crucial for maintaining a balanced and healthy vegetarian or vegan diet.

Quick Summary

This article explores potential nutrient deficiencies common in vegetarian and vegan diets, including vitamin B12, iron, calcium, and omega-3s. It details why these deficiencies occur, how they can impact health, and offers practical solutions for ensuring a nutritionally complete plant-based eating plan.

Key Points

Vitamin B12 Deficiency: Vitamin B12 is the most significant deficiency risk for vegetarians, especially vegans, as it is only naturally found in animal products.
Less Bioavailable Iron: The non-heme iron from plant sources is less readily absorbed than the heme iron from meat, requiring specific dietary strategies to maximize uptake.
Lower Calcium Intake: Vegans are particularly susceptible to low calcium intake without dairy, which can affect bone mineral density if not carefully managed with fortified foods and supplements.
Inefficient Omega-3 Conversion: Plant-based ALA omega-3s do not efficiently convert to the crucial EPA and DHA fatty acids, necessitating supplements from sources like algae.
Zinc Absorption Inhibitors: Compounds in plant foods like phytates reduce zinc absorption, potentially requiring a higher intake or supplementation to meet daily needs.
Fortification and Supplements are Key: Relying on fortified foods and targeted supplements for key nutrients like B12, vitamin D, and omega-3s is a reliable strategy for a complete vegetarian diet.

Common Nutrients of Concern for Vegetarians

While vegetarian diets offer numerous health benefits, certain nutrients that are abundant in animal products can be less bioavailable or absent in plant-based sources. Careful meal planning, fortification, and supplementation are therefore essential to prevent deficiencies. This guide details the key nutrients to monitor and provides strategies for adequate intake.

Vitamin B12 (Cobalamin)

Vitamin B12 is synthesized by microorganisms and is naturally present only in animal products. This makes deficiency a significant risk for both vegetarians and especially vegans. A lack of B12 can lead to serious neurological damage, megaloblastic anemia, and impaired nerve function. The issue is particularly critical for pregnant and lactating women, as deficiency can harm infant development.

Reliable sources for vegetarians

Fortified Foods: Many plant-based products, such as cereals, nutritional yeast, and plant milks, are fortified with vitamin B12.
Supplements: Oral supplements are the most reliable and efficient way to prevent and treat deficiency. Recommendations for adults often range from 50–100 mcg daily or 2000 mcg weekly.
Dairy and Eggs: Lacto-ovo vegetarians can obtain B12 from eggs and dairy, but this may not be enough, and absorption can be affected by cooking.

Iron

Plant-based diets often contain high amounts of iron, but it is in the form of non-heme iron, which is less easily absorbed by the body than the heme iron found in meat. Inhibitors like phytates and polyphenols can further reduce absorption. Lower iron stores are common in vegetarians, although severe iron deficiency anemia is not widespread.

Maximizing iron absorption

To boost the absorption of non-heme iron, vegetarians should pair iron-rich foods with vitamin C sources.

Iron-rich foods: Lentils, chickpeas, beans, spinach, kale, fortified cereals, and whole grains.
Vitamin C sources: Bell peppers, broccoli, citrus fruits, and strawberries.
Absorption tips: Soaking and sprouting legumes and grains and avoiding tea and coffee around mealtimes can improve iron uptake.

Calcium

Calcium intake can be a concern for vegetarians, particularly vegans who do not consume dairy products. Calcium is vital for bone health, and inadequate intake combined with low vitamin D levels can increase the risk of fractures and osteoporosis. While many plant foods contain calcium, their bioavailability varies significantly.

Bioavailability of calcium from different sources

High bioavailability (40–50%): Low-oxalate green leafy vegetables like kale, bok choy, and Chinese mustard greens.
Good bioavailability (30–40%): Calcium-fortified tofu and plant-based milks.
Moderate bioavailability (approx. 20%): Many legumes and beans.
Low bioavailability (approx. 5%): High-oxalate foods like spinach and rhubarb.

Omega-3 Fatty Acids

Omega-3 fatty acids, specifically eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are crucial for brain and heart health. While vegetarians get alpha-linolenic acid (ALA) from plant sources like flaxseed, walnuts, and chia seeds, the conversion of ALA to EPA and DHA in the body is highly inefficient. This results in lower levels of EPA and DHA in vegetarians compared to omnivores.

Vegetarian sources of omega-3s

ALA sources: Flaxseeds, chia seeds, walnuts, and canola oil.
Direct EPA and DHA source: Algal oil supplements are a reliable way to get preformed EPA and DHA without consuming fish.

Zinc

Zinc is important for immune function, wound healing, and growth. Like iron, zinc absorption from plant foods is hindered by phytates, meaning vegetarians may require up to 50% more zinc than meat-eaters. Lower serum zinc levels have been observed in many vegetarians and vegans.

Zinc-rich plant foods

Legumes: Lentils, chickpeas, and beans.
Nuts and Seeds: Cashews, pumpkin seeds, and almonds.
Grains: Fortified cereals, oats, and whole grains.
Fermented soy: Tempeh and miso can enhance absorption.

Conclusion: Strategic Planning is Key

A well-planned vegetarian or vegan diet can be nutritionally adequate, but it requires paying close attention to specific nutrients often found more readily in animal products. By incorporating fortified foods and, where necessary, supplements, individuals can avoid common deficiencies like those of vitamin B12, iron, calcium, and omega-3s. Consulting with a registered dietitian can be beneficial for those transitioning to a plant-based diet to ensure all nutritional needs are met. For more authoritative guidance on dietary reference intakes, consult reliable sources like the NIH.


Nutrient	Why it may be lacking in a vegetarian diet	How to ensure adequate intake
Vitamin B12	Not naturally found in plants, only in animal products.	Fortified foods (plant milks, nutritional yeast) and oral supplements.
Iron	Plant-based (non-heme) iron is less bioavailable; absorption is inhibited by phytates.	Pair iron-rich plant foods with Vitamin C. Use iron-fortified foods and supplements if needed.
Calcium	Common sources are dairy products; plant calcium's bioavailability varies greatly.	Consume calcium-fortified plant milks, tofu, and low-oxalate greens like kale.
Omega-3s (DHA/EPA)	Inefficient conversion of plant-based ALA to active EPA and DHA.	Use algal oil supplements to get direct DHA and EPA.
Zinc	Absorption is reduced by phytates in legumes, grains, and seeds.	Include zinc-rich plant foods like legumes, nuts, and fermented soy; consider supplements.

Frequently Asked Questions

No, it is very difficult for vegetarians, and nearly impossible for vegans, to get sufficient vitamin B12 from unfortified plant foods alone. The most reliable sources are fortified foods and supplements.

Plant-based iron is non-heme iron, which is not absorbed as well as the heme iron from meat. Furthermore, plant compounds like phytates can inhibit absorption.

Since the body is inefficient at converting plant-based ALA to EPA and DHA, the best direct source for vegetarians and vegans is an algal oil supplement.

No, the bioavailability of calcium varies. Some greens like kale have high bioavailability, while others like spinach, which contain oxalates, have very low absorption.

Pairing iron-rich foods with sources of vitamin C, such as bell peppers or citrus fruits, can significantly increase the absorption of non-heme iron.

Excellent plant sources of zinc include legumes (lentils, chickpeas), nuts (cashews, almonds), seeds (pumpkin, sunflower), and fermented soy products like tempeh.

It depends on the individual's diet. While vitamin B12 supplementation is generally recommended for all vegans and most vegetarians, others like iron and calcium may be manageable through careful food choices, fortified products, and absorption-enhancing techniques. A healthcare provider or dietitian can provide personalized guidance.