Are there negative effects of being vegetarian?

October 25, 2025 •

5 min read

While vegetarian diets are often praised for their health benefits, research shows potential downsides. A 2019 study published in The BMJ revealed a 20% higher stroke risk in vegetarians compared to meat-eaters, highlighting potential negative effects of being vegetarian if not properly managed. This underscores the importance of understanding and addressing potential nutritional risks.

Quick Summary

Although vegetarian diets can be healthy, improper planning may lead to deficiencies in key nutrients like B12, iron, and calcium. Potential risks related to bone health and stroke have also been identified, requiring careful dietary management and supplementation.

Key Points

Nutrient Deficiencies: Vegetarians are at risk of deficiencies in Vitamin B12, iron, calcium, Vitamin D, omega-3s, and zinc, which require careful dietary planning.
Bone Health Concerns: Vegans, and sometimes vegetarians, have been linked to lower bone mineral density and higher fracture rates due to inadequate calcium and vitamin D.
Stroke Risk Association: Observational studies have found a higher risk of hemorrhagic stroke among vegetarians, possibly linked to low B12 or LDL cholesterol.
Impact on Mental Health: Some studies suggest higher rates of anxiety and depression among vegetarians, though research is conflicting and often linked to nutritional gaps or other factors.
Processed Food Pitfalls: An unhealthy vegetarian diet can rely on processed meat substitutes high in sodium and unhealthy fats, negating many health benefits.
Requires Active Management: To be healthy, a vegetarian diet must be appropriately planned to include diverse protein sources, supplements (especially B12), and nutrient-fortified foods.

Understanding the Nutritional Shortcomings

Transitioning to a vegetarian diet can bring numerous health benefits, including lower rates of heart disease and type 2 diabetes. However, simply removing meat without proper planning can lead to significant nutritional shortfalls. It is crucial to understand and actively manage these risks to maintain a healthy, balanced diet. The potential negative effects of being vegetarian often stem from the removal of animal products, which are primary sources for certain vitamins and minerals.

Vitamin B12: The Most Significant Concern

Vitamin B12 is essential for nerve function and red blood cell production. It is found almost exclusively in animal products. As a result, vegetarians and especially vegans are at high risk of deficiency if they don't consume fortified foods or supplements. A deficiency can lead to anemia and even irreversible neurological damage. Supplementation is considered essential for those who restrict animal products to this extent.

Iron: Bioavailability Matters

Plant-based diets often have sufficient iron content, but the body absorbs non-heme iron from plants less efficiently than the heme iron found in meat. Phytates in whole grains and legumes can also inhibit absorption. This can lead to lower iron stores and a higher risk of iron deficiency anemia in vegetarians. Fortunately, consuming iron-rich plant foods with sources of vitamin C can significantly improve absorption.

Calcium, Vitamin D, and Bone Health

Both vegetarians and vegans, especially those who exclude dairy, are at risk for low calcium and vitamin D intake. Vitamin D is also critical for calcium absorption. Studies show that vegans and sometimes vegetarians have lower bone mineral density (BMD) and a higher risk of fractures. This risk is most pronounced in vegans with a low body mass index (BMI). To counter this, it's vital to focus on calcium-fortified plant milks, low-oxalate leafy greens, and ensure adequate vitamin D through sunlight or supplements.

Omega-3 Fatty Acids and Brain Health

Vegetarian and vegan diets are often low in long-chain omega-3 fatty acids, EPA and DHA, which are primarily found in fish and eggs. While the body can convert the plant-based omega-3 (ALA) from sources like walnuts and flaxseed, the conversion rate is low. This can lead to lower blood levels of EPA and DHA, which are important for cardiovascular and cognitive health. Supplements derived from algae offer a direct source of these fatty acids.

Other Nutrient Concerns

Zinc: Phytates in whole grains, seeds, and legumes reduce zinc absorption, though most Western vegetarians don't appear to be deficient.
Iodine: While intake is often adequate for lacto-ovo vegetarians who consume dairy, vegans may have low iodine status, particularly if they do not use iodized salt or consume sea vegetables.
Protein: While most plant-based diets provide adequate protein, particularly if overall calorie intake is sufficient, it requires consuming a variety of plant protein sources throughout the day to get all essential amino acids. Vegans may be at higher risk for lower protein intake.

The Risks of a Poorly Planned Vegetarian Diet

A vegetarian diet does not automatically equate to a healthy one. A diet of processed carbs, sugary snacks, and fatty cheese pizza is technically vegetarian but nutritionally unsound. Here are some pitfalls to avoid:

Reliance on Processed Foods: Many meat substitutes and other vegetarian convenience foods are high in sodium, sugar, and unhealthy fats. It’s easy to swap meat for processed items that offer little nutritional value and can increase health risks.
Increased Bloating and Gas: For new vegetarians, the sudden increase in dietary fiber from beans, lentils, and vegetables can cause temporary digestive discomfort. It is best to increase fiber intake gradually.
Potential for Stroke Risk: As noted in the introduction, the EPIC-Oxford study found a higher risk of stroke, particularly hemorrhagic stroke, among vegetarians. The reasons are not yet fully understood but may relate to low vitamin B12 and potentially low LDL cholesterol levels. This highlights the need for balanced nutrition and supplements to manage potential risks.
Mental Health Links: While studies are conflicting, some research suggests a link between vegetarianism and higher rates of depression and anxiety. Low levels of omega-3 fatty acids or deficiencies in B vitamins may play a role.

Comparison: Risks & Management


Health Aspect	Omnivore Diet	Lacto-Ovo Vegetarian Diet	Vegan Diet
Vitamin B12	Easily obtained from meat/dairy.	Can be obtained from dairy/eggs, but lower intake is common.	High deficiency risk; supplementation needed.
Iron	High heme iron absorption.	Lower non-heme iron absorption; must pair with Vitamin C.	Lower non-heme iron absorption; must pair with Vitamin C.
Calcium & Vit D	Adequate intake is common (dairy, eggs).	Adequate intake is common if dairy/eggs are included.	Low intake and status; requires fortification or supplementation.
Omega-3s (DHA/EPA)	Good sources in fish, some eggs.	Low intake without specific fortified products or supplements.	Very low intake; requires supplementation or fortified foods.
Protein	Easily obtained from animal sources.	Easily obtained with dairy/eggs and varied plant proteins.	Can be low if not carefully planned; relies on diverse plant sources.
Bone Health	Typically higher BMD due to higher calcium, D, and protein intake.	Moderate risk of lower BMD, less severe than vegans.	Higher fracture risk, especially with low BMI; low BMD.

Mitigating the Risks of a Vegetarian Diet

Becoming a healthy vegetarian requires intentional meal planning. Simply removing meat is not enough; you must replace those nutrients with thoughtful, plant-based choices.

Here's how to manage the potential negative effects:

Prioritize Diverse Protein: Include a wide variety of protein sources, such as beans, lentils, tofu, tempeh, nuts, and seeds throughout the day. Quinoa and soy are complete proteins, but variety ensures all amino acids are consumed.
Supplement Wisely: A vitamin B12 supplement is highly recommended for all vegetarians, and essential for vegans. Vitamin D supplementation may also be necessary, especially for those with limited sun exposure. Consult with a doctor or dietitian before starting new supplements.
Enhance Iron Absorption: Combine iron-rich plant foods like spinach and lentils with vitamin C sources such as citrus fruits, peppers, and broccoli. Avoid drinking tea or coffee during meals, as they can inhibit iron absorption.
Boost Calcium Intake: For vegans, consume calcium-fortified plant milks, calcium-set tofu, and low-oxalate greens like kale and bok choy. Ensure sufficient vitamin D intake to help with absorption.
Seek Omega-3 Sources: Include flaxseeds, chia seeds, walnuts, and canola oil in your diet for ALA. Vegans should consider an algae-based DHA/EPA supplement to ensure adequate long-chain omega-3 intake.
Limit Processed Foods: Read labels carefully and limit consumption of ultra-processed meat alternatives high in sodium, added sugar, and unhealthy fats.

Conclusion

While vegetarian diets can be a healthy and ethical choice, they are not without potential pitfalls. The negative effects of being vegetarian most often arise from poor dietary planning, leading to deficiencies in critical nutrients such as B12, iron, calcium, vitamin D, and omega-3s. These deficiencies can contribute to health issues like anemia, reduced bone mineral density, and potentially impact neurological and cardiovascular health. However, with careful planning, conscious food choices, and appropriate supplementation, these risks can be effectively managed. A well-balanced and varied vegetarian diet can be nutritionally adequate and support long-term health. Consulting a registered dietitian can be invaluable for ensuring a safe and complete transition. Link: How to Maintain a Balanced Diet as a Vegetarian or Vegan

Frequently Asked Questions

Vitamin B12 deficiency is often considered the most significant risk, as this nutrient is found almost exclusively in animal products. Vegetarians and vegans must obtain B12 through fortified foods or supplements to prevent severe neurological problems and anemia.

While plant-based foods contain iron (non-heme), it is less efficiently absorbed than the heme iron from meat. To maximize absorption, vegetarians should pair iron-rich plant foods like lentils and spinach with a source of vitamin C.

Studies have shown that vegans, and to a lesser extent vegetarians, can have lower bone mineral density (BMD) and a higher risk of fractures. This is often linked to inadequate intake of calcium and vitamin D.

Some research suggests an association between vegetarianism and higher rates of depression and anxiety. This could be related to nutrient deficiencies, such as omega-3 fatty acids or B vitamins, but more research is needed, and lifestyle factors play a role.

Unlike animal sources, most plant foods are not 'complete' proteins. By eating a variety of protein-rich plant foods throughout the day, such as beans, lentils, nuts, and seeds, vegetarians can ensure they receive all the essential amino acids.

Yes. A vegetarian diet is only as healthy as the foods you choose. Relying on highly processed junk foods, sugary snacks, and unbalanced meat substitutes can lead to poor nutrition and associated health risks.

For those new to vegetarianism, the significant increase in fiber from fruits, vegetables, and legumes can cause bloating and gas. It is advisable to increase fiber intake gradually to allow the digestive system to adjust.

Supplementation is crucial for certain nutrients. A reliable source of vitamin B12 is essential for all vegetarians and vegans. Depending on diet and lifestyle, supplements for vitamin D, omega-3s, and possibly iodine may also be necessary.