Understanding Your Body: Why do I not feel good on a vegan diet?

October 26, 2025 •

4 min read

Some studies indicate that vegans face a higher risk of deficiencies in key nutrients like Vitamin B12 and Iron, which can significantly impact energy and overall well-being. Understanding potential pitfalls is the first step in addressing your question: Why do I not feel good on a vegan diet?

Quick Summary

This guide explores common nutritional deficiencies, including B12, iron, and omega-3s, and diet planning mistakes, like inadequate calorie intake or reliance on processed foods, that can cause discomfort on a vegan diet. It also covers digestive adjustments and provides actionable steps for optimizing plant-based eating.

Key Points

Check for Deficiencies: Vitamin B12 is essential for vegans and requires supplementation, while iron from plant sources is less bioavailable and needs careful management.
Eat Enough Calories: Undereating is a common mistake on a plant-based diet due to lower caloric density, which can lead to fatigue and low energy levels.
Prioritize Whole Foods: Relying on processed vegan junk food instead of whole, nutrient-dense plants can compromise your health and leave you feeling poorly.
Address Digestive Changes: Increased fiber intake can cause temporary bloating and gas as your gut adapts; these symptoms often subside with time or can be managed with adjustments.
Consider Omega-3 and Vitamin D: Supplementation with algae-based omega-3 EPA/DHA and Vitamin D is often necessary to ensure adequate intake of these critical nutrients.
Seek Professional Advice: If symptoms persist, a blood test and consultation with a healthcare provider or registered dietitian can identify specific deficiencies or underlying issues.

Common Nutritional Reasons for Feeling Unwell on a Vegan Diet

Transitioning to a vegan diet can be a positive change, but it requires careful planning to ensure all nutritional needs are met. For those feeling unwell, often the culprit lies in specific nutrient gaps that arise from eliminating animal products without properly replacing them. Addressing these gaps is key to restoring your health and energy.

Vitamin B12 Deficiency

Vitamin B12 is arguably the most critical nutrient for vegans to monitor, as it is primarily found in animal products. It is vital for red blood cell formation, neurological function, and DNA synthesis. A deficiency can lead to a range of symptoms, including profound fatigue, weakness, nerve damage (pins and needles sensation), and memory issues.

The solution: Supplementation is essential for all vegans. Consistently consuming B12-fortified foods like nutritional yeast, plant milks, and breakfast cereals is also helpful.

Iron Deficiency

Iron deficiency is one of the world's most common nutritional shortfalls, and while a vegan diet can be rich in iron, the non-heme iron found in plants is less bioavailable than the heme iron from meat. This can lead to lower iron stores, especially in menstruating women and athletes. Low iron can cause fatigue, pale skin, weakness, and impaired immunity.

The solution: To maximize absorption, pair iron-rich plant foods with Vitamin C sources at the same meal. Sources include: citrus fruits, bell peppers, leafy greens, lentils, chickpeas, and fortified cereals. Avoid drinking coffee or tea within an hour of an iron-rich meal, as they can inhibit absorption.

Omega-3 Fatty Acid Imbalance

While plant-based diets provide alpha-linolenic acid (ALA) from sources like flax, chia, and walnuts, the conversion to the crucial longer-chain fatty acids EPA and DHA is inefficient, especially without sufficient zinc and B vitamins. This can impact brain function, heart health, and mood.

The solution: Regular consumption of ALA-rich foods is important, but supplementation with algae-based EPA and DHA oil is highly recommended, particularly for pregnant individuals and those with low energy.

Vitamin D and Calcium

Many vegans have lower intakes of Vitamin D and Calcium compared to non-vegans, which can impact bone density and increase fracture risk over time. Vitamin D is also critical for immune function.

The solution: Ensure adequate sun exposure and consider Vitamin D supplementation, especially in autumn and winter. Consume calcium-fortified plant milks and yogurts, calcium-set tofu, leafy greens, and sesame seeds.

Inadequate Protein and Calories

Some new vegans underestimate the need to replace the caloric and protein density of meat and dairy. Plant-based foods are often less calorie-dense, and relying on processed vegan junk food instead of nutrient-rich whole foods can lead to feeling lethargic. Protein is also vital for energy and tissue repair, and while it's plentiful in plants, ensuring enough variety and quantity is important.

The solution: Consciously increase portion sizes of staples like legumes, whole grains, nuts, and seeds to meet calorie needs. Incorporate protein-dense foods like tofu, tempeh, lentils, and seitan regularly. A balanced plate should feature a variety of food groups.

Digestive Adjustments and Underlying Issues

For some, the initial transition to a high-fiber vegan diet can cause digestive discomfort. Increased intake of legumes, whole grains, and vegetables can lead to bloating, gas, and temporary changes in bowel habits as your gut microbiome adjusts. In other cases, underlying conditions can be exacerbated.

High Fiber and Pre-existing IBS

While beneficial for most, the high fiber content of many vegan foods can worsen symptoms for individuals with Irritable Bowel Syndrome (IBS) or other digestive sensitivities.

The solution: A low-FODMAP diet, which reduces fermentable carbohydrates, can help manage symptoms while still being vegan. Working with a registered dietitian is advised.

Table: Poorly Planned vs. Well-Planned Vegan Diet


Feature	Poorly Planned Vegan Diet	Well-Planned Vegan Diet
Energy	Low, resulting in fatigue	High, with sustained energy
Nutrient Intake	Deficient in B12, Iron, D, Omega-3	Optimized through supplementation and fortified foods
Diet Focus	Processed vegan junk food	Whole, nutrient-dense plant foods
Digestion	Possible bloating, gas, and irregularity	Healthy, regular digestion after an initial adjustment period
Mood	Potential for mood dips and low concentration	Stable mood and mental clarity
Long-term Health	Potential for long-term health risks	Associated with reduced risk of chronic diseases

Actionable Steps to Improve Your Vegan Diet

Track your intake: Temporarily tracking your food and calorie intake can help you understand if you're eating enough to meet your energy needs.
Diversify protein sources: Incorporate a variety of legumes (beans, lentils), soy products (tofu, tempeh), seitan, and quinoa to ensure a complete amino acid profile throughout the day.
Fortified foods and supplements: Make B12 supplementation a non-negotiable part of your routine. Use fortified plant milks and nutritional yeast, and consider algae-based omega-3 oil and Vitamin D supplements.
Focus on whole foods: Prioritize whole grains, fruits, vegetables, nuts, and seeds over processed alternatives to maximize nutrient intake and fiber.
Combine for absorption: Enhance iron absorption by pairing plant-based iron sources with Vitamin C-rich foods. This simple change can make a significant difference.

Conclusion: Thriving, not just Surviving

Feeling unwell on a vegan diet is not a universal experience but a sign that specific nutritional adjustments are needed. By identifying and addressing potential deficiencies in key nutrients like B12, iron, and omega-3s, and moving away from processed foods towards a varied whole-food diet, you can overcome common hurdles. A properly planned vegan diet, often supported by targeted supplementation, can be a path to vibrant health and sustained energy. It is important to approach your diet mindfully, listen to your body, and seek professional guidance from a registered dietitian or doctor if symptoms persist.

For more detailed information on protein needs, consult reliable resources like the Vegan Health website(https://veganhealth.org/protein/protein-part-2/).

Frequently Asked Questions

The most common reasons for feeling unwell on a vegan diet are nutrient deficiencies, particularly Vitamin B12, iron, and omega-3 fatty acids, and unintentionally consuming too few calories due to the lower caloric density of many plant foods.

Yes, absolutely. Vitamin B12 is not naturally present in reliable quantities in plant foods, so consistent supplementation or regular consumption of B12-fortified foods is essential to prevent deficiency and irreversible nerve damage.

Low energy often points to inadequate calorie intake or iron deficiency. Ensure you are eating enough food by focusing on calorie-dense whole plant foods. Pair iron-rich foods with sources of Vitamin C to improve absorption.

Yes, it is very common. The significant increase in dietary fiber can cause temporary bloating, gas, or changes in bowel habits as your gut microbiome adjusts. This often improves over time as your body adapts to the higher fiber intake.

Yes, you can get plenty of protein. Plant-based foods like legumes, tofu, tempeh, seitan, nuts, and seeds are excellent protein sources. It's more about ensuring a variety of protein sources throughout the day rather than strictly combining them at every meal.

While plant sources provide ALA omega-3, the conversion to the more crucial EPA and DHA is inefficient. An algae-based omega-3 supplement is highly recommended to ensure adequate levels for brain and heart health.

Focus on consuming a variety of whole plant foods, including fruits, vegetables, whole grains, and legumes. Pay attention to key nutrients like B12 (supplement), iron (pair with Vitamin C), and omega-3s (supplement). Ensure sufficient calorie intake and minimize processed vegan junk food.