Why don't I feel good on a vegan diet? Your comprehensive guide

October 29, 2025 •

5 min read

An estimated half of all vegans are deficient in vitamin B12, a crucial nutrient for energy production and nerve health. If you're wondering, why don't I feel good on a vegan diet?, it's often due to easily fixable issues, not the diet itself being inherently flawed.

Quick Summary

This guide explores common issues such as nutrient deficiencies, insufficient calorie intake, and relying on processed foods that may cause feelings of fatigue and poor health on a vegan diet. Learn how proper planning and supplementation can help you thrive.

Key Points

B12 is essential for vegans: Vitamin B12 is not reliably found in plant foods, making consistent supplementation or consumption of fortified foods non-negotiable for preventing deficiencies.
Calorie intake is often underestimated: Plant-based foods are less calorie-dense, so many new vegans accidentally under-eat, leading to fatigue and low energy.
Nutrient absorption requires strategy: Non-heme iron from plants needs vitamin C for better absorption, while Omega-3 conversion is inefficient, often requiring an algae-based supplement.
Avoid the 'junk food vegan' trap: A diet heavy in processed vegan foods, rather than whole plant foods, can be just as unhealthy and nutritionally deficient as any other junk food diet.
Consult a professional for persistent issues: If you continue to feel unwell despite proper planning, consult a healthcare provider for blood tests to identify specific deficiencies.

Adopting a vegan lifestyle can offer numerous health benefits, such as a lower risk of heart disease and reduced cholesterol. However, some people transitioning to a plant-based diet report feeling unwell, experiencing fatigue, or having low energy. These issues are typically not a flaw of the diet itself but rather the result of a poorly planned approach. By understanding the common pitfalls and how to correct them, you can ensure your vegan diet supports your health and well-being.

The usual suspects: Key nutrient deficiencies

While a whole-food, plant-based diet is rich in many vitamins and minerals, certain nutrients are less bioavailable or naturally scarce in plant foods. Being mindful of these is crucial for long-term health.

Vitamin B12: The non-negotiable supplement

Vitamin B12 is produced by bacteria and is found naturally in animal products, but not reliably in plant foods. Deficiencies can lead to severe issues like anemia, fatigue, nerve damage, and memory problems. The Vegan Society recommends that all vegans either eat B12-fortified foods daily or take a supplement. This is one of the most critical aspects of a healthy vegan diet.

Iron: Understanding the non-heme difference

Plant-based diets contain non-heme iron, which is less readily absorbed by the body than the heme iron found in meat. However, adequate iron is achievable with planning. Combining iron-rich plant foods with vitamin C-rich foods significantly boosts absorption. It is also wise to avoid drinking tea or coffee with high-iron meals, as they contain compounds that inhibit absorption. Good plant-based iron sources include lentils, beans, tofu, whole grains, and leafy greens.

Omega-3 Fatty Acids: Ensuring adequate EPA and DHA

While plant sources like flaxseeds, chia seeds, and walnuts provide alpha-linolenic acid (ALA), the body's conversion of ALA into the crucial long-chain omega-3s, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), is often inefficient. To ensure optimal brain and heart health, many vegans supplement with an algae-based source of DHA and EPA.

Calcium, Zinc, and Iodine: Planning for minerals

Dairy products are a major source of calcium in omnivorous diets, making it a potential concern for vegans. However, many plant-based foods, including fortified plant milks, tofu, and leafy greens, are good sources. Similarly, zinc from plant sources is less bioavailable due to phytates, suggesting vegans may need a higher intake or supplementation. Iodine is also often lacking and can be obtained from iodized salt or supplements, avoiding reliance on inconsistent seaweed sources.

Common dietary mistakes to avoid

Simply removing animal products does not guarantee a healthy diet. Many newcomers make common mistakes that sabotage their well-being.

Not eating enough calories

Plant foods are typically lower in energy density than animal products. This means you need to eat a larger volume of food to meet your energy needs. If you feel tired or lethargic, it may be due to a simple calorie deficit. Including more calorie-dense plant foods like nuts, seeds, avocados, and whole grains can help.

Relying on processed 'junk' foods

The market for vegan processed foods is booming, but relying on meat substitutes, vegan cheeses, and sugary treats can result in a nutrient-poor diet. Just like an omnivore diet can be unhealthy with too much junk food, a vegan diet filled with processed items will leave you short on essential nutrients and energy. Focus on whole, unprocessed plant foods to maximize nutrition.

Ignoring proper protein intake

While protein deficiency is rare for vegans eating enough calories and a varied diet, some individuals, especially those with higher activity levels, may benefit from paying closer attention to protein sources. Consuming a variety of legumes, soy products, nuts, seeds, and whole grains throughout the day ensures all essential amino acids are acquired.

Making the transition: From struggle to success

Comparing a poorly-planned versus a well-planned vegan diet


Feature	Poorly-Planned Vegan Diet	Well-Planned Vegan Diet
Symptom Profile	Fatigue, weakness, brain fog, anemia risk, poor skin/hair health, mood issues.	High energy, vitality, strong immune system, reduced risk of chronic diseases.
Typical Meal Composition	Often centered on pasta, white bread, processed vegan meats and cheeses, chips.	Diverse and whole-food based: includes legumes, vegetables, whole grains, fruits, nuts, seeds.
Calorie Intake	Often insufficient due to low energy density of some plant foods, leading to lethargy.	Consciously includes calorie-dense foods like nuts, avocados, and seeds to meet energy needs.
Key Supplements	Often neglected, leading to deficiencies, especially B12.	Consistently includes B12, and often vitamin D, iodine, and algae-based omega-3s.
Protein Strategy	Not tracking protein sources, potentially leading to lower overall intake.	Incorporates a variety of protein sources like lentils, tofu, beans, and seeds at each meal.
Key Nutrient Focus	Overlooks less bioavailable nutrients like iron, zinc, and DHA/EPA.	Strategic food pairing (e.g., Vitamin C with iron) and supplementation to optimize nutrient intake.

Steps to take if you feel unwell

Evaluate your caloric intake: Track your food for a few days to ensure you are eating enough. If switching from a calorically dense omnivore diet, you may need to increase your food volume significantly.
Prioritize B12 supplementation: Ensure you are consistently taking a reliable B12 supplement. This is non-negotiable for all vegans.
Get blood tests: If symptoms persist, consult a doctor and request blood tests for B12, iron, ferritin, vitamin D, and zinc. This can help pinpoint specific deficiencies.
Focus on whole foods: Center your diet around whole grains, legumes, vegetables, fruits, nuts, and seeds. Limit processed alternatives.
Optimize nutrient absorption: Pair iron-rich foods with vitamin C and consider an algae-based omega-3 supplement to address EPA and DHA needs.
Be patient with the transition: Your gut microbiome will change in response to a higher fiber diet, and it may take time for your body to fully adapt.

Conclusion: The power of a well-planned plate

If you find yourself asking, why don't I feel good on a vegan diet?, the answer is almost always rooted in inadequate planning rather than a flaw with veganism itself. By consciously addressing potential nutrient gaps, monitoring your calorie intake, and prioritizing whole foods over processed alternatives, you can overcome initial hurdles. Remember, a thriving vegan lifestyle is built on a diverse, well-thought-out, and balanced nutritional foundation, not just the absence of animal products. For further resources and specific nutritional guidance, consult The Vegan Society's nutrition resources.

Frequently Asked Questions

Yes, some initial fatigue can occur for several reasons, including a temporary calorie deficit from not adjusting to the lower energy density of plant foods, or your body adapting to a high-fiber intake. Ensuring you eat enough overall calories and nutrient-dense foods can help.

Vegans must obtain Vitamin B12 from supplements or fortified foods, such as plant milks, nutritional yeast, and cereals, because it is not reliably present in plant foods.

To increase iron absorption, pair iron-rich plant foods like lentils and spinach with a good source of Vitamin C, such as citrus fruits or bell peppers. Additionally, avoid drinking coffee or tea within an hour of your meal.

Protein deficiency is uncommon in vegans who consume a varied and calorically sufficient diet. A diverse intake of legumes, whole grains, nuts, and seeds provides all the necessary amino acids.

No, just because a food is vegan doesn't mean it's healthy. Many processed foods like cookies, chips, and meat substitutes are vegan but lack the nutrients of whole plant foods and can be high in salt, sugar, and unhealthy fats.

While plant foods provide ALA, the body's conversion to EPA and DHA is inefficient. Many vegans choose to take an algae-based supplement to ensure adequate intake of these crucial fatty acids.

If your symptoms, such as persistent fatigue or brain fog, do not improve with dietary adjustments, it's recommended to consult a doctor. They can order blood tests to check for specific deficiencies like B12, iron, and vitamin D and rule out other underlying health issues.