According to Gram Research analysis, vegans have significantly lower levels of omega-3 fatty acids, vitamin D, and iodine compared to vegetarians and meat-eaters. A 2026 cross-sectional study of 115 Taiwanese adults found that 75% of vegans had vitamin D deficiency, compared to 36% of meat-eaters, and vegans’ omega-3 index was 2.6 versus 5.8 for meat-eaters. While vegan diets excel at reducing unhealthy saturated fats, vegans may need supplements or fortified foods to meet their needs for these three critical nutrients.
A new study of Taiwanese adults compared the nutrition levels of vegans, vegetarians, and meat-eaters. Researchers found that vegans had lower levels of omega-3 fatty acids, vitamin D, and iodine in their blood and urine. While vegan diets were better at keeping saturated fat levels low, three out of four vegans showed signs of vitamin D deficiency, and most didn’t get enough iodine. The findings suggest that people following vegan diets may need to pay special attention to getting these specific nutrients through supplements or fortified foods.
Key Statistics
A 2026 cross-sectional study of 115 Taiwanese adults found that 75% of vegans had vitamin D deficiency, compared to just 36% of meat-eaters and 24% of vegetarians.
Vegans in the study had an omega-3 index of 2.6, significantly lower than vegetarians at 3.7 and meat-eaters at 5.8, indicating substantially lower omega-3 fatty acid levels in their blood.
Iodine insufficiency affected 76% of vegans in the study, compared to 57% of vegetarians and 56% of meat-eaters, highlighting a widespread nutritional gap in plant-based diets.
Vegans had the lowest levels of saturated fat and trans-fat among all three diet groups, demonstrating that vegan diets naturally support heart health by reducing unhealthy fats.
The Quick Take
- What they studied: Whether vegans, vegetarians, and meat-eaters have different levels of important nutrients in their blood, specifically omega-3 fatty acids, vitamin D, and iodine.
- Who participated: 115 adults living in Taiwan: 45 meat-eaters, 46 people who eat dairy and eggs but no meat, and 24 vegans who eat no animal products at all.
- Key finding: Vegans had much lower omega-3 levels (2.6 on the omega-3 index) compared to vegetarians (3.7) and meat-eaters (5.8). Three-quarters of vegans had vitamin D deficiency, compared to just one-third of meat-eaters.
- What it means for you: If you’re vegan, you may want to talk to a doctor about taking vitamin D and omega-3 supplements, or eating more fortified foods. This doesn’t mean veganism is unhealthy—it just means being intentional about certain nutrients.
The Research Details
Researchers recruited 115 adults in Taiwan and divided them into three groups based on their diet: those who eat meat, those who eat dairy and eggs but not meat, and those who eat no animal products. Everyone gave blood samples and urine samples on the same day. The researchers then measured specific nutrients in these samples, including omega-3 fatty acids (measured in red blood cells), vitamin D (measured in blood plasma), and iodine (measured in urine).
This type of study is called ‘cross-sectional,’ which means researchers took a snapshot of everyone at one point in time rather than following them over months or years. It’s like taking a photo instead of making a video. This approach is quick and affordable but can’t prove that diet causes the differences—only that the differences exist.
This research matters because veganism is becoming more popular for environmental and ethical reasons, but people need to know if it’s nutritionally complete. By measuring actual nutrient levels in the blood and urine rather than just asking people what they eat, the researchers got accurate information about what’s really happening in people’s bodies.
The study is reliable in what it measures—the blood and urine tests are accurate ways to check nutrient levels. However, the sample size is relatively small (115 people), and all participants were from Taiwan, so results might be different in other countries with different food availability. The study shows associations but cannot prove that veganism causes the nutrient deficiencies, since people’s overall eating habits and supplement use weren’t fully controlled.
What the Results Show
Vegans had significantly lower omega-3 fatty acid levels than both vegetarians and meat-eaters. The omega-3 index—a measure of how much omega-3 is in your red blood cells—was 2.6 for vegans, 3.7 for vegetarians, and 5.8 for meat-eaters. This matters because omega-3s are important for heart and brain health.
Vitamin D deficiency was the most striking finding. Among vegans, 75% had vitamin D deficiency, compared to 36% of meat-eaters and 24% of vegetarians. Vitamin D is crucial for bone health and immune function. The difference is likely because vitamin D is naturally found mainly in animal products like fatty fish and egg yolks, and fortified plant-based milk isn’t always available or consumed regularly.
Iodine insufficiency was also more common in vegans (76%) than in vegetarians (57%) and meat-eaters (56%). Iodine is essential for thyroid function. Seaweed is a plant-based source of iodine, but the amount varies widely, making it an unreliable source.
One positive finding: vegans had the lowest levels of saturated fat and trans-fat, which are linked to heart disease. This suggests that vegan diets naturally support heart health in this way.
The study found that vegans had higher omega-6 fatty acid levels than the other groups. While omega-6 is necessary, the ratio of omega-3 to omega-6 matters for health. Vegans’ higher omega-6 and lower omega-3 created an imbalanced ratio, which may increase inflammation in the body.
These findings align with previous research showing that plant-based diets can be lower in certain nutrients. However, this is one of the first studies to directly measure these nutrients in the blood and urine of Taiwanese vegans, vegetarians, and meat-eaters together. The vitamin D deficiency rates are particularly striking and higher than some previous studies, possibly because Taiwan has less sun exposure in winter and fortified foods are less common.
The study only included 115 people from Taiwan, so results may not apply to vegans in other countries with different climates, food availability, or supplement use. The study didn’t ask detailed questions about supplements people were taking, which could have affected the results. Because it’s a snapshot in time, we can’t know if these nutrient levels stay the same or change over time. Finally, the study can’t prove that veganism causes these deficiencies—only that vegans in this study had lower levels.
The Bottom Line
If you follow a vegan diet, consider: (1) Taking a vitamin D supplement, especially if you live in a place with limited winter sunlight—this is a high-confidence recommendation based on the 75% deficiency rate; (2) Taking an algae-based omega-3 supplement or eating algae products regularly—moderate confidence; (3) Using iodized salt or taking an iodine supplement—moderate confidence; (4) Eating fortified plant-based foods when available. Talk to your doctor or a registered dietitian about which supplements make sense for you.
This research is most relevant to people following or considering a vegan diet. Vegetarians who eat dairy and eggs appear to have better nutrient status, especially for vitamin D and iodine. Meat-eaters don’t need to make changes based on this research. Vegans living in sunny climates or those already taking supplements may have different results than this study showed.
Vitamin D deficiency takes months to develop and months to correct, so if you start supplementing, expect to see improvements in blood tests after 2-3 months. Omega-3 levels in red blood cells take 3-4 months to change. Iodine status can improve more quickly, within weeks, if you add iodized salt or supplements.
Frequently Asked Questions
Do vegans need to take supplements for vitamin D and omega-3?
Research shows that most vegans have low levels of these nutrients. A 2026 study found 75% of vegans had vitamin D deficiency. Supplements or fortified foods are recommended, though individual needs vary. Consult your doctor about what’s right for you.
Is a vegan diet nutritionally complete?
Vegan diets can be healthy but require careful planning for certain nutrients. This study shows vegans had excellent saturated fat levels but needed attention to omega-3s, vitamin D, and iodine. With proper supplementation or fortified foods, vegan diets can be complete.
What plant-based foods have omega-3 fatty acids?
Plant sources include flaxseeds, chia seeds, walnuts, and hemp seeds, but they contain ALA omega-3, not the EPA and DHA found in fish. Algae supplements provide EPA and DHA directly and are the most effective plant-based option for vegans.
How can vegans get enough iodine without eating fish?
Use iodized salt in cooking, eat seaweed occasionally (though amounts vary), or take an iodine supplement. A 2026 study found 76% of vegans had iodine insufficiency, making supplementation or consistent use of iodized salt important.
Are vegetarians who eat dairy and eggs healthier than vegans?
This study found vegetarians had better vitamin D and iodine status than vegans, likely because dairy and eggs contain these nutrients. However, both groups need to monitor these nutrients. Individual health depends on many factors beyond diet type.
Want to Apply This Research?
- Log daily supplement intake (vitamin D, omega-3, iodine) and weekly consumption of fortified foods. Set reminders for supplement timing and track any symptoms of deficiency like fatigue or dry skin.
- Add one new plant-based omega-3 source this week (algae supplement, ground flaxseed, or chia seeds). Next week, switch to iodized salt if you haven’t already. The following week, start a vitamin D supplement or increase sun exposure by 15 minutes daily.
- Check in monthly on supplement adherence. Schedule annual blood tests to measure vitamin D and omega-3 levels. Use the app to track energy levels and mood, which may improve as nutrient status improves.
This research describes nutritional differences between diet types but does not constitute medical advice. Individual nutritional needs vary based on age, health status, medications, and other factors. Before starting supplements or making significant dietary changes, consult with a healthcare provider or registered dietitian. This study was conducted in Taiwan and may not apply to all populations. If you have symptoms of nutrient deficiency (fatigue, bone pain, thyroid issues), seek medical evaluation rather than self-treating.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.