A vegan diet eliminates all animal products, and while it can be healthful with careful planning, it introduces real nutritional gaps, practical challenges, and biological trade-offs that are worth understanding before you commit. These aren’t theoretical concerns. They show up in blood work, bone density scans, and the lived experience of the 84% of people who eventually return to eating animal products after trying a vegetarian or vegan diet.
Vitamin B12 Is Nearly Absent From Plant Foods
The single most well-established nutritional risk of veganism is vitamin B12 deficiency. Vegans get roughly 0.43 micrograms of B12 per day from food alone, compared to about 2.14 micrograms for omnivores. That’s a fraction of the recommended 2.4 micrograms daily. B12 is essential for nerve function, DNA synthesis, and red blood cell production. Without it, you risk irreversible nerve damage, memory problems, and a type of anemia that causes deep fatigue.
The good news is that supplementation works. In one study of young, health-conscious vegans, about 90% were taking B12 supplements (with a median dose of 250 micrograms per day), and their blood levels looked fine. But that finding actually underscores the point: a vegan diet cannot meet this basic need on its own. You’re dependent on a supplement for a nutrient that omnivores get effortlessly from food. If you forget, run out, or absorb poorly (which becomes more common with age), the consequences are serious.
Plant Protein Is Less Complete and Harder to Use
Not all protein is created equal. Scientists measure protein quality using a score called DIAAS, which accounts for how well your body can actually digest and use the amino acids in a food. Pork, egg, and casein (from dairy) all score above 100, meaning excellent quality. Whey protein and soy score 85 and 91 respectively, both considered high quality. But most other plant proteins fall short: pea protein scores around 70, rice protein 47, corn protein 36, and wheat protein 48. These low scores reflect a shortage of specific amino acids, particularly lysine, that your body can’t make on its own.
You can combine plant proteins to cover each other’s gaps (rice and beans, for example), but this requires consistent planning. For older adults trying to preserve muscle mass, or athletes trying to build it, the lower digestibility of plant proteins means you need to eat significantly more total protein to get the same functional benefit.
Your Body Struggles to Make Its Own Omega-3s
The omega-3 fats that matter most for your brain and heart are EPA and DHA, found primarily in fatty fish and seafood. Plants provide a precursor called ALA (from flaxseed, chia, and walnuts), but your body is remarkably inefficient at converting it. In men, only about 8% of ALA converts to EPA and somewhere between 0% and 4% converts to DHA. Women do somewhat better, converting roughly 21% to EPA and 9% to DHA, likely due to the influence of estrogen.
DHA is a structural component of your brain and retina. These conversion rates are low enough that some researchers consider EPA and DHA “conditionally essential” nutrients, meaning your body technically makes them but not in amounts that reliably meet your needs. Algae-based DHA supplements exist, but again, you’re adding another supplement to compensate for what the diet can’t provide.
Iron and Mineral Absorption Are Reduced
Plants contain iron, but it’s a different form than what’s in meat. Heme iron from animal foods is absorbed at about 15%, while non-heme iron from plants is absorbed at roughly 7%. That’s half the efficiency. You can improve plant iron absorption by pairing it with vitamin C, but you’re still working harder for less.
Compounds naturally present in many plant foods make this worse. Phytates, found in grains, legumes, nuts, and seeds, bind tightly to iron, calcium, and zinc, forming complexes your body can’t break down. Oxalates in spinach, beets, and sweet potatoes do the same thing with calcium, iron, and magnesium. This doesn’t mean these foods are unhealthy, but it does mean the mineral content listed on a nutrition label overstates what your body actually absorbs. For vegans relying entirely on these foods for minerals like calcium and zinc, the real intake can fall meaningfully short of what the numbers suggest.
Higher Fracture Risk Is Documented
The EPIC-Oxford study, one of the largest long-term studies comparing dietary groups, found that vegans had a 43% higher risk of fractures overall compared to meat eaters. For hip fractures specifically, the risk was 131% higher. That’s after adjusting for lifestyle factors and body weight.
Part of this is likely explained by lower calcium intake, compounded by the absorption issues described above. Lower body weight in vegans may also play a role, since carrying less weight means less mechanical loading on bones. Regardless of the mechanism, these are large differences in a health outcome that becomes increasingly important with age. Hip fractures in older adults carry serious risks of disability and loss of independence.
Creatine and Brain Performance
Creatine is found almost exclusively in meat and fish, and vegetarians are known to have lower muscle creatine stores than omnivores. Your brain also uses creatine for energy, particularly during demanding cognitive tasks. In a study comparing the effects of creatine supplementation on vegetarians and omnivores, vegetarians showed improved memory after supplementing, while omnivores did not. This suggests vegetarians (and by extension vegans) start from a lower baseline of brain creatine that limits their cognitive performance in certain areas.
Your body does produce some creatine on its own, so this isn’t a crisis. But it’s another example of a compound that omnivores get abundantly from food while vegans operate at a subtle disadvantage unless they supplement.
The Mental Health Picture Is Unclear
If you’ve seen headlines linking veganism to depression, the reality is more nuanced but still worth taking seriously. A systematic review and meta-analysis found that following a vegan or vegetarian diet was associated with a higher risk of depression, though lower anxiety scores. One observational study found that people adhering to a vegetarian diet were 53% more likely to experience depression than omnivores. However, intervention studies (where researchers assigned people to follow a vegan diet) have found reduced stress and improved depression indicators after 18 weeks.
The contradiction likely comes down to what people actually eat. Studies that separate “healthy” plant-based diets (whole grains, fruits, vegetables, legumes) from “unhealthy” ones (refined grains, sugary drinks, processed snacks) consistently find that healthy versions are linked to better mental health, while the unhealthy versions are linked to worse outcomes. Going vegan doesn’t automatically mean eating well, and someone living on pasta, chips, and processed vegan foods may feel worse for reasons that have nothing to do with the absence of meat specifically.
Nutritional deficiencies themselves can also drive mood changes. Low B12, low omega-3s, and low iron all have documented effects on brain chemistry and energy levels.
Pregnancy and Child Development Require Extra Caution
Several nutrients critical for fetal brain development are either absent or poorly supplied by vegan diets: B12, iodine, iron, and long-chain omega-3 fats. B12 deficiency during pregnancy has been linked to lower cognitive scores in children at age two, an effect worsened when other B vitamins are also low. Iodine deficiency, even at marginal levels, may impair fetal brain development. Emerging research connects a mother’s preconception iodine status to her child’s IQ at ages six to seven.
This doesn’t mean vegan pregnancies inevitably produce poor outcomes. It means the margin for error is much thinner. Careful supplementation and monitoring can bridge the gaps, but the stakes are high enough that this period of life demands particular attention if you’re eating entirely plant-based.
Most People Who Try Veganism Quit
A large survey by the research organization Faunalytics asked former vegetarians and vegans why they stopped. Among 908 respondents, 32% said they were unsatisfied with the food, 26% cited health concerns, 13% pointed to social difficulties, and another 13% found it too inconvenient. Cost and lack of motivation each accounted for 6%.
These numbers reflect the lived reality of restricting an entire category of food. Eating out becomes harder. Social gatherings require negotiation or advance planning. Travel in many parts of the world means limited options. Over time, these frictions wear people down, especially when the dietary choice was motivated more by curiosity than deep conviction. The social and practical costs of veganism are often underestimated by people who haven’t tried it yet.
Muscle Maintenance as You Age
Sarcopenia, the age-related loss of muscle mass and strength, is a major concern for adults over 65. The relationship between plant-based diets and sarcopenia depends heavily on food quality. In a case-control study of older adults, those who followed an “unhealthy” plant-based diet (heavy in refined grains and processed foods) had nearly 3.7 times the odds of sarcopenia compared to those with lower adherence. But those following a healthy, whole-food plant-based diet actually had lower odds of sarcopenia than people eating poorly overall.
The takeaway isn’t that plant-based eating causes muscle loss. It’s that meeting protein needs from plants alone requires deliberate effort, and the quality of those choices matters enormously. Older adults need more protein per meal to stimulate muscle maintenance, and the lower digestibility of most plant proteins makes this a real logistical challenge for vegans who aren’t paying close attention.
Soy and Thyroid Function
Since vegans often rely heavily on soy for protein, concerns about soy’s effect on thyroid function come up frequently. Soy isoflavones can inhibit an enzyme involved in thyroid hormone production in lab settings, but the majority of human studies have found no significant effect of soy on thyroid function in healthy adults. Research in primates suggests soy may even help preserve thyroid hormone levels after menopause. The key caveat: if you have an existing thyroid condition or low iodine intake (already a risk on vegan diets), high soy consumption could compound the problem. For most people with adequate iodine, soy appears to be fine.