In Oxford, the blood of 689 men was tested for vitamin B12. A third of them ate meat, a third were vegetarian, a third were vegan. Among the 226 meat eaters, one man was deficient. Among the 232 vegans, more than half were. The meat eaters did not have to think about it at all.
These were not careless eaters. A vegan diet takes thought, label reading and plenty of vegetables. They were eating well by every standard the healthy-eating poster sets, and half of them were short of a vitamin the nerves and the blood cannot work without.
That is the gap this article is about. "Eating well", as it is usually taught, means more plants and less meat, and on those terms eating well is not enough. Follow that advice all the way and you end up needing pills, and not only for the nutrients plants never had. Some of what the body needs is simply not in plants, some is there in a form it struggles to use, and much of the rest is there in smaller amounts, locked behind the plant's own defences. Go the other way, and eat the whole animal, and the list of pills gets very short. Possibly empty.
The list
When 141 papers comparing plant eaters with meat eaters were pooled, the shortfalls lined up. Vegetarians and vegans took in less of, and had lower levels of, vitamin B12, vitamin D, iron, zinc, iodine and calcium, and they ate less of the long-chain omega-3 fats, EPA and DHA. Vegans came out lowest of all for B12, calcium and iodine, with lower iodine levels and less dense bones.
Read that list again. It is the front of a multivitamin label. A diet that needs its own multivitamin is telling you something.
And only part of it is about foods plants lack. B12, ready-made vitamin A and the long omega-3s come from animals; plants carry a shorter omega-3, ALA, and leave the body to make the rest, a conversion that is limited and weakest of all for DHA. Iron, zinc and calcium are in plants, in smaller amounts and bound up with compounds that stop them being absorbed. Iodine depends on the soil, and most fruits and vegetables are poor sources of it. A plant diet ends up supplementing the vitamins plants do not have and the minerals they will not give up.
Vitamin D shows how far the pill aisle has to go. Plants carry almost none of it. 7 Surprising Sources of Vitamin D3 You Need to Know for Better Health has where the capsules come from: mushrooms left in sunlight make vitamin D2, the weaker cousin, most vitamin D3 starts as lanolin, the grease in sheep's wool, and the vegan version is made from lichen.
And some of what a plant diet lacks is not on the label at all. Creatine, the energy reserve muscles and the brain draw on, comes mostly from meat and fish. A mixed diet supplies about half of what the body uses and the liver and kidneys make the rest, and vegetarians carry less of it in their muscles. When 128 young women were given creatine or a dummy pill for five days, memory improved in the vegetarians, not in the meat eaters.
To be fair to the plants, the same review found the plant eaters ahead on fibre, folate, magnesium and vitamins C and E, which is what plants are made of. It also found shortfalls on every kind of diet, mixed diets with meat included. The difference is which gaps, and how easily food closes them.
The vitamin plants cannot make
B12 is made by bacteria. Animals collect it, from their food and from the microbes in their gut, and store it, much of it in the liver. That is why meat, fish, eggs and milk carry it and plants do not.
Liver was the cure before anyone knew the vitamin existed. Pernicious anaemia, a disease in which the body loses the ability to absorb B12, was often fatal until around 1926, when George Minot and William Murphy put their patients on a diet heavy in raw liver. The symptoms improved rapidly and the red blood cell counts rose. Raw liver is hard to eat in quantity, so by 1928 a liver extract 50 to 100 times stronger was being made, and in 1934 Minot and Murphy shared the Nobel Prize with George Whipple, whose dogs had shown the effect of liver first.
The molecule behind the cure turned out to be the most chemically complex of all the vitamins, built around a single atom of cobalt. It was purified from liver extracts and named vitamin B12, and in 1964 Dorothy Hodgkin won the Nobel Prize in Chemistry, in part for working out its structure.
The body also keeps a reserve. The liver stores years' worth of B12, which is why a new vegan can feel perfectly well for years while the store quietly runs down. By the time the shortfall shows, the diet has long felt normal, and nothing seems to have changed.
Plant foods that claim it usually carry something else. When spirulina tablets were tested, most of what looked like B12 turned out to be a look-alike, pseudovitamin B12, which the human body cannot use. One standard lab test counted the look-alikes as B12 and read six to nine times higher than a second test did. So a vegan eating spirulina for B12 can look fine on the label and still run empty. Green, expensive, and mostly the wrong molecule.
Nutrient Deficiencies: Who's at Risk and Which Test to Get puts it plainly: anyone who eats no animal foods needs fortified foods or a supplement, and a breastfeeding mother on a vegan diet passes the shortfall to her baby. A vegan diet without a B12 pill is not a complete diet.
Even the endorsement comes with the pill. The German Nutrition Society holds, as of 2024, that a vegan diet can be healthy for adults when B12 is supplemented and the diet is planned so the critical nutrients are covered. For children, teenagers, older people and pregnant or breastfeeding women, it recommends neither for nor against, because the data is lacking.
Vitamin A that has to be built
Vitamin A comes in two shapes. Animal foods, liver above all, carry it ready to use, as retinol. Plants carry beta-carotene, the orange pigment in carrots, which the body has to convert into vitamin A first.
That conversion is less reliable than the carrot advertising suggests. Two common variants of the gene that does the converting cut the body's ability to turn beta-carotene into vitamin A, by 32% in women carrying one of them and by 69% in women carrying both. One of the variants turned up in 42% of the gene copies tested, the other in 24%. You cannot tell which kind of converter you are by looking in the mirror, and a plate full of orange vegetables will not tell you either.
What a Diet That Supports Your Health Looks Like has why retinol is the form worth eating. A slice of liver skips the conversion entirely, and your genes get no say.
Minerals plants keep to themselves
Plants guard their minerals. Grains, beans, nuts and seeds store phosphorus as phytic acid, which binds calcium, iron and zinc in the gut and stops much of them being absorbed. Spinach and other greens carry oxalate, which does the same to calcium. Why Your Fruits and Vegetables Deliver Less Than You Think, linked below, has how much gets locked away.
Iron shows the gap most clearly. Meat, fish and liver carry part of their iron as haem iron, the form the body absorbs best. Plants carry only the other kind, non-haem iron, which the body takes up less readily and which the blockers hold back further. So a bowl of lentils can carry plenty of iron on paper and deliver a fraction of it, and a plant eater can eat iron every day and still need the tablet. Iron on the label is not iron in the blood.
Zinc follows the same pattern. Across 26 comparisons pooled together, vegetarians took in less zinc and had less of it in their blood than meat eaters, and the gap was wider in women and in vegans.
Iodine and bones
Two more gaps show up when the animal foods go.
Iodine runs the thyroid, and it comes mostly from fish, shellfish, eggs and milk. A review of 15 papers covering 127,094 adults found that vegans had the lowest iodine levels of any group, short of optimal. The few vegans with very high intakes got there through seaweed, which can carry so much iodine that it swings people from too little to too much. It is the only iodine source that comes with a lottery.
Salt is no rescue either. Good unrefined salt earns its place on the plate for other reasons, but Nutrient Deficiencies has the catch: sea salt and pink salt carry little iodine.
Bones are the slower story. In the same Oxford project, 54,898 people were followed for 17.6 years on average. Compared with meat eaters, vegans had 2.3 times the risk of a hip fracture: about 15 more broken hips for every thousand people over ten years. Fish eaters and vegetarians sat in between. The gap shrank a little, but held, when the figures were adjusted for calcium and protein, so it is not simply a matter of drinking more fortified milk.
Plants are getting poorer
Even the plants that do carry minerals carry fewer of them than they used to.
The longest record we have comes from a single wheat field. The Broadbalk experiment at Rothamsted, in England, has grown wheat on the same ground since 1843, and samples of the grain and the soil have been kept in an archive for most of that time. When the grain was tested, its zinc, iron, copper and magnesium held steady from 1845 to the mid-1960s. Then they fell, at the point when the new semi-dwarf, high-yield varieties arrived.
The soil was not to blame. Its minerals stayed level or rose. The fertiliser was not to blame either: the same fall showed up in the plots that got no fertiliser, mineral fertiliser and farmyard manure. What changed was the plant. Breeders selected for bigger harvests, nobody intended the minerals to drop, and the extra bulk simply diluted them. Why Your Fruits and Vegetables Deliver Less Than You Think has the same pattern in 43 garden crops: six nutrients lower in 1999 than in 1950, by between 6% and 38%.
And the most famous vegetable claim of all was never quite what it seemed. Popeye's strength is usually put down to the iron in spinach. In a 1932 strip, Popeye says "spinach is full of vitamin A", and spinach is no better a source of iron than many other vegetables. The iron legend stuck harder than the facts. The cartoon was more accurate than the myth about it.
What drains the rest
Getting a nutrient into your mouth and getting it into your blood are two separate things, and the body can lose ground on the way. Why Your Mineral Supplements Keep Canceling Each Other Out, linked below, has the medicines that drain minerals and vitamins, and why piling on pills makes the competition worse. Why Most Stress Supplements Fail (And the 9 Worth a Look) has the vicious circle between stress and magnesium: stress may increase the loss of magnesium, and a shortage may make the body react more strongly to stress. And Why "Drink More Water" Is Incomplete Advice has the water filter's share: reverse osmosis removes most contaminants, and most of the minerals with them.
Put it together, and a careful eater who still feels flat is facing a structural problem, not a personal failing. Nourishment is a system with several points of failure, and a plant-heavy plate fails at more of them.
Nose to tail
Animal foods sidestep most of this. An animal has already done the collecting: it grazed, it concentrated what it ate, and it stored the minerals and vitamins in its muscle, its organs and its bones. There is no phytic acid in a steak and no oxalate in an egg. Nobody has ever had to soak a steak overnight. Part of the iron is haem iron, the vitamin A is ready-made, and the B12 is real.
How the animal lived still matters. A review of three decades of measurements found that grass-fed beef carries more omega-3 fats, more CLA and more of the building blocks of vitamins A and E than grain-fed beef. Eggs from hens on pasture, compared with caged hens on commercial feed, had twice the vitamin E, twice the long-chain omega-3 and two and a half times the total omega-3. Wild fish, pastured eggs and grass-fed meat are the versions worth paying for.
And "nose to tail" means the whole animal, not just the steak. Liver carries vitamin A, folate, B12, iron and copper in one serving. Oysters and other shellfish lead everything for zinc and bring iodine and selenium. Small fish eaten with their bones bring calcium, and a tin of keeps in the cupboard. Bone broth, skin and slow-cooked cuts bring what lean muscle leaves out. For the case at length, there is Paul Saladino's , a guide to nose-to-tail eating. For the cooking, there is Fergus Henderson's , which makes offal taste like dinner rather than a dare. Processed meat is not the same thing: a hot dog is a meat product, not a nose-to-tail meal.
Does it work in practice? The explorer Vilhjalmur Stefansson lived on meat and fish in the Arctic, raw seal liver included, and in the late 1920s he and a companion ate nothing but meat for a year under hospital checks, which is more supervision than most diets ever get. 8 Smart Ways to Fight Cognitive Decline with Food has what they found: no ill effects. A century later, 2,029 adults who had eaten a carnivore diet for six months or more, a median of 14 months, answered a detailed survey. 85% ate red meat every day, fewer than one in ten ate vegetables more than once a month, and 37% took no vitamin supplements at all. Adverse symptoms were rare, and they reported benefits and high satisfaction.
The honest gaps
That survey has limits worth saying out loud. The answers were self-reported, the people who answered were, by definition, the ones still on the diet, those who reported their cholesterol had high LDL, and nobody has yet followed carnivore eaters for decades.
The other check is arithmetic. When four carnivore meal plans were modelled against the official reference values, they met riboflavin, niacin, phosphorus, zinc, B6, B12, selenium and vitamin A. They fell short on paper for thiamin, magnesium, calcium and vitamin C, and in some plans iron, folate, iodine and potassium.
Most of those gaps close with the parts of the animal the plans left thin. Liver brings folate and iron. Fish, shellfish and eggs bring iodine. Bones you eat bring calcium. Pork brings thiamin. Vitamin C is the one that surprises: when 37 traditional Inuit foods were tested, raw fish roe, raw whale skin, and caribou and seal liver all turned out to be rich sources, which is where a diet with almost no plants found it. Magnesium is the gap with the least obvious fix, and the one worth testing rather than guessing.
There is also a question the reference values cannot answer. They were worked out on people eating mixed diets, and the authors of the meal-plan model say it is still undetermined whether a carnivore metabolism needs less of some nutrients. Whether figures built on ordinary mixed diets fit a diet with no sugar, no grains and no plant blockers is an open question, not a settled one.
When to check anyway
Nose to tail covers what food can cover. It cannot cover what a medicine takes away. Acid blockers and metformin both drain B12, and Why Your Mineral Supplements Keep Canceling Each Other Out has the figures. Neither is a reason to stop a prescribed medicine on your own. Both are reasons to get checked, whatever you eat.
Nutrient Deficiencies has who is most at risk and which test answers which question. A blood test settles what years of guessing cannot. If the number comes back low on a nose-to-tail diet, look first at which part of the animal is missing from the plate.
Eating the whole animal
The Oxford vegans were eating well by the poster's definition, and half of them were short of B12. That is not a failure of willpower. It is what happens when "eating well" means eating around the foods that carry what the body needs.
Eating well still matters. It just needs a new definition: the whole animal, raised well, with plants as the side, not the foundation. On that plate, the supplement shelf has very little left to sell you.
The organ that cured a fatal B12 disease before the vitamin had a name is still the best place to start. This week, put liver on the plate once.
Still filling half the plate with vegetables? Why Your Fruits and Vegetables Deliver Less Than You Think — how much less our crops hold than in 1950 and why bigger can mean thinner, why frozen can beat fresh, the beans that are poisonous raw, why more antioxidants is not the win it sounds, and the foods that deliver without the catch.
Already taking a handful of supplements? Why Your Mineral Supplements Keep Canceling Each Other Out — why pills compete where food does not, the hormone that shuts the iron door, the protein that traps copper, the foods that carry minerals without the fight, and the medicines that drain them.
Know someone who takes a fistful of pills with their salad? Send them this, and a slice of liver.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional, especially if you eat a vegan or vegetarian diet, are pregnant or breastfeeding (liver is best left out in pregnancy because of its vitamin A), are planning a big change to what you eat, or take prescribed medicines. Do not stop a prescribed medicine without advice.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
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