Are plant-based diets healthier?

Well-constructed ones are, with consistent evidence from large cohorts for lower cholesterol, blood pressure, type 2 diabetes and heart disease. But the qualifier is doing real work. Studies that separate healthful plant foods — whole grains, vegetables, fruit, nuts, legumes — from less healthful ones — refined grains, sugary drinks, sweets, chips — find that only the first pattern lowers risk, while a plant-based diet built from the second raises it. A vegan diet of white bread, crisps, soft drinks and processed meat analogues carries the ultra-processed food risk profile like any other. So the useful question is not whether animal foods have been removed but what has replaced them, and the food industry has been quick to attach the plant-based label to products that meet the definition and help nobody.

Do I really need to take B12?

Yes, if you are vegan, and this is one of the few genuinely non-negotiable points in nutrition. B12 is made by bacteria, not plants, and no unfortified plant food is a reliable source. Spirulina and some seaweeds contain pseudo-B12 analogues that are biologically inactive and can even interfere with the blood test, giving false reassurance. Deficiency causes anaemia and, more seriously, degeneration of the spinal cord that becomes irreversible if it continues long enough. There is a particular trap: plant-based diets are high in folate, and folate corrects the anaemia while the nerve damage continues silently — so a normal blood count does not exclude deficiency. Take a supplement or use reliably fortified foods, and if there is any doubt, methylmalonic acid is a better test than serum B12.

What else needs attention besides B12?

Iodine is the most neglected, and in some ways the most consequential. Dairy is a major iodine source in many countries, and most plant milks are not fortified with it even when they are fortified with calcium and B12. Iodine deficiency in pregnancy causes irreversible harm to fetal brain development, and seaweed is an unreliable substitute because content varies enormously and kelp can supply a dangerous excess. Iron and zinc from plants are less well absorbed, though this improves substantially if you take vitamin C with meals and keep tea and coffee between meals rather than with them. Omega-3 conversion from flax and walnuts to the long-chain forms is inefficient, so algal oil is worth considering, particularly in pregnancy. Vitamin D and calcium need attention where fortified products are not used consistently.

Is it safe for children and in pregnancy?

Yes, when properly planned — major dietetic bodies state that well-planned vegetarian and vegan diets are appropriate at all life stages — but these are the situations with the least margin for error, and specialist dietetic input is genuinely worthwhile rather than a formality. The documented cases of serious harm in infants have almost always involved homemade or unfortified plant milks combined with absent supplementation, rather than a well-constructed diet. Some specific points: rice milk should not be the main milk substitute for young children because of its inorganic arsenic content; energy density matters in small children, for whom high-fibre bulky diets can limit intake; and iodine, B12, iron, zinc, calcium, vitamin D and omega-3 all need explicit attention in pregnancy and lactation rather than assumption.

Is the environmental argument the same as the health argument?

No, and keeping them separate makes both stronger. The environmental evidence is considerably more robust: shifting diets away from ruminant meat substantially reduces greenhouse gas emissions, land use, freshwater use and pressure on biodiversity, and the magnitude of the difference between beef and pulses is large enough that the conclusion does not depend on methodological choices. The individual health argument is real but more qualified, depending heavily on what the plant-based diet actually contains. When the two are merged, readers reasonably suspect that a weaker argument is being propped up by a stronger unrelated one. The EAT-Lancet Commission attempted to combine them and attracted substantive criticism on affordability, micronutrient adequacy in low-income settings and cultural appropriateness — criticism that is better acknowledged than ignored.

How does GMJ News cover plant-based diets?

GMJ News covers the cohort evidence from EPIC-Oxford and Adventist Health Study-2, healthful versus unhealthful plant-based diet indices, mandatory B12 supplementation and the folate masking hazard, iron and zinc bioavailability with practical enhancement strategies, iodine as the most neglected deficiency risk, omega-3 conversion efficiency and algal oil, life stage considerations in pregnancy, infancy and childhood including the rice milk caution, ultra-processed vegan products, and the separate and stronger environmental argument including EAT-Lancet and its critics. Part of PHIG's contested science, nutrition and sustainability programmes.

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Plant-Based Diets

GMJ News knowledge hub · last reviewed September 2026 · Georgian Medical Journal

Summary Statistics Glossary GMJ news FAQ Documents Organizations Research

Well-constructed plant-based eating patterns have consistent cardiometabolic evidence behind them — lower LDL cholesterol, blood pressure, type 2 diabetes incidence and ischaemic heart disease across large cohorts including EPIC-Oxford and Adventist Health Study-2, with mechanisms that are well understood through fibre, unsaturated fat, potassium and lower saturated fat intake (WHO). Two qualifications are routinely omitted and both matter. First, “plant-based” and “healthy” are not synonyms: plant-based diet indices that separate healthful from unhealthful plant foods find that refined grains, sugar-sweetened beverages and ultra-processed vegan products carry the same adverse associations as any other ultra-processed diet, and the industry has enthusiastically adopted the label for products that qualify. Second, vitamin B12 supplementation is non-negotiable in vegan diets and its neurological consequences are irreversible if deficiency is prolonged — while iron, zinc, iodine, omega-3 and, in some settings, vitamin D and calcium require deliberate planning rather than assumption.

Key messages

SETTLED: well-constructed plant-based patterns have consistent cardiometabolic benefit

Large cohorts including EPIC-Oxford and Adventist Health Study-2, supported by mechanistic and trial evidence for intermediate outcomes, show lower LDL cholesterol, blood pressure, body mass index, type 2 diabetes incidence and ischaemic heart disease in vegetarian and vegan populations. The mechanisms are well understood — higher fibre, higher potassium, lower saturated fat, lower energy density, more unsaturated fat — rather than mysterious. This is among the better-supported dietary pattern findings available.

THE CRITICAL QUALIFIER: plant-based and healthy are not synonyms

Plant-based diet indices that separate healthful plant foods — whole grains, fruit, vegetables, nuts, legumes, oils, tea and coffee — from unhealthful ones — refined grains, potatoes, sugar-sweetened beverages, sweets and desserts — find that only the healthful index associates with reduced coronary heart disease and diabetes risk. The unhealthful plant-based index associates with increased risk. Ultra-processed vegan products carry the ultra-processed food risk profile regardless of their plant origin, and the food industry has adopted the label enthusiastically for products that qualify technically and benefit nobody.

NON-NEGOTIABLE: vitamin B12 supplementation in vegan diets

B12 is not reliably present in any unfortified plant food. Claims for spirulina, nori, tempeh and unwashed organic produce do not withstand scrutiny — spirulina contains pseudo-B12 analogues that are biologically inactive and may interfere with true B12 assays. Deficiency causes megaloblastic anaemia and, critically, subacute combined degeneration of the spinal cord, which is irreversible if prolonged. Folate supplementation can mask the haematological picture while neurological damage progresses. Every vegan requires either supplementation or reliably fortified foods, and this is not a matter of preference or careful planning.

REQUIRING DELIBERATE PLANNING: iron, zinc, iodine, omega-3, calcium, vitamin D

Non-haem iron is less bioavailable and is inhibited by phytate, polyphenols, tea and coffee; absorption is enhanced substantially by vitamin C consumed with the meal. Zinc absorption is similarly phytate-limited. Iodine intake can be very low where iodised salt is not used and dairy is excluded, with real thyroid consequences, and seaweed is an unreliable source with wide variability and excess risk. Conversion of ALA to EPA and DHA is inefficient, making algal oil the appropriate source. Calcium and vitamin D require attention where fortified alternatives are not used consistently.

LIFE STAGES REQUIRING SPECIALIST INPUT

Well-planned vegetarian and vegan diets are considered appropriate for all life stages by major dietetic bodies, with the emphasis on well-planned. Pregnancy, lactation, infancy, childhood and adolescence carry the least margin for error, and documented cases of severe harm in infants have almost always involved unfortified plant milks and absent supplementation rather than the dietary pattern per se. Rice milk should not be used as a primary milk substitute in young children because of inorganic arsenic content. These are strong arguments for dietetic support, not for discouraging the diet.

THE ENVIRONMENTAL ARGUMENT IS SEPARATE AND STRONGER

The evidence that shifting towards plant-based diets reduces greenhouse gas emissions, land use, freshwater withdrawal and biodiversity loss is considerably more robust than the individual health argument, and the two should be presented separately rather than merged. Conflating them weakens both: readers detect when a stronger unrelated argument is being used to reinforce a weaker one. The EAT-Lancet Commission proposed a planetary health diet and drew substantive criticism concerning affordability, micronutrient adequacy in low-income settings and cultural appropriateness, all of which deserve acknowledgement.

Key statistics

Lower risk

ischaemic heart disease, T2DM, hypertension and BMI in large vegetarian cohorts

EPIC-Oxford/AHS-2

Index matters

healthful plant-based index lowers risk; unhealthful plant-based index raises it

JACC/PLoS Med

B12 mandatory

no reliable unfortified plant source; spirulina contains inactive pseudo-B12 analogues

BDA/AND

Irreversible

subacute combined degeneration from prolonged B12 deficiency; folate can mask the anaemia

Neurology/Haematology

Vitamin C

consumed with meals substantially increases non-haem iron absorption

AJCN

Not rice milk

unsuitable as a primary milk substitute in young children due to inorganic arsenic

FSA/EFSA

Plant-based diets — where the disagreement actually lies

Source: Bars show strength of supporting evidence. The quality of the plant foods, not the absence of animal foods, drives most of the benefit.

Glossary of key terms

Plant-based diet indices
Nutritional epidemiologyDeveloped to address the observation that not all plant foods behave alike, these indices score dietary patterns in three ways. The overall plant-based diet index rewards all plant foods and penalises animal foods. The healthful plant-based index rewards whole grains, fruit, vegetables, nuts, legumes, vegetable oils, tea and coffee while penalising both animal foods and less healthful plant foods. The unhealthful plant-based index reverses this, rewarding refined grains, fruit juices, potatoes, sugar-sweetened beverages and sweets. Cohort analyses using these indices consistently show that the healthful index associates with reduced coronary heart disease and diabetes, while the unhealthful index associates with increased risk despite being entirely plant-based. This is the single most useful analytical development in the field.

Vitamin B12 — sources, testing and pitfalls
Clinical nutritionB12 is synthesised only by bacteria and archaea, reaching humans through animal foods or fortification. Reliable vegan sources are fortified foods — plant milks, nutritional yeast, some cereals and meat analogues — or supplements, typically cyanocobalamin 50-100 micrograms daily or 2000 micrograms weekly, doses set high because passive absorption is inefficient once intrinsic factor-mediated uptake is saturated. Serum B12 is an imperfect test with a wide indeterminate zone; methylmalonic acid and homocysteine are more sensitive functional markers. The critical clinical hazard is that high folate intake, common on plant-based diets, corrects the megaloblastic anaemia while neurological degeneration continues silently — which is why absence of anaemia does not exclude deficiency and why haematological screening alone is inadequate.

Iron and zinc bioavailability
Nutrition sciencePlant foods contain non-haem iron, absorbed at roughly 2-20% depending on the meal context, compared with 15-35% for haem iron. Absorption is inhibited by phytate, calcium, polyphenols in tea and coffee, and some fibres, and enhanced markedly by ascorbic acid and other organic acids consumed in the same meal. Practical implications: take tea and coffee between rather than with meals, include a vitamin C source with iron-containing meals, and use soaking, sprouting and fermentation to degrade phytate. Zinc absorption follows similar principles. Adaptation occurs over months, with upregulated absorption in habitual plant-based eaters, so short-term balance studies overstate the problem. Ferritin should be interpreted alongside CRP, since inflammation raises it independently.

Omega-3 fatty acids and conversion efficiency
BiochemistryAlpha-linolenic acid from flaxseed, chia, walnuts and rapeseed oil must be converted to eicosapentaenoic and then docosahexaenoic acid, and the conversion is inefficient — commonly cited as under 10% to EPA and considerably lower to DHA, with the efficiency reduced further by high linoleic acid intake competing for the same desaturase enzymes, and modestly higher in women. Vegetarians and vegans consequently have lower circulating EPA and DHA. Whether this translates into worse outcomes is not established, and vegetarian cohorts do not show excess cardiovascular disease. Algal oil supplements provide preformed DHA and EPA directly and are the sensible option where supplementation is desired, particularly in pregnancy and lactation where DHA supports fetal neurodevelopment.

Iodine — the most neglected deficiency risk
EndocrinologyDairy is a major iodine source in several countries because of its use in udder disinfection and cattle feed supplementation, so its exclusion removes a substantial contribution that few people are aware of. Plant milks are frequently not fortified with iodine even where they are fortified with calcium and B12. Iodine deficiency in pregnancy impairs fetal neurodevelopment irreversibly and is the leading preventable cause of intellectual disability worldwide. Seaweed is an unreliable substitute: content varies by orders of magnitude between species and batches, and kelp in particular can deliver excessive iodine causing thyroid dysfunction. Iodised salt or a supplement providing around 150 micrograms daily is the appropriate approach, with 250 micrograms in pregnancy and lactation.

EAT-Lancet and the planetary health diet
PolicyThe 2019 EAT-Lancet Commission proposed a reference diet intended to be both healthy and environmentally sustainable, involving substantially reduced red meat and increased legumes, nuts, whole grains, fruit and vegetables, framed within planetary boundaries for greenhouse gases, land, water, nitrogen and phosphorus. It attracted serious criticism on several grounds that deserve acknowledgement rather than dismissal: affordability analyses suggested the diet was unaffordable for a substantial proportion of the global population; micronutrient modelling raised concerns about iron, zinc, calcium and B12 adequacy, particularly for women of reproductive age in low-income settings; and cultural appropriateness varies enormously. The environmental analysis is more robust than the dietary prescription, and separating the two strengthens the argument.