Nutrition

Topics

• Algal omega-3 EPA and DHA

  Microalgae are a non-fish source of the long-chain omega-3 fats DHA and EPA. Adults following vegetarian and vegan diets take in less EPA and DHA and have lower blood levels than meat-eaters, and randomised trials show that algal-derived DHA supplements raise blood DHA and the omega-3 index in vegan, vegetarian and omnivorous adults, with algal-oil capsules delivering DHA as well as cooked salmon. Algal DHA lowered blood triglycerides in a meta-analysis of small trials, but no trials have tested algal omega-3 against hard health outcomes in vegans, and large trials of mostly fish-oil omega-3 found little or no effect on mortality or cardiovascular events.

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• Calcium

  Adults following a vegan diet eat substantially less calcium than other diet groups and, in large observational studies, have lower bone mineral density and higher fracture rates, especially hip fractures. In adults over 50, raising calcium intake from food or supplements produces small, non-progressive gains in bone mineral density; dietary calcium intake is not associated with fracture risk, and trial evidence on fractures is mixed, with combined calcium and vitamin D looking more promising than vitamin D alone. Large trials and meta-analyses link calcium supplements with more kidney stones and possibly more heart attacks.

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• Choline

  Choline is an essential nutrient: in controlled feeding studies most adults deprived of dietary choline developed fatty liver or muscle damage that reversed when choline was restored. Surveys suggest most adults and most pregnant women eat less than the adequate intake, and vegetarian and vegan diets tend to supply less because choline is concentrated in animal foods. Evidence that extra choline in pregnancy improves child development is insufficient, cohort links between higher intake and better cognition are observational, and very high intakes have known side effects.

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• Daily food targets

  Daily food-group targets in dietary guidance rest mainly on dose-response meta-analyses of large prospective cohorts. In adults, eating more fruit and vegetables, whole grains, dietary fibre and nuts each day is associated with lower all-cause mortality and a lower risk of cardiovascular disease, with the lowest mortality seen at about five servings of fruit and vegetables and about 25 to 29 g of fibre a day, while more red and processed meat is associated with higher risk. The WHO sets population targets of at least 400 g of fruit and vegetables and at least 25 g of fibre a day for everyone older than 10. Because the evidence is mostly observational, the strongest grade here is moderate.

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• Fermented foods and polyphenols

  Randomised trials in healthy adults link eating fermented foods with modest improvements in bowel habits and gut comfort, and one small trial found a fermented-food diet raised gut microbiota diversity and lowered inflammatory markers; the certainty of this evidence is mostly low. Cohort studies associate fermented milks, cheese and chocolate with lower mortality. Among polyphenols, cocoa flavanols have moderate-certainty trial evidence for a small short-term fall in blood pressure, and cohort studies associate flavan-3-ol intake with better cardiometabolic outcomes. Concentrated green tea extract supplements are the main safety exception, with case reports of liver injury.

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• Iodine

  Iodine is needed to make thyroid hormones, which regulate growth, development and metabolism, and low intake early in life impairs cognition and growth. Adults following vegan diets have the lowest iodine intake and status of any dietary group studied, especially where salt is not routinely iodised. Population salt iodisation programmes are linked with adequate iodine status, while trials of iodine supplements in pregnancy in mildly to moderately deficient settings show better maternal iodine status but no clear infant benefit. Too much iodine, including from some seaweeds such as kelp, is also linked with thyroid dysfunction.

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• Iron

  Adults following vegetarian or vegan diets have lower iron stores (serum ferritin) than meat-eaters, because plant foods supply only non-haem iron, which is less well absorbed; mean haemoglobin is similar across diet patterns, while the evidence on anaemia prevalence is mixed. Eating ascorbate-rich fruit with meals probably raises ferritin and haemoglobin modestly. Adding vitamin C to oral iron supplements adds little, and iron supplements raise iron status in menstruating women at the cost of more gastrointestinal side effects.

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• Legumes, whole grains, nuts

  Randomised trials show that eating tree nuts or dietary pulses (beans, chickpeas, lentils, peas) lowers LDL cholesterol in adults, and large meta-analyses of cohort studies link higher whole grain and nut intake with lower cardiovascular disease and all-cause mortality. Cohort evidence for legumes and cardiovascular outcomes is weaker and graded low to very low by its authors. A modelling study that combines these meta-analyses estimates that eating more legumes, whole grains and nuts accounts for much of the predicted gain in life expectancy from a shift away from a typical Western diet, but its figures are population estimates under stated assumptions.

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• Protein and leucine

  Expert groups conclude that older adults need more dietary protein than younger adults, and many older adults eat less than that. In randomised trials, eating more protein gave small extra gains in lean mass and leg strength in healthy adults doing resistance exercise, with little further gain above about 1.6 g per kilogram of body weight a day. Leucine supplements raised muscle protein synthesis in older adults without a measurable gain in lean mass. Plant and animal protein sources produced similar changes in absolute lean mass and strength, although many plant proteins carry less leucine, lysine or methionine. In healthy adults, higher-protein diets did not change kidney function in trials.

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• Selenium

  Selenium is an essential trace element found mostly in animal foods and in Brazil nuts, and a small 2025 trial found lower selenium intake in adults following a vegan diet than in omnivores, with Brazil nut butter raising selenium status as well as a supplement did. Large, well-conducted randomised trials found that selenium supplements did not lower cancer or cardiovascular risk in adults, and pooled trials suggest a small increase in type 2 diabetes risk. In people with Hashimoto thyroiditis, trials found lower thyroid antibody and TSH levels with selenium. Intakes above the EFSA upper level are possible with high-dose supplements or regular Brazil nut eating.

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• Time-restricted eating

  Time-restricted eating limits daily food intake to a set window, typically 4 to 10 hours in trials. In adults, mostly with overweight or obesity, it reduces body weight compared with an unrestricted usual diet, but randomised trials and meta-analyses mostly find no clear extra benefit over ordinary daily calorie restriction of the same intensity. In adults with prediabetes or type 2 diabetes it modestly lowered fasting blood glucose but not HbA1c. Trials report no overall excess of adverse events, though one meta-analysis found more hunger than with calorie-matched diets, and most trials are short.

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• Vitamin B12

  Plant foods are not a reliable source of vitamin B12, so adults on an unsupplemented vegan diet have lower B12 status and more functional deficiency than omnivores, while supplement users show better biomarker levels. Long-term deficiency affects red blood cell production and the nervous system and is most serious in infants. In adults who are not deficient, randomised trials found no benefit of extra B12 for cognition or mood.

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• Vitamin D

  In Australia and New Zealand most vitamin D comes from sunlight rather than food, so low status is most common in people who get little sun, such as housebound or institutionalised older adults and people with dark skin. In randomised trials, vitamin D on its own did not reduce fractures or falls or meaningfully change bone density in adults not selected for deficiency, while vitamin D combined with calcium was linked to a small reduction in fractures in older adults. Trials also found a small overall reduction in acute respiratory infections. Vitamin D3 raised blood levels more than D2 in trials, mainly at large infrequent doses, and people on plant-based diets tend to have lower vitamin D intake and status.

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• Vitamin K2

  Vitamin K2 (menaquinones, including MK-7 from the fermented soybean food natto) supports the carboxylation of vitamin K-dependent proteins such as osteocalcin, and supplementation trials consistently shift these markers. Effects on outcomes that matter are less certain: pooled trials in postmenopausal women show small lumbar spine bone density gains that shrink when higher-risk-of-bias trials are removed, fracture results are inconsistent, and effects on artery calcification and stiffness are mixed. MK-7 supplements can weaken the effect of vitamin K antagonist anticoagulants even at low intakes.

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• Whole-food plant pattern

  Eating patterns built mostly on whole plant foods (vegetables, fruits, whole grains, legumes, nuts) are linked in large cohort studies with lower cardiovascular, type 2 diabetes and all-cause mortality risk, and randomised trials show vegetarian and vegan diets lower LDL cholesterol. The quality of the plant foods matters: plant patterns heavy in refined and ultra-processed plant foods are linked with higher, not lower, risk.

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• Zinc

  Zinc is an essential trace mineral. Populations following vegetarian and vegan diets tend to have lower zinc intakes, and pooled studies also show lower serum zinc, largely because phytate in whole grains, legumes and seeds reduces zinc absorption; food preparation such as soaking, sprouting, fermenting and leavening reduces phytate. Trials of zinc taken during a common cold suggest shorter colds with more minor side effects, at low certainty. Excessive zinc intake over time can disrupt copper metabolism.

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