Vegetarian and Vegan Diets: Nutrients to Monitor

Hundreds of millions of people follow vegetarian diets for religious, cultural, ethical, environmental or health reasons, and the number following vegan diets has grown rapidly in many countries. For practitioners, plant based diets are neither a problem to be corrected nor a cure to be prescribed. They are dietary patterns with distinctive strengths and specific nutritional vulnerabilities, and good care means knowing both.

Definitions

Terminology matters because nutritional risks differ considerably between patterns.

• Lacto ovo vegetarian: no meat or fish, but includes dairy and eggs.
• Lacto vegetarian: includes dairy but not eggs, common in parts of South Asia.
• Pescatarian: excludes meat but includes fish.
• Vegan: excludes all animal products, including dairy, eggs and often honey.
• Flexitarian or plant forward: mainly plant based with occasional animal foods.

A lacto ovo vegetarian who eats dairy and eggs daily has very different needs from a vegan, and a vegan eating a varied whole food diet has different needs from one relying on refined and processed plant foods.

The health picture

Major dietetic organisations have concluded that appropriately planned vegetarian and vegan diets are healthful, nutritionally adequate and may provide health benefits in the prevention and treatment of some diseases, and are appropriate for all stages of life.

Observational studies support benefits: vegetarians generally have lower body mass index, LDL cholesterol and blood pressure, and lower rates of ischaemic heart disease and type 2 diabetes. The picture is not entirely one sided, however. In the EPIC Oxford cohort, vegetarians had lower rates of ischaemic heart disease but somewhat higher rates of haemorrhagic stroke than meat eaters, and vegans had a higher risk of fractures, particularly hip fractures, possibly related to lower calcium and protein intakes and lower body weight. These findings reinforce the importance of planning rather than undermining plant based diets.

The quality of the plant based diet matters as much as its label. Diets built on whole grains, legumes, vegetables, fruit, nuts and seeds are associated with benefits; plant based diets high in refined grains, sugary drinks and processed foods are not.

Nutrients to monitor

Vitamin B12

Vitamin B12 is found naturally almost exclusively in animal foods. Vegans cannot obtain adequate B12 from unfortified plant foods, and claims that fermented foods, seaweed or unwashed vegetables provide meaningful amounts are not supported; some contain inactive analogues. Vegans need a reliable source: a supplement or regular fortified foods. Vegetarians who eat dairy and eggs may meet needs but are still at higher risk than omnivores, particularly if intake of these foods is low. Deficiency can cause anaemia and neurological damage, and in infants of vegan mothers who are not supplemented, it can cause serious developmental harm.

Iron

Plant foods contain non haem iron, which is less efficiently absorbed than the haem iron in meat. Absorption is inhibited by phytates, polyphenols in tea and coffee, and calcium, and enhanced by vitamin C. Vegetarians often have iron intakes similar to omnivores but lower iron stores. Practical measures include legumes, whole grains, dark leafy greens and seeds, combined with vitamin C rich foods; avoiding tea and coffee with meals; and soaking, sprouting or fermenting legumes and grains to reduce phytates. Women of reproductive age need particular attention.

Zinc

Zinc absorption is also reduced by phytates. Legumes, whole grains, nuts, seeds and fermented soy foods are useful sources, and the same preparation techniques that improve iron availability help.

Iodine

Iodine intake depends heavily on dairy, fish, eggs and iodised salt, so vegans who do not use iodised salt are at risk of deficiency. Seaweed is an unreliable source because iodine content varies enormously, and some types contain very high levels that can cause thyroid dysfunction. Iodised salt or a supplement providing a standard dose is more dependable.

Long chain omega 3 fatty acids

EPA and DHA are found mainly in fish and seafood. Plant foods such as flaxseed, chia, walnuts and hemp provide alpha linolenic acid, which the body converts to EPA and DHA only inefficiently. Vegetarians and vegans have lower blood levels of EPA and DHA. Algal oil supplements provide a plant based source of DHA and EPA and may be considered, particularly in pregnancy and breastfeeding.

Calcium

Lacto vegetarians usually meet calcium needs through dairy. Vegans need calcium fortified plant milks and yoghurts, calcium set tofu, low oxalate green vegetables such as kale and bok choy, and other sources, or a supplement if intake is low.

Vitamin D

Vitamin D status depends mainly on sunlight and is a concern for many people regardless of diet. Vegans have fewer dietary sources, so fortified foods or supplements may be needed, particularly at higher latitudes.

Protein

Most vegetarians and vegans meet protein needs when they eat enough food and include legumes, soy foods, whole grains, nuts and seeds. Protein needs deserve more attention in older adults, athletes, people with small appetites and those losing weight, and slightly higher intakes may be appropriate on vegan diets to account for digestibility.

A monitoring summary

Life stages that need extra care

Pregnancy and breastfeeding: B12, iron, iodine, DHA, choline, calcium and vitamin D all need attention; vitamin B12 supplementation is essential for vegan mothers.

Infants and children: energy density, protein, B12, iron, zinc, iodine, calcium and vitamin D. Vegan diets for young children require particularly careful planning, ideally with a dietitian.

Older adults: protein to protect muscle, B12 given reduced absorption with age, calcium and vitamin D for bone health.

Athletes: total energy, protein and iron.

Respecting the reasons

For many patients, vegetarianism is not a dietary preference but a religious or ethical commitment. Practitioners should never suggest abandoning it for nutritional reasons without exploring alternatives; in almost every case, needs can be met within the pattern. Understanding the patient’s reasons also clarifies what is acceptable. A patient who is vegetarian for religious reasons may accept dairy but not eggs; a vegan for ethical reasons may accept algal oil and B12 supplements readily once their origin is explained.

An illustrative case

A 29 year old woman, vegan for 5 years, presents with fatigue, pins and needles in her feet and low mood. She does not take supplements, believing a whole food diet provides everything. Her diet is varied and rich in vegetables, but she uses uniodised sea salt and drinks unfortified plant milk. Her doctor finds a low B12 with raised methylmalonic acid and a low ferritin, and treats both. Her plan adds a regular B12 supplement, iodised salt, fortified plant milk, vitamin C rich foods with iron sources and tea between rather than with meals. She plans pregnancy in the next few years, so algal DHA is discussed. Her symptoms improve over several months, and her diet remains fully vegan.

Planning, not permission

The question for practitioners is not whether vegetarian and vegan diets are healthy but whether a particular person’s version of them is well planned. With attention to a short list of nutrients, a small number of supplements and regular review at life stages of higher need, plant based diets can provide everything a person needs, alongside substantial health benefits.