Vegan Diets

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This article was first published in the Irish Nutrition and Dietetic Institute Spring 2019 Professional Nutrition & Dietetic Review (Volume 4 Issue 1).

A vegan diet involves avoiding all animal products – including meat, poultry, fish, dairy, eggs and honey. Animal-derived products used in cosmetics, clothing and furniture (such as leather) are also avoided. This is becoming an increasingly popular lifestyle choice.

In the UK veganism has increased by roughly 260% over the past 10 years.1

In Ireland it is estimated that: 2% of the population are vegan, although 41% of women and 30% of men are thought to avoid or limit their intake of dairy.2,3

Motivations for ‘going vegan’ can vary a lot – some are motivated by ethical, animal welfare and environmental reasons, whereas others are motivated by perceived health benefits.

This article will explore the impact of a vegan diet, as well as the practical dietary considerations.

Environmental Impact

Meat and dairy are the main contributors to diet-related carbon emissions world-wide.4

It is estimated that switching to a plant-based diet on a global scale would reduce:5

  • Land use by 76%
  • Greenhouse gas emissions by 49%
  • Acidification by 50% (i.e. when the pH of water or soil reduces as a result of pollution, which can harm biodiversity)
  • Eutrophication 49% (i.e. when water becomes overly enriched with nutrients which boosts the growth of plants and algae, hence oxygen supply depletes)

But sustainable eating is complex, and there are multiple factors to consider. For example,  meat and dairy can be produced in sustainable ways, and not all plant-based alternatives are environmentally-superior (although most are).

Furthermore, for a diet to be sustainable it also needs to be nutritionally adequate and culturally acceptable.6

So meat and dairy products can have a place in a sustainable diet, but it depends on the production methods used and the quantities consumed.

Health Impact

Most studies have evaluated the health impact of vegetarian diets, rather than vegan diets.

A recent systematic review found that compared to omnivores, vegan diets are associated with lower: BMI, total and LDL cholesterol, and blood glucose levels.7

This review also found that following a vegan diet was linked with a reduced risk of cancer.7  

But there are common characteristics linked with vegans which may impact the results of some of the studies in this review.

For example, most vegans in Western countries tend to be: young females, within the healthy BMI range, health conscious, physically active, educated and non-smokers.1,8

Furthermore, some of the health benefits of veganism may be mainly attributed to a high intake of plant-based foods, rather than the restriction of animal products.

Some studies have found a link between vegetarian diets and disordered eating; particularly among adolescents.9,10 However the direction of this relationship isn’t clear, and there appears to be limited research related specifically to veganism and disordered eating. But it is important to be aware that, anecdotally, vegan diets can be used to mask the symptoms of an eating disorder.

Animal-based products provide important nutrients such as: protein, omega-3 fat, B-vitamins (including B12), iodine, calcium, iron,  zinc and selenium. Therefore, unbalanced vegan diets can lead to nutrient deficiencies, and a higher risk of anaemia or osteoporosis.11,12

Well-planned vegan diets can be implemented at any age. However, the risk of nutritional inadequacy on this diet is higher for for vulnerable groups such as: those who are malnourished, older people, infants and young children.

How to Achieve a Balanced Vegan Diet

‘The Vegan Plate’ (which can be found via the Vegan Society website) is a great resource.

This shows the variety of food needed in order to achieve a balanced vegan diet. Importantly, The Vegan Plate also highlights that fortified food and supplements are often needed, in order to meet micronutrient requirements.

Image reference: The Vegan Plate by Brenda Davis (RD) and Vesanto Melina (RD) acccessed via:

Vegan sources of protein include: beans, lentils, chickpeas, tofu, tempeh, soya milk, mycoprotein (i.e. Quorn), seitan, nuts, seeds, bread, grains, and imitation meat made using soya, pea and wheat protein.

Most people already consume more than enough protein, but this can be more of a concern for vegans, especially those who have high protein requirements or a poor appetite.

It is also important that vegans consume a good variety of protein sources in order to obtain all nine essential amino acids. For example, grains tends to be low in lysine, whereas legumes tend to be low in methionine.

Vegan foods which contain all nine essential amino acids include: soya beans, quinoa, amaranth, hempseed and buckwheat.  

It can be difficult to consume enough omega-3 on a vegan diet, as fish is the best dietary source. Alpha-linolenic acid (ALA) is a form of omega-3 which can be found in a variety of vegan foods, such as: walnuts, walnut oil, chia seeds, linseeds, linseed oil, soybeans, soybean oil, hemp seeds, rapeseed oil, hazelnuts, pecans, and green leafy vegetables.

However, ALA isn’t converted very efficiently to the main forms of omega-3 which are used by our body – eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).13

Seaweed contains EPA and DHA, but the British Dietetic Association recommend consuming seaweed no more than once per week, especially if pregnant, as this can provide too much iodine.14 Some omega-3 fortified spreads and breads are available, although these aren’t always readily available in Ireland.

It can also be challenging to consume enough vitamin B12 on a vegan diet. Dietary sources include: marmite, nutritional yeast, fortified breakfast cereals and fortified plant-based milks.

Dairy is one of the main dietary sources of iodine in the UK and Ireland, but some companies are starting to add this to fortified plant based milks (always check the label).13 Iodised salt is another dietary source – however this can be difficult to source in Ireland. Seaweed also contains iodine, but as mentioned above, this may contain an excessive amount of iodine.13

Vegans can obtain iron from: iron fortified breakfast cereals, wholegrains, beans, nuts, sesame seeds, yeast extract, dried fruit and green leafy vegetables.

Vegans and vegetarians need to consume 1.8 times more iron than omnivores, as plant-based sources of iron are non-haem.15

n American company called Impossible Foods has invented a plant-based source of haem iron using genetically-modified soya roots, but unfortunately this isn’t available in Europe at present. Sources of vitamin C should be consumed alongside sources of iron in order to boost absorption.

Vegan sources of calcium include: fortified dairy alternatives (e.g. soya, oat or nut milks), tofu, calcium fortified orange juice, green leafy vegetables, beans, pulses, dried fruit, nuts, seed and bread. Dairy products contain more calcium than plant-based versions found in their natural state (such as green leafy vegetables).

However, there is some evidence that the calcium found in plant-based sources, like boiled kale and pak choi, may be more bioavailable than the calcium which is found in dairy.16  

Vitamin D is best obtained via sunlight or supplements.17 Vitamin D can also be found in small amounts in: mushrooms which have been exposed to UV light, fortified margarine, bread and fortified breakfast cereals.

Vegan sources of zinc include: fortified breakfast cereals, nuts, seeds, wholegrains, green leafy vegetables, root vegetables, beans and fermented soya products (e.g. miso and tempeh).

It is also thought that soaking and rinsing dried beans prior to cooking increases our absorption of zinc from these foods.18  

Brazil nuts are a great vegan source of selenium. In fact one Brazil nut contains the adult daily requirement of selenium.19   


Overall, a balanced vegan diet which includes some fortified foods can provide a range of vital nutrients.

However, most vegans living in Ireland should consider supplementing with vitamin B12, vitamin D and iodine (depending on the individual and their overall diet).20

Supplementing with other nutrients such as omega 3, iron and calcium may need needed on a case-by-case basis.20-21

Supplementation can be particularly important for nutritionally-vulnerable groups such as vegan: infants, pregnant or breastfeeding women, older people, those with a limited diet or those who are malnourished. But as with all supplements, it is important to stick to a safe dose and to avoid combining numerous supplements which contain the same nutrients.


  1. Ipsos Mori. Vegan Society Poll [Internet]. 2016. Available from:
  2. Bord Bia. Out with Veganuary, in with Februdairy. February 2018 [cited 14/11/2018]. Available from:,inwithfebrudairy.aspx
  3. National Dairy Council. The Dairy – NDC Seeks to Understand Attitudes Towards Dairy and to Understand How These are Changing. September 2017 [cited 14/11/2018]. Available from:
  4. Food and Agriculture Organization of the United Nations. Tackling Climate Change Through Livestock. 2013 [cited 13/11/2018]. Available from:
  5. Poore J, Nemecek T. Reducing food’s environmental impacts through producers and consumers. Science. 2018; 360(6392): 987-992. Available from:
  6. FAO (2010) “Final document: International Scientific Symposium Biodiversity and Sustainable Diets: United against Hunger. 3-5 November 2010” –
  7. Dinu M, Abbate R, Gensini GF, Casini A & Sofi F. Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies. Critical Reviews in Food Science and Nutrition. 2017; 57(17): 3640-3649. Available from:  
  8. Cramer H, Kessler CS, Sundberg T, Leach MJ, Schumann D, Adams J, Lauche R. Characteristics of Americans Choosing Vegetarian and Vegan Diets for Health Reasons. J Nutr Educ Behav. 2017; 49(7): 561-567. Available from:
  9. Robinson-O’Brien R, Perry CL, Wall MM, Story M, Neumark-Sztainer D. Adolescent and Young Adult Vegetarianism: Better Dietary Intake and Weight Outcomes but Increased Risk of Disordered Eating Behaviors. Journal of the Academy of Nutrition and Dietetics. 2009; 109(4): 648–655. Available from:  
  10. Heiss S, Hormes JM, Timko CA. Vegetarianism and Eating Disorders. Vegetarian and Plant-Based Diets in Health and Disease Prevention, 2017:51-69. Available from:
  11. Appleby P, Roddam A, Allen N, Key T. Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford. Eur J Clin Nutr. 2007; 61(12):1400-6. Available from:
  12. Waldmann A, Koschizke JW, Leitzmann C, Hahn A. Dietary iron intake and iron status of German female vegans: results of the German vegan study. Ann Nutr Metab. 2004; 48(2): 103-8. Available from:
  13. British Dietetic Association. Omega-3 Food Fact Sheet – British Dietetic Association [Internet]. 2017 [cited : 13/11/2018]. Available from:
  14. British Dietetic Association. Iodine Food Fact Sheet  [Internet]. 2016 [cited : 13/11/2018]. Available from:
  15. Institute of Medicine. Dietary Reference Intakes For: Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington: National Academy Press; 2001. Available from:
  16. Kamchan A, Puwastien P, Sirichakwal PP, Kongkachuichai R. In vitro calcium bioavailability of vegetables, legumes and seeds. Journal of Food Composition and Analysis. 2004; 17(3–4): 311-320. Available from:
  17. Scientific Advisory Committee on Nutrition. Vitamin D and Health. 2016. Available from:
  18. Gibson RS, Yeudall F, Drost N, Mtitimuni B, Cullinan T. Dietary interventions to prevent zinc deficiency. Am J Clin Nutr 1998;68:484S–7S   
  19. National Institute of Health. Selenium – Consumer [Internet]. 2016 [cited 13/11/2018]. Available from:
  20. Messina G. Recommended Supplements for Vegans. 2010 [cited 13/11/2018]. Available from:
  21. Lane K, Derbyshire E, Li W, Brennan C. Bioavailability and potential uses of vegetarian sources of omega-3 fatty acids: a review of the literature. Crit Rev Food Sci Nutr. 2014; 54(5): 572-9. Available from:


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