This article was first published in the October 2018 edition of NHD Magazine. I enjoyed writing this article, as this hot topic is close to my heart.

Plant-based diets are becoming increasingly popular. This article will examine the nutrition considerations and health impact of plant-based diets.

Background:

A plant-based diet (PBD) involves consuming foods and drinks which mainly come from plant sources such as: fruit, vegetables, legumes, wholegrains, nuts and seeds. Most PBDs involve limiting or avoiding animal sources such as: meat, poultry, seafood, eggs and dairy.

There are different types of PBDs (as explained in table one) and different reasons for adopting these type of diets – ranging from health reasons and food preferences, to environmental protection and animal welfare.

Table One: Different Types of PBDs

Nutritional Considerations

Plant-based diets tend to be low in saturated fat and high in fruit, vegetables, wholegrains, beans, pulses, soy products, nuts and and seeds (i.e. high in fibre and antioxidants)¹.

Animal sources of food tend to be high in protein, but when calorie needs are met on a PBD protein requirements are usually met or exceeded¹.

Those on a PBD can get a good range of essential amino acids in their diet by including a variety of protein sources every day (as listed in table 2 below). PBDs can also be low in calcium, iron, vitamin B12, iodine, omega 3 and selenium^1-2. This is especially true with more restrictive diets such as veganism; for example a recent European study found that vegans were at a high risk of inadequate iodine and vitamin B12 intakes³. Furthermore, a limited amount of studies have found that vegetarian children may have low levels of vitamin D and vitamin B12⁴.

It is also important to remember that the recommended daily amount of iron for vegetarians is 1.8 times higher that for non-vegetarians, as iron which comes from plant sources (non-haem iron) acts less efficiently in our body than iron which comes from animal sources (haem iron)⁵. Although, the body may begin to use non-haem iron more efficiently in the absence of haem-iron. 

Overall, PBDs can be balanced and healthy as long as they include all important nutrients.

As PBDs are not automatically healthy, it is still important to include plenty of fruit, vegetables and fibre; while limiting foods which are high in saturated fat, salt and sugar.

Extra dietary planning, which may include support from a registered dietitian, can be needed for groups which are more nutritionally vulnerable such as: pregnant and breastfeeding women, babies and young children. Supplements may also be indicated, depending on the level of dietary restriction. For example supplements which include vitamin B12 and iodine are often needed by those following a vegan diet^2,6.

For details about important nutrients and how to achieve a nutritionally balanced PBD check out this blog post: Nutritional Advice for Vegetarians & Vegans

Health Outcomes

Studies have found that PBDs lead to lower levels of total and low-density lipoprotein (LDL) cholesterol levels and improvements in serum glucose levels and inflammation^1,8.

These factors are thought to contribute to a reduced risk of chronic disease overall. For example, a recent meta-analysis of observational studies by Dinu et al. found that a vegetarian diet was associated with healthier ranges for BMI, lipid variables and fasting glucose as well as being modestly associated with reduced rates of ischemic heart disease and cancer⁹. However there was no significant association found for: all-cause mortality, other types of cardiovascular disease and stroke, cancer mortality or breast cancer incidence. There is less available evidence in terms of vegan diets. However, Dinu et al. found no association between a vegan diet and improved all-cause mortality, and a possible association was found between a vegan diet and a reduced incidence of cancer⁹.

A limited amount of conflicting evidence has found that there may be a lower risk of dementia among those who follow a PBD, but more evidence is needed to investigate this¹⁰.

For those with type 2 diabetes, PBDs have been associated with improved glycemic control¹¹. PBDs have also been linked with a lower risk developing type 2 diabetes in observational studies based in Adventist populations^12-13.

It is important to be aware of the numerous confounding factors which effect studies of PBDs which aren’t always fully corrected for. For example, those who follow PBDs are more likely to be: female young adults, educated, non-smokers and physically active¹⁴.

Furthermore, a high intake of fruit and vegetables (regardless of whether meat and dairy is included) is associated with a lower risk of heart disease, cancer and early death^15-16. A large systematic review from 2017 found that 5.6 million early deaths worldwide in 2013 may have been related to having a low intake of fruit and vegetables¹⁶.

Benefits of animal-based foods should also be highlighted. A moderate intake of lean red meat as part of an overall balanced diet is associated with a low risk of chronic disease and improvements in overall nutrient profile¹⁷. Similarly, some studies have found that including dairy as part of a vegetarian diet carries more health benefits than avoiding dairy; in terms of bone, heart and metabolic health¹⁸. Meat and dairy can also provide energy and important nutrients in lower volumes than plant-based foods, which can be especially important for those who are unwell or those with a poor appetite.

There are some negative health outcomes associated with PBDs. A study by Appleby et al. (2007)¹⁹ found that although vegetarians and pescetarians had a similar fracture risk to meat eaters, vegans had a higher fracture risk which correlated with a lower average intake of calcium. Some studies have also found a higher risk of anaemia in those following PBDs^20-21.

PBDs can feel overly restrictive for some people, which may lead to a disordered relationship with food. For example, studies have found that vegetarians may have a higher risk of: disordered eating, binge eating and extreme behaviour related to controlling weight^22-23. But there is not enough evidence as to whether vegetarianism has a causal role in the development of an eating disorder, or whether this emerges in order to mask symptoms of an existing eating disorder²³.

Well planned plant-based diets can be used at all stages of life.

Normal growth and development has been observed in infants, children and adolescents who follow a PDB^24-26. However, raw, macrobiotic, and fruitarian diets have been associated with malnutrition and impaired growth in infants²⁷.

Conclusion

Well planned PBDs are associated with a healthy nutritional profile and a reduced risk of chronic diseases. However some of the supporting evidence for this can be confounded by the fact that vegetarians and vegans tend to make other healthy lifestyle choices beyond diet.

Animal-based foods are also nutritious, and cutting out food groups runs the risk of nutritional deficiency and related health problems.

Although most people would benefit from eating a more PBD, many of the benefits can be achieved by eating more plant-based products and less animal-based products; without avoiding animal-based products all together.

Therefore a ‘flexitarian’ approach may be a more realistic and balanced way for many people to adopt a PBD.

References:

1. Melina et al. (2016) “Position of the Academy of Nutrition and Dietetics: Vegetarian Diets” [available via: https://jandonline.org/article/S2212-2672(16)31192-3/abstract]
2. BDA Food Fact Sheet ‘Vegetarian Diets’ [accessed June 2018 via: https://www.bda.uk.com/foodfacts/vegetarianfoodfacts.pdf]
3. Sobeicki et al. (2015) “High compliance with dietary recommendations in a cohort of meat eaters, fish eaters, vegetarians, and vegans: results from the EPIC-Oxford study” [available via: https://www.sciencedirect.com/science/article/pii/S0271531716000026]
4. Schurmann et al. (2017) “Vegetarian diets in children: a systematic review” [available via: https://link.springer.com/article/10.1007/s00394-017-1416-0]
5. Food and Nutrition Board, Institute of Medicine (2000) “Dietary Reference Intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc” [Available via: http://www.nap.edu/books/0309072794/html/]
6. First Steps Nutrition “Eating well: vegan infants and under-5s” [accessed  June 2018 via: http://www.firststepsnutrition.org/pdfs/Eating_well_for_veg_infants_for_web.pdf]
7. The Manual of Dietetic Practice – 5th Edition (2014): Table A2.1 p. 923
8. Eichelmann  et al. (2016) ‘Effect of plant‐based diets on obesity‐related inflammatory profiles: a systematic review and meta‐analysis of intervention trials” [accessed via: https://onlinelibrary.wiley.com/doi/full/10.1111/obr.12439]
9. Dinu et al. (2017) “Vegetarian, vegan diets and multiple health outcomes: a systematic review with meta-analysis of observational studies” [Available via: https://www.researchgate.net/publication/293329136]
10. Giemet al. (1993) “The incidence of dementia and intake of animal products: preliminary findings from the Adventist Health Study” [available via: https://www.ncbi.nlm.nih.gov/pubmed/8327020]
11. Yokoyama (2014) “Vegetarian diets and glycemic control in diabetes: a systematic review and meta-analysis” [available via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4221319/]
12. Tonstad et al. (2013) “Vegetarian diets and incidence of diabetes in the Adventist Health Study-2”
13. Orlich et al. (2014) “Vegetarian diets in the Adventist Health Study 2: a review of initial published findings”
14. Cramer et al. (2017) “Characteristics of Americans choosing vegetarian and vegan diets for health reasons” [available via: https://www.ncbi.nlm.nih.gov/pubmed/28689610]
15. Wang et al. (2014) “Fruit and vegetable consumption and mortality from all causes, cardiovascular disease, and cancer: systematic review and dose-response meta-analysis of prospective cohort studies” [available via: https://www.bmj.com/content/349/bmj.g4490.short]
16. Aune et al. (2017) :Fruit and vegetable intake and the risk of cardiovascular disease, total cancer and all-cause mortality—a systematic review and dose-response meta-analysis of prospective studies” [available via: https://academic.oup.com/ije/article/46/3/1029/3039477#.WK8GCT_AOQE] 
17. McAfee et al. (2009) “Red meat consumption: An overview of the risks and benefits” [available via: https://www.sciencedirect.com/science/article/abs/pii/S0309174009002514]
18. Weaver (2009) “Should dairy be recommended as part of a healthy vegetarian diet?” [available via: http://ajcn.nutrition.org/content/89/5/1634S.short]
19. Appleby et al. (2007) “Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford” [available via: https://www.ncbi.nlm.nih.gov/pubmed/17299475]
20. Ball & Bartlett (1999) “Dietary intake and iron status of Australian vegetarian women” [available via: https://www.ncbi.nlm.nih.gov/pubmed/10479197]
21. Wilson & Ball (1999) “Nutrient intake and iron status of Australian male vegetarians” [available via: https://www.ncbi.nlm.nih.gov/pubmed/10201799]
22. Robinson-O’Brien (2009) “Adolescent and Young Adult Vegetarianism: Better Dietary Intake and Weight Outcomes but Increased Risk of Disordered Eating Behaviors” [available via: https://jandonline.org/article/S0002-8223(08)02327-4/abstract]
23. Heiss et al. (2017) “Vegetarianism and Eating Disorders” [available via: https://www.researchgate.net/publication/317336503_Vegetarianism_and_Eating_Disorders]
24. Badger et al. (2009) “The health implications of soy infant formula” [available via: https://www.ncbi.nlm.nih.gov/pubmed/19357221]
25. O’Connell et al. (1989) “Growth of vegetarian children: the Farm Study. Pediatrics” [available via: https://www.ncbi.nlm.nih.gov/pubmed/2771551]
26. Rosell et al. (2005) “Height, age at menarche, body weight and body mass index in lifelong vegetarians” [available via: https://www.ncbi.nlm.nih.gov/pubmed/16277803]
27. Dagnelie & van Staveren (1994) “Macrobiotic nutrition and child health: results of a population-based, mixed-longitudinal cohort study in The Netherlands” [available via: https://www.ncbi.nlm.nih.gov/pubmed/8172122]