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Nutrition research review: The safe and effective use of plant-based diets with guidelines for health professionals

Plant-based diets have soared in popularity in recent years. It is important that health professionals have a good understanding of how we can support patients consuming a plant-based diet to achieve optimal nutrition.

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A plant-based diet is a broad label that captures the spectrum of diets comprised mainly of plant-based foods. In this paper, the definition used includes diets that range from including only plant-based foods (e.g., vegan) through to diets that are predominantly plant-based but may include animal products such as eggs and dairy (e.g., lacto-ovo vegetarian)[1].

Plant-based diets and chronic diseases

Plant based diets generally deliver more dietary fibre and are rich in polyphenols as they often contain proportionally more fruits, vegetables, wholegrains, legumes, and nuts/seeds than an omnivore dietary pattern. These dietary components deliver metabolic and anti-inflammatory benefits and are associated with reductions in chronic disease risk factors.

Cardiovascular disease (CVD): Evidence supports that a well-balanced plant-based diet that is rich in fruits, vegetables, wholegrains, legumes, nuts and seeds is associated with reductions in CVD risk factors including body mass index, waist circumference[2, 3], blood lipids[4], blood glucose[2], inflammation[5] and blood pressure[6].

Type 2 Diabetes Mellitus (T2DM): Observational research indicates that vegan and vegetarian populations are at lower risk of developing T2DM compared to non-vegetarians (e.g., [7]). Similarly, vegetarian diets, along with other plant-based diets such as the vegan, Mediterranean, and the Dietary Approaches to Stop Hypertension (DASH) diets have been associated with a reduction in HbA1c and other metabolic risk factors[8].

Cancer: Plant foods are a rich source of phytochemicals and plant food groups have chemo-protective properties. Nuts, fruits, legumes, and vegetables are all associated with reduced cancer risk[9]. Red meat intake at 100-120 g/day has been found to significantly increase the risk of a range of cancers when compared to not eating meat[10].

Bone health: There is some evidence to suggest that plant based diets may not deliver adequate nutrients to support optimal bone health, with some studies finding vegetarians and vegans to be at higher risk of fracture[11] and have lower bone mineral density[12] compared with omnivores. It is therefore important to carefully plan plant-based diets to deliver adequate nutrients that are supportive of bone health such as protein, calcium, Vitamin D, magnesium, potassium, zinc and Vitamin K and C.

Plant-based diets and the gut microbiome

Our understanding of the complex influence that plant-based diets have on the gut microbiome is still emerging. A plant-based diet is often rich in dietary fibre, including soluble and insoluble fibre, and resistant starch, as well as polyphenols.

The consumption of dietary fibre supports a high abundance of microbes that produce butyrate and other short-chain fatty acids which have an anti-inflammatory effect and strengthen the intestinal barrier function. In contrast, a low fibre diet has been found to be associated with a shift towards more mucus-degrading bacteria being present, compared with fibre-degrading bacteria[13].

The polyphenols in plant foods are metabolised into bioactive compounds and support the abundance of beneficial bacteria such as Lactobacillus and Bifidobacterium[14]. Some plant-based foods, e.g., nuts, have a prebiotic effect which also supports an increase in butyrate-producing and other beneficial microbes[15]. Interestingly, cross-sectional studies that compare vegans or vegetarians with non-vegetarians have not consistently found differences in gut microbial composition[16], leading the authors suggest that it is possible that microbial function is more important that microbial composition.

Plant-based diets across the life cycle

Well-planned plant-based diets can deliver adequate nutrition to meet requirements across all life stages. Demand for individual nutrients varies across life stages and as such, it can be helpful to pay special attention to an individual’s intake of specific nutrients at the different life stages. The authors identify these nutrients of concern, listed below, that require special attention to ensure a nutritionally adequate intake is achieved (*vegans at increased risk of deficiency):

• Pregnancy/Lactation: iron, zinc, vitamin B12* (vegetarian and vegans should include vitamin B12 fortified foods and/or supplement if indicated), iodine (150 ug supplement recommended for all pregnant/lactating women), and docosahexaenoic acid (DHA).
• Infants/Childhood/Adolescence: iron, zinc, vitamin B12* (infants should be supplemented if maternal B12 intake/status is inadequate and children/adolescents should be supplemented or include vitamin B12 fortified foods), iodine, calcium, vitamin D, docosahexaenoic acid (DHA), and for vegans, potentially protein also.
• Older adults: Calcium, vitamin B6*, vitamin D, vitamin B12* and potentially protein.

To learn more about nutrient requirements for different ages and genders, please refer to the National Health and Medical Research Council’s Nutrient Reference Values for Australia and New Zealand.

Conclusion

A well-planned plant-based diet, whether vegan or vegetarian, can be consumed safely for across all life stages and may be associated with some health benefits. To ensure nutritional safety certain nutrients, such as calcium, iron, vitamin B12, and vitamin D, etc. require targeted consideration to ensure adequacy is achieved and maintained.

– Anna Millichamp, APD, Senior Teaching Fellow, PhD Candidate, Bond University

Full paper

Craig, W. J., Mangels, A. R., Fresán, U., Marsh, K., Miles, F. L., Saunders, A. V., Haddad, E. H., Heskey, C. E., Johnston, P., Larson-Meyer, E., & Orlich, M. (2021). The Safe and Effective Use of Plant-Based Diets with Guidelines for Health Professionals. Nutrients, 13(11), 4144. https://doi.org/10.3390/nu13114144

Available here.

References

1. Craig, W.J., et al., The Safe and Effective Use of Plant-Based Diets with Guidelines for Health Professionals. Nutrients, 2021. 13(11): p. 4144.
2. Rizzo, N.S., et al., Vegetarian Dietary Patterns Are Associated With a Lower Risk of Metabolic Syndrome: The Adventist Health Study 2. Diabetes Care, 2011. 34(5): p. 1225-1227.
3. Matsumoto, S., et al., Association between vegetarian diets and cardiovascular risk factors in non-Hispanic white participants of the Adventist Health Study-2. Journal of Nutritional Science, 2019. 8: p. e6.
4. Bradbury, K., et al., Erratum: Serum concentrations of cholesterol, apolipoprotein AI and apolipoprotein B in a total of 1694 meat-eaters, fish-eaters, vegetarians and vegans. European Journal of Clinical Nutrition, 2015. 69(10): p. 1180-1180.
5. Shah, B., et al., Anti‐inflammatory effects of a vegan diet versus the American Heart Association–recommended diet in coronary artery disease trial. Journal of the American Heart Association, 2018. 7(23): p. e011367.
6. Barnard, N.D., et al., A Mediterranean Diet and Low-Fat Vegan Diet to Improve Body Weight and Cardiometabolic Risk Factors: A Randomized, Cross-over Trial. Journal of the American Nutrition Association, 2022. 41(2): p. 127-139.
7. Chen, Z., et al., Plant versus animal based diets and insulin resistance, prediabetes and type 2 diabetes: the Rotterdam Study. Eur J Epidemiol, 2018. 33(9): p. 883-893.
8. de Carvalho, G.B., et al., Effect of different dietary patterns on glycemic control in individuals with type 2 diabetes mellitus: a systematic review. Critical Reviews in Food Science and Nutrition, 2020. 60(12): p. 1999-2010.
9. Aune, D., et al., 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. International journal of epidemiology, 2017. 46(3): p. 1029-1056.
10. Wolk, A., Potential health hazards of eating red meat. Journal of internal medicine, 2017. 281(2): p. 106-122.
11. Tong, T.Y., et al., Vegetarian and vegan diets and risks of total and site-specific fractures: results from the prospective EPIC-Oxford study. BMC medicine, 2020. 18(1): p. 1-15.
12. Tucker, K.L., Vegetarian diets and bone status. The American journal of clinical nutrition, 2014. 100(suppl_1): p. 329S-335S.
13. Desai, M.S., et al., A dietary fiber-deprived gut microbiota degrades the colonic mucus barrier and enhances pathogen susceptibility. Cell, 2016. 167(5): p. 1339-1353. e21.
14. Corrêa, T.A.F., et al., The two-way polyphenols-microbiota interactions and their effects on obesity and related metabolic diseases. Frontiers in nutrition, 2019. 6: p. 188.
15. Muralidharan, J., et al., Plant-based fat, dietary patterns rich in vegetable fat and gut microbiota modulation. Frontiers in nutrition, 2019. 6: p. 157.
16. Wu, G.D., et al., Comparative metabolomics in vegans and omnivores reveal constraints on diet-dependent gut microbiota metabolite production. Gut, 2016. 65(1): p. 63-72.

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