Issue 138 plant based diets

NUTRITION MANAGEMENT

HOW HEALTHY ARE PLANT-BASED DIETS? Maeve Hanan UK Registered Dietitian Freelance Maeve works as a Freelance Dietitian and also runs the blog Dietetically Speaking.com, which promotes evidence-based nutrition and fights nutritional nonsense.

This article will examine the nutrition considerations and health impact of plant-based diets (PBDs), which are becoming increasingly popular.

A 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 1) and there are different reasons why people choose to follow these type of diets; ranging from perceived health benefits and food preferences, to environmental protection and animal welfare.

NUTRITIONAL CONSIDERATIONS

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PBDs tend to be low in saturated fat and high in fruit, vegetables, wholegrains, beans, pulses, soy products, nuts 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 exceeded.1 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.28 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 intakes.3 Furthermore, a number of studies have found that vegetarian children may have low levels of vitamin D and vitamin B12.4 It is also important to remember that the recommended daily amount of iron for vegetarians is 1.8 times higher than for non-vegetarians, as iron coming from plant sources (nonhaem iron) acts less efficiently in our body than iron from animal sources (haem iron).5 Overall, PBDs can be balanced and healthy as long as they include all-important nutrients.28 As PBDs are not automatically healthy, it is still important to include plenty of fruit,

Table 1: Different types of PBDs Name of diet

Diet description

Vegan

No animal products are consumed (i.e. no meat, poultry, fish, dairy, eggs or honey).

Other animal based products are also usually avoided like: leather and cosmetics which contain ingredients derived from animals.

Ovo-vegetarian

No meat, poultry, seafood or dairy - but eggs are consumed.

Lacto-vegetarian

No meat, poultry, seafood or eggs - but dairy is consumed.

Vegetarian (a.k.a. lacto-ovo vegetarian)

No meat, poultry or seafood - but eggs and dairy are consumed.

Pescatarian

No meat or poultry - but fish, seafood, eggs and dairy are consumed.

Flexitarian (a.k.a. semi or demi-vegetarian)

Mainly follow a vegetarian diet, but occasionally eat animal based products (e.g. a few times per week or when eating at a restaurant).

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NUTRITION MANAGEMENT vegetables and fibre; while limiting foods 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 HEALTH OUTCOMES

Studies have found that PBDs lead to lower 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 al9 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 cancer. However, there was

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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 cancer.9 A limited amount of conflicting evidence has found a lower risk of dementia among those who follow a PBD, but more evidence is needed to investigate this.10 For those with Type 2 diabetes, PBDs have been associated with improved glycaemic control.11 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 effecting 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, nonsmokers and physically active.14 Furthermore, a

. . . 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.

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 vegetables.16 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 profile.17 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 health.18 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 for 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 pescatarians 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 disorder.23 Well planned PBDs 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 infants.27 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 PBD, many of the benefits can be achieved by eating more plant-based products and less animal-based products; without avoiding animal-based products altogether.

Therefore, adopting a ‘flexitarian’ approach may provide a more realistic and balanced diet for many people. www.NHDmag.com October 2018 - Issue 138

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