Skip to main content Accessibility help
×
Home
Hostname: page-component-564cf476b6-qp9dn Total loading time: 0.919 Render date: 2021-06-20T20:54:48.881Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "metricsAbstractViews": false, "figures": true, "newCiteModal": false, "newCitedByModal": true, "newEcommerce": true }

Vegetarian diets, low-meat diets and health: a review

Published online by Cambridge University Press:  03 April 2012

Claire T McEvoy
Affiliation:
Centre for Public Health, Queen's University Belfast, Institute of Clinical Science B, 1st Floor, Grosvenor Road, Belfast BT12 6BJ, UK
Norman Temple
Affiliation:
Centre for Science, Athabasca University, Athabasca, Alberta, Canada
Jayne V Woodside
Affiliation:
Centre for Public Health, Queen's University Belfast, Institute of Clinical Science B, 1st Floor, Grosvenor Road, Belfast BT12 6BJ, UK
Corresponding
E-mail address:
Rights & Permissions[Opens in a new window]

Abstract

Objective

To review the epidemiological evidence for vegetarian diets, low-meat dietary patterns and their association with health status in adults.

Design

Published literature review focusing primarily on prospective studies and meta-analyses examining the association between vegetarian diets and health outcomes.

Results

Both vegetarian diets and prudent diets allowing small amounts of red meat are associated with reduced risk of diseases, particularly CHD and type 2 diabetes. There is limited evidence of an association between vegetarian diets and cancer prevention. Evidence linking red meat intake, particularly processed meat, and increased risk of CHD, cancer and type 2 diabetes is convincing and provides indirect support for consumption of a plant-based diet.

Conclusions

The health benefits of vegetarian diets are not unique. Prudent plant-based dietary patterns which also allow small intakes of red meat, fish and dairy products have demonstrated significant improvements in health status as well. At this time an optimal dietary intake for health status is unknown. Plant-based diets contain a host of food and nutrients known to have independent health benefits. While vegetarian diets have not shown any adverse effects on health, restrictive and monotonous vegetarian diets may result in nutrient deficiencies with deleterious effects on health. For this reason, appropriate advice is important to ensure a vegetarian diet is nutritionally adequate especially for vulnerable groups.

Type
Nutrition and health
Copyright
Copyright © The Authors 2012

Over the past 50 years, with the aim of preventing dietary deficiencies, public health authorities have published age- and gender-specific nutrient intake recommendations(1). While this represents what is considered an ‘adequate’ diet, there is a lack of consensus regarding ‘optimal’ dietary intake to reduce the risk of preventable diseases such as CVD, cancer and type 2 diabetes mellitus (T2DM)(Reference Sabaté2). In this regard, prospective and cross-sectional studies investigating vegetarian diets and health status provide valuable results. These studies include the Adventist Health Study(Reference Beeson, Mills and Phillips3), the Oxford Vegetarian Study(Reference Thorogood, Mann and Appleby4), the Health Food Shoppers study(Reference Burr and Sweetnam5) and the Heidelberg Study(Reference Frentzel-Beyme, Claude and Eilber6). Overall, vegetarians tend to be slimmer, appear to be in better health, with reduced risk of chronic diseases and greater longevity when compared with omnivores(Reference Willett7). While no reliable estimates for the proportion of vegetarians within populations exist, results of polls and surveys have reported a population prevalence of between 1 % and 10 % in the European Union, the USA and Canada(8, 9).

It is unclear whether established health benefits for vegetarians are attributable to (i) the absence of meat in the diet, (ii) the increased consumption of particular food component(s), (iii) the pattern of foods eaten within the vegetarian diet or (iv) other healthy lifestyle components often associated with vegetarianism. Additionally, restrictive vegetarian diets can be inadequate in terms of nutrient provision and may even be harmful for longer-term health.

The present review details the evidence linking vegetarian diets, low-meat dietary patterns and chronic disease prevention and discusses potential nutritional inadequacies of restrictive vegetarian diets and implications for optimum health status.

Methods

A wide literature search was conducted for the present narrative review using the Ovid MEDLINE (US National Library of Medicine, Bethesda, MD, USA) database for relevant publications up to and including 31 March 2011. The search terms used to identify relevant studies were: ‘vegetarian’, ‘vegan’, ‘plant-based diets’, ‘meat’, ‘cardiovascular disease’, ‘blood pressure’, ‘cholesterol’, ‘body weight’, ‘diabetes’, ‘cancer’ and ‘dietary patterns’. The primary search was limited to human studies published in the English language. This wide search yielded over 2500 potential articles. Titles and abstracts were screened, and full-text manuscripts were reviewed only if the title/abstract examined vegetarian diets, components of a vegetarian diet or red meat intake in relation to nutritional and/or health outcomes. Review articles, controlled trials and meta-analyses were included. These searches were supplemented with manual searches of reference lists within manuscripts. Approximately 250 full-text articles were reviewed and the most relevant of these (n 80) were included in the present overview of the subject area.

What is a vegetarian diet?

Vegetarian diets are often heterogeneous in composition, involving a wide range of dietary practices and individual dietary restriction(s). In practice, adopting a vegetarian dietary pattern is traditionally interpreted to mean an absence of meat(Reference Fraser10). Variations of vegetarian diet include lacto-vegetarians (includes dairy) and lacto-ovo-vegetarians (includes dairy and eggs). Vegan diets have further restrictions imposed and exclude all foods of animal origin. Additionally, vegetarian diets are characterised by high consumption of fruit, vegetables, legumes, nuts, grains and soya protein-food components, and each of these may independently be associated with positive health outcomes(11).

Vegetarian diets and prevention of chronic disease

CVD

A pooled analysis of five prospective cohort studies, involving approximately 76 000 subjects from the USA, the UK and Germany, over a mean follow-up period of 10·6 years, reported that vegetarians had a 24 % (95 % CI 6 %, 38 %) reduction in mortality from CHD compared with regular meat-eaters(Reference Key, Fraser and Thorogood12). Further characterisation of the vegetarian cohorts within that analysis found that the greatest reductions in CHD mortality (34 %) were observed in individuals eating fish but no meat and in lacto-ovo-vegetarians when compared with regular meat-eaters. Furthermore, occasional meat-eaters demonstrated a 20 % reduction in CHD when compared with regular meat-eaters. In that analysis, no significant differences were observed for stroke mortality or overall mortality between vegetarians and non-vegetarians(Reference Key, Fraser and Thorogood12). Recent independent analyses of mortality rates in British vegetarians (EPIC–Oxford, the Oxford arm of the European Investigation into Cancer and Nutrition (EPIC)) and German vegetarians found non-significant reductions in CHD mortality in vegetarians compared with omnivores(Reference Key, Appleby and Spencer13, Reference Chang-Claude, Hermann and Elber14) but no significant differences were observed for overall mortality rates between vegetarians and omnivores in these cohorts(Reference Key, Appleby and Spencer13, Reference Chang-Claude, Hermann and Elber14). One possible explanation may be that overall mortality was low in the cohort populations compared with the general Western population. It is unclear whether omnivores included in these cohorts are truly representative of the general population in terms of dietary intake and other lifestyle behaviours. The cohort populations recruited in prospective studies have comprised Seventh Day Adventists and other health-conscious populations, who tend to be healthier than the general population in a number of ways. In addition to a high prevalence of vegetarianism, these populations also report low consumption of tobacco and alcohol and possibly increased levels of physical activity, which have independent benefits for CVD risk(Reference Key, Fraser and Thorogood12, Reference Key, Appleby and Spencer13). Despite consideration of these potential confounders and significant heterogeneity between prospective studies, the current data provide evidence that a vegetarian diet and/or infrequent meat consumption significantly reduces the risk of CHD death. Much of the cardioprotective effect of vegetarian diets has been attributed to differences in observed BMI, cholesterol levels and blood pressure levels between vegetarians and omnivores(Reference Key, Appleby and Spencer13).

Serum total cholesterol (TC), LDL cholesterol (LDL-C) and TAG are significantly lower in vegetarians than omnivores in several studies(Reference Appleby, Thorogood and Mann15Reference Toohey, Harris and DeWitt17). One study in New Zealand Seventh Day Adventists observed no difference between lipid profiles of vegetarians and omnivores, although lipid profiles in each group were noted to be lower than in the general population(Reference Harman and Panell18). The lipid-lowering effects of vegetarian diets have been demonstrated in small randomised trials(Reference Cooper, Goldberg and Trevisan19, Reference Kestin, Rouse and Correll20). A recent review suggests that vegetarian and lacto-ovo-vegetarian diets are associated with reductions in TC and LDL-C of about 10–15 %, vegan diets of approximately 15–25 % and combination diets (vegetarian with added fibre, soya and nuts) of approximately 20–35 %(Reference Ferdowsian and Barnard21), suggesting that the lipid-lowering effects of vegetarian diets is dependent on the actual portfolio of dietary components consumed. Furthermore, it is estimated that risk of CHD is reduced by approximately 1 % for each 1 % reduction in LDL-C(Reference Grundy, Cleeman and Merz22). Therefore, the observed reduction in CHD mortality in vegetarian populations appears to be in accordance with the reported lipid-lowering effects of vegetarian and vegan diets.

The incidence of hypertension appears to be lower in vegetarian populations(Reference Fraser10). In a cohort of 11 004 men and women aged 20–78 years, Appleby et al.(Reference Appleby, Davey and Key23) showed differences in age-adjusted mean values between omnivores and vegans of −4·2 mmHg and −2·6 mmHg in systolic blood pressure and −2·8 mmHg and −1·7 mmHg in diastolic blood pressure, for men and women, respectively (P < 0·005). There was no significant difference in blood pressure measurements observed between omnivores and vegetarians. After controlling for various confounding variables, the authors concluded that much of the variation in blood pressure was attributable to differences in BMI, with vegan subjects tending to be leaner than the other dietary groups.

Vegetarians and particularly vegans have lower body weights than the general population with a low incidence of obesity(Reference Fraser10, Reference Davey, Spencer and Appleby24, Reference Key, Appleby and Rosell25). BMI is on average 1–2 kg/m2 less in vegetarians and vegans compared with age- and gender-matched non-vegetarians(Reference Spencer, Appleby and Davey26). In the Adventist Health Study, BMI increased as the frequency of consumption of meat increased in both men and women(Reference Fraser27). Furthermore, the EPIC–Oxford cohort consisting of approximately 22 000 individuals, followed up over a mean 5·3 years, demonstrated an average weight gain of 400 g/year overall. When the cohort was subdivided into omnivores, fish-eaters, vegans and vegetarians, there was significantly lower weight gain in vegans (P < 0·05) and fish-eaters (P < 0·001) but not in vegetarians when compared with omnivores(Reference Rosell, Appleby and Spencer28). A recent small randomised controlled trial demonstrated improved efficacy of a vegan diet in long-term weight loss in postmenopausal women compared with a conventional weight-loss diet after 1 year (−4·9 kg v. −1·8 kg; P = 0·02) and 2 years (−3·1 kg v. −0·8 kg; P = 0·022)(Reference Turner-McGrievy, Barnard and Scialli29).

Cancer

Scientific evidence investigating the relationship between cancer incidence and vegetarian diet is limited. Results of a pooled analysis of five prospective studies found no significant difference between vegetarians and non-vegetarians in mortality from common causes of cancer including lung, colon, stomach, breast and prostate cancers(Reference Key, Fraser and Thorogood12). Overall, epidemiological data suggest that cancer incidence is lower in vegetarians compared with non-vegetarians, although results are inconsistent(Reference Fraser27, Reference Key, Appleby and Spencer30, Reference Key, Appleby and Spencer31) and probably depend on cancer site. The largest prospective study of 34 192 Seventh Day Adventists suggested cancer of the colon (relative risk (RR)=1·88, 95 % CI 1·24, 2·87; P = 0·003) and prostate (RR = 1·54, 95 % CI 1·05, 2·26; P = 0·03) were significantly more likely in omnivores than in vegetarians(Reference Fraser27) although this was not confirmed in a recent pooled analysis from two UK populations(Reference Key, Appleby and Spencer30). The Adventist study showed no difference in breast cancer incidence (RR = 1·25, 95 % CI 0·87, 1·80; P = 0·22) between vegetarians and non-vegetarians(Reference Fraser27). However, results from the UK Women's Cohort Study suggested that women who did not eat any meat had a significantly lower risk for breast cancer than did women who were regular meat-eaters(Reference Taylor, Burley and Greenwood32). In that study a dose–response effect was demonstrated, with each increase of 50 g/d in red meat intake increasing breast cancer risk by 11 % (95 % CI 1·04, 1·18), even after adjustment for lifestyle confounders including menopausal status.

Type 2 diabetes mellitus

Epidemiological studies have supported the hypothesis that vegetarian diets protect against T2DM(Reference Jenkins, Kendall and Marchie33). The Seventh Day Adventist study reported a significantly reduced prevalence of diabetes in vegetarians compared with non-vegetarians(Reference Fraser10). Increased adherence to a vegetarian diet in the Adventist study demonstrated a reduced risk of developing T2DM in an incremental manner(Reference Tonstad, Butler and Yan34). Clinical dietary studies investigating the impact of vegetarian diets in diabetic patients have shown significant reductions in fasting blood sugar, cholesterol and TAG levels(Reference Barnard, Jung and Inkeles35Reference Barnard, Cohen and Jenkins37). However, the results are confounded by resulting significant weight loss in the intervention groups throughout the diet period, in addition to increased exercise and lifestyle modifications in some cases.

Are there specific dietary components in vegetarian diets protective against disease?

Vegetarian diets are characterised by greater consumption of fruit and vegetables containing a myriad of phytochemicals, dietary fibre and antioxidants which may offer protective metabolic advantages for both cancer and CVD risk. Fruit and/or vegetable intake may reduce cancer risk(Reference Boffetta, Couto and Wichmann3841). Consumption of fruit and vegetables has consistently been inversely associated with risk of CVD, and this has been confirmed by meta-analyses(Reference Dauchet, Amouyel and Hercberg42Reference He, Nowson and Lucas44). It is currently recommended that diets should include 400 g of total fruit and vegetables daily, which equates to 5 portions/d(Reference Key, Schatzkin and Willett40, 41). There is also evidence to suggest that high fruit and vegetable intakes may reduce the risk of developing T2DM(Reference Carter, Gray and Troughton45, Reference Liu, Serdula and Janket46).

Vegetarian diets tend to be low in SFA and rich in n-6 PUFA, which is shown to have favourable effects on blood lipid fractions(Reference Key, Appleby and Rosell25). When intake of SFA is replaced by PUFA, the risk of CHD is decreased(Reference Mozaffarian, Micha and Wallace47).

Nuts are consumed more frequently in vegetarian diets and are good sources of plant sterols, antioxidant vitamins and minerals, MUFA and dietary fibre. A review of epidemiological data reported a 37 % risk reduction in CHD death in adults consuming nuts more than four times weekly and 8·3 % risk reduction for each weekly serving of nuts(Reference Kelly and Sabaté48). A recent pooled analysis of twenty-five trials, involving 583 men and women with normal to increased untreated cholesterol levels, reported an average 5·1 % reduction in TC and 7·4 % reduction in LDL-C levels with a mean nut intake of 67 g/d(Reference Sabaté, Oda and Ros49).

Recent interest has focused on the role of foods and food components such as oats (β-glucans), psyllium, soya protein and plant sterols, which may be consumed in greater quantities in vegetarian diets. A meta-analysis involving forty-one randomised controlled trials found soya protein supplementation was associated with a significant reduction in mean TC, LDL-C and TAG and a significant increase in HDL cholesterol(Reference Reynolds, Chin and Lees50). The National Cholesterol Education Program Adult Treatment Panel III guidelines recommend increasing intake of plant sterols or stanols (2 g/d) to help achieve cholesterol treatment goals(Reference Patch, Tapsell and Williams51). Intake of 1–2 g plant sterols/d has been shown to reduce LDL-C by approximately 10–15 %(Reference Law52). Furthermore, soya protein contains phyto-oestrogens, specifically isoflavones, which may have a protective role in breast cancer development, especially in Asian women where soyabeans are a staple food(Reference Trock, Hilakivi-Clarke and Clarke53Reference Wu, Koh and Wang55). In Western women the main source of phyto-oestrogens are lignans, which may also have a protective role in breast cancer development. Recent meta-analyses reported that high levels of plant lignan intake are significantly associated with reduced breast cancer risk in postmenopausal women(Reference Velentzis, Cantwell and Cardwell56, Reference Buck, Zaineddin and Vrieling57).

Reduced meat intake, dietary patterns and protection against disease

The health benefits of vegetarian diets are not necessarily unique. As outlined previously, modest fish and dairy consumption as well as occasional meat intake have also been associated with reduced risk of CHD when compared with regular meat-eaters. In addition, there are inconsistencies in results, particularly for cancer risk in vegetarian and omnivore cohorts, despite convincing evidence linking red meat consumption and cancer risk (discussed later). It appears that populations with small intakes of total meat can also experience health benefits when compared with the general population. In this regard, the dietary patterns approach in nutritional epidemiology provides further evidence that adherence to prudent diets such as the Mediterranean diet and the DASH (Dietary Approaches to Stop Hypertension) diet is associated with significant improvements in health status. These prudent diets are characterised by increased consumption of plant foods, low SFA intake, high dietary fibre intake and low intakes of refined carbohydrate. However, in contrast to vegetarian diets, these prudent dietary patterns also allow consumption of small amounts of red meat in addition to fish and dairy products.

Adherence to a Mediterranean diet has been associated with longevity in a number of large epidemiological studies(Reference Knoops, de Groot and Kromhout58Reference Trichopoulou, Costacou and Bamia60). A meta-analysis of these studies included more than 1·5 million healthy subjects and 40 000 fatal and non-fatal events(Reference Sofi, Cesari and Abbate61). The authors concluded that greater adherence to a Mediterranean diet is significantly associated with a reduced risk of overall mortality, CVD mortality and cancer incidence and mortality.

In the Lyon Diet Heart Study, a secondary prevention randomised controlled trial with free-living subjects recently diagnosed with a CHD event, those in the Mediterranean diet intervention group had a 50–70 % reduction of recurrent CHD including cardiac death(Reference de Lorgeril, Salen and Martin62). Trichopoulou et al.(Reference Trichopoulou, Costacou and Bamia60) assessed the effects of Mediterranean diet score on survival; there were no strong associations seen for each of the individual dietary components of the Mediterranean diet score, suggesting that it is the overall pattern that is protective. Evidence from the DASH study suggests that the DASH diet has a significant lowering effect on blood pressure, independent of body weight and Na intake, in both hypertensive and normotensive adults(Reference Appel, Moore and Obarzanek63, Reference Appel64). A recent prospective study evaluated the association between a DASH-style diet adherence score and CHD risk in women(Reference Fung, Chiuve and McCullough65). Diet was assessed seven times during 24 years of follow-up. Women with a high DASH score had a lower risk of CHD: those in the top quintile of the DASH score had an RR of 0·76, compared with those in the bottom quintile (P < 0·001 for trend).

Is an absence of red meat protective against disease?

Components of vegetarian diets are not always clearly defined across studies. While emphasis is on increased consumption of plant foods, the actual dietary quality in terms of nutrient intake can be variable. The only known constant in a vegetarian diet is the absence of red meat. Therefore, evidence linking red meat and health status can be valuable when considering the overall potential effects of vegetarian diets and health.

Red and processed meat intake has been positively associated with CVD, T2DM and certain cancers in epidemiological studies(Reference Sinha, Cross and Graubard66, Reference Micha, Wallace and Mozaffarian67). The NIH (National Institutes of Health)–AARP (formerly known as the American Association of Retired Persons) prospective study from the USA, involving over half a million adults aged 50–71 years over 10 years, found increased risk of total mortality and CVD mortality among those in the highest quintile of red meat and processed meat intake, compared with those in the lowest quintile(Reference Sinha, Cross and Graubard66). However, individuals in the highest quintile of meat intake were also more likely to have higher BMI, increased smoking and sedentary lifestyles. These lifestyle factors are inherently difficult to measure, so the effects of residual confounding may not have been fully accounted for in the overall analysis. A recent large systematic review and meta-analysis involving twenty studies, including Sinha et al.(Reference Sinha, Cross and Graubard66), found no significant association between red meat intake and incident CHD, but did find that consumption of processed meats was associated with a 42 % higher CHD risk for each 50 g/d increase in intake(Reference Micha, Wallace and Mozaffarian67).

The second report published by the World Cancer Research Fund/American Institute for Cancer Research(41) found meat consumption to be the only convincing dietary factor associated with increased risk of colon cancer. Even so, colon cancer incidence rates in vegetarian populations compared with omnivores are not consistent between UK and US prospective studies as mentioned previously(Reference Fraser10).

Additionally, a recent systematic review, involving seven prospective cohorts, concluded that processed meat consumption of 50 g/d is associated with a 19 % higher risk of diabetes, while consumption of unprocessed red meat is associated with a non-significant trend towards a higher risk of diabetes(Reference Micha, Wallace and Mozaffarian67).

Nutritional adequacy of vegetarian diets

Carefully planned vegetarian and vegan diets can provide adequate nutrients for optimum health(11). Evidence suggests that infants and children can be successfully reared on vegan and vegetarian diets(Reference Mangels and Messina68, Reference Messina and Mangels69). However, all dietary practices, including non-vegetarian diets, can be deleterious for health if essential nutrients are not consumed according to an individual's needs. Therefore, vegetarian and vegan diets need to ensure a balance of nutrients from a wide variety of foods, especially for vulnerable groups such as pregnant or lactating women and children. Nutrients most likely to be deficient in unbalanced or very restrictive vegetarian diets are Fe, vitamin D, vitamin B12 and n-3 fatty acids.

Fe

Fe deficiency occurs as a result of inadequate intake and/or poor bioavailability from the diet. An adequate intake of Fe in vegetarians and vegans has been demonstrated but the incidence of Fe-deficiency anaemia is no greater in vegetarians than in omnivores although Fe stores tend to be lower, especially in women(Reference Hunt70). It is recommended that Fe intakes be higher in vegetarians and vegans(11), as plant sources of Fe (non-haem) are less bioavailable. Furthermore, phytate, soya protein and polyphenols/tannin within a plant-based diet can inhibit Fe absorption further. Ascorbic acid, retinol, alcohol and carotenes can enhance the absorption of non-haem Fe(Reference Hunt70).

Vitamin B12 (cobalamin)

Vitamin B12 is required by the body only in small amounts but is almost completely restricted to foods of animal origin. Deficiency of vitamin B12 can cause pernicious anaemia and can result in megaloblastic anaemia with central nervous system demyelination if not treated early(Reference Stabler and Allen71). The difficulty in diagnosing vitamin B12 deficiency prior to symptom development in vegetarians can be due to a high folic acid intake: this can mask the haematological signs of deficiency. Since folate intake is often higher in vegan diets, elevated serum methylmalonic acid, holo-transcobalamin and/or homocysteine may be more sensitive indicators of a vitamin B12 deficiency(Reference Stabler and Allen71). Several studies have consistently reported lower vitamin B12 status and higher homocysteine levels in vegetarians, particularly vegans, when compared with omnivores(Reference Huang, Chang and Chiu72, Reference Yajnik, Deshpande and Lubree73). Purported plant-based sources (tempeh, algae extracts and sea vegetables) have been found to contain more inactive corrinoids than true vitamin B12(Reference Stabler and Allen71) and thus they are not reliable sources of B12. Risk of vitamin B12 deficiency in vegans is increased if the diet is not supplemented with fortified products (fortified yeast extract, fortified soya products and breakfast cereals).

Vitamin D

Dietary sources of vitamin D include oily fish, fortified margarines and breakfast cereals. Vegan and very restrictive vegetarian diets pose risk of deficiency, particularly among those living in northern latitudes where there is less opportunity for sunlight exposure. Lower serum 25-hydroxyvitamin D levels have been reported in vegetarians and vegans compared with omnivores(Reference Crowe, Steur and Allen74). Emerging evidence suggests a role for optimal vitamin D status in disease prevention including CVD, cancer and T2DM(Reference Autier and Gandini75Reference Trump, Deeb and Johnson77), therefore maintaining adequate status is important. Dietary sources include fortified soya milks and cheeses and margarines. In some cases a vitamin D supplement may be required(11).

n-3 Fatty Acids

n-3 Fatty acids are thought to be important for immune, cognitive and cardiac function. Vegetarian diets may be lower in n-3 fatty acids, in particular the marine fatty acids EPA and DHA, and higher in n-6 fatty acids (linoleic acid)(11). Plant derived α-linolenic acid can be converted to EPA and DHA in vivo, but the rate of conversion is low(Reference Pawlosky, Hibbeln and Novotny78). Consequently, lower serum levels of EPA and DHA have been reported in vegans(Reference Craig79, Reference Sanders80) as well as lower erythrocyte phospholipids n-3 status in vegans and vegetarians(Reference Kornsteiner, Singer and Elmadfa81). The health effects of lower marine n-3 fatty acid status are not known at this time(Reference Sanders80). Vegan sources of n-3 fatty acids include flaxseed and flaxseed oil, canola oil, olive oil and/or vegan DHA supplement(11).

Conclusions

Vegetarian diets are associated with reduced risk of CHD and T2DM in health-conscious individuals. At present, there is limited evidence of a beneficial effect of vegetarianism in reducing risk of cancer and further studies are warranted. A major problem with recommending vegetarian diets for improved health is that a vegetarian diet is inadequately defined in terms of nutrient and food content. The only certain aspect of a vegetarian diet, by definition, is the absence of red meat. Other prudent dietary patterns allowing small amounts of lean red meat appear to offer significant protection against CVD, cancer and overall mortality. Findings from cohort studies to date indicate that increased meat consumption, especially processed meat, is positively and strongly associated with incident CHD, T2DM, perhaps colon cancer and all-cause mortality, independent of other lifestyle factors.

At this time, it is unclear whether the absence of meat and meat products from the vegetarian diet, or whether differences in type and variety of foods replaced when meat is infrequently consumed, explains the observed reduction in mortality from CHD in vegetarian cohorts. Additionally, it is not known whether a particular food, dietary compound or a combination of dietary or lifestyle/behavioural factors in the vegetarian diet provides optimal protection against chronic disease development.

It is recognised that over-reliance on one single food, or food group, will not provide the range of nutrients required for optimum health and well-being. This is the case for all diets – omnivorous, vegetarian or vegan. Regardless of the degree of vegetarianism, exclusion of major food groups from the diet is likely to result in nutrient deficiencies, particularly for vulnerable groups such as infants, menstruating women and pregnant or lactating women.

In conclusion, based on available evidence to date, all dietary practices should aim to meet current nutritional guidelines to reduce risk of chronic disease development(82). A diet low in SFA, refined sugar, processed meat and salt, and rich in fruit and vegetables and dietary fibre, is recommended. Moderation and variety in individual diets is also important. Vegetarian dietary patterns need to be adequately defined and further intervention trials are required before they can be widely advocated for optimal health status.

Acknowledgements

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. There are no conflicts of interest to declare. Each named author (C.T.M., N.T. and J.V.W.) made a substantial contribution to the literature review, drafting and final preparation of this manuscript.

References

1.Committee on Medical Aspects of Nutrition and Food Policy, Department of Health (1991) Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Report on Health and Social Subjects no. 41. London: HMSO.Google Scholar
2.Sabaté, J (2003) The contribution of vegetarian diets to human health. Forum Nutr 56, 218220.Google ScholarPubMed
3.Beeson, WL, Mills, PK, Phillips, RLet al. (1989) Chronic disease among Seventh-day Adventists, a low-risk group. Rationale, methodology, and description of the population. Cancer 64, 570581.3.0.CO;2-4>CrossRefGoogle ScholarPubMed
4.Thorogood, M, Mann, J, Appleby, Pet al. (1994) Risk of death from cancer and ischaemic heart disease in meat and non-meat eaters. BMJ 308, 16671671.CrossRefGoogle ScholarPubMed
5.Burr, ML & Sweetnam, PM (1982) Vegetarianism, dietary fiber, and mortality. Am J Clin Nutr 36, 873877.CrossRefGoogle ScholarPubMed
6.Frentzel-Beyme, R, Claude, J & Eilber, U (1988) Mortality among German vegetarians: first results after 5 years of follow up. Nutr Cancer 11, 117126.CrossRefGoogle Scholar
7.Willett, WC (1999) Convergence of philosophy and science: the Third International Congress on Vegetarian Nutrition. Am J Clin Nutr 70, 3 Suppl., 434S438S.CrossRefGoogle ScholarPubMed
8.European Vegetarian Union (2007) How many Veggies…? http://www.european-vegetarian.org/lang/en/info/howmany.php (accessed January 2009).Google Scholar
9.Food Standards Agency UK (2002) The National Diet & Nutrition Survey: adults aged 19 to 64 years. Types and quantities of foods consumed. http://www.food.gov.uk/multimedia/pdfs/ndnsprintedreport.pdf (accessed March 2011).Google Scholar
10.Fraser, GE (2009) Vegetarian diets: what do we know of their effects on common chronic diseases? Am J Clin Nutr 89, issue 5, 1607S1612S.CrossRefGoogle ScholarPubMed
11.American Dietetic Association (2009) Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc 109, 12661282.CrossRefGoogle Scholar
12.Key, TJ, Fraser, GE, Thorogood, Met al. (1999) Mortality in vegetarians and non-vegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J Clin Nutr 70, Suppl. 3, 516S524S.CrossRefGoogle Scholar
13.Key, TJ, Appleby, PN, Spencer, EAet al. (2009) Mortality in British vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC–Oxford). Am J Clin Nutr 89, issue 5, 1613S1619S.CrossRefGoogle Scholar
14.Chang-Claude, J, Hermann, S, Elber, Uet al. (2005) Lifestyle determinants and mortality in German vegetarians and health conscious persons: results of a 21 year follow up. Cancer Epidemol Biomarkers Prev 14, 963968.CrossRefGoogle ScholarPubMed
15.Appleby, PN, Thorogood, M, Mann, JLet al. (1999) The Oxford Vegetarian Study: an overview. Am J Clin Nutr 70, Suppl. 3, 525S531S.CrossRefGoogle ScholarPubMed
16.De Baise, SG, Fernandes, SFC, Gianni, RJet al. (2007) Vegetarian diet and cholesterol and triglyceride levels. Arq Bras Cardiol 88, 3236.Google Scholar
17.Toohey, ML, Harris, MA, DeWitt, Wet al. (1998) Cardiovascular disease risk factors are lower in African-American vegans compared to lacto-ovo-vegetarians. J Am Coll Nutr 17, 425434.CrossRefGoogle ScholarPubMed
18.Harman, SK & Panell, WR (1998) The nutritional health of New Zealand vegetarian and non-vegetarian Seventh-day Adventists: selected vitamin, mineral and lipid levels. N Z Med J 111, 9194.Google ScholarPubMed
19.Cooper, RS, Goldberg, RB, Trevisan, Met al. (1982) The selective lipid-lowering effect of vegetarianism on low density lipoproteins in a cross-over experiment. Atherosclerosis 44, 293305.CrossRefGoogle Scholar
20.Kestin, M, Rouse, IL, Correll, RAet al. (1989) Cardiovascular disease risk factors in free-living men: comparison of two prudent diets, one based on lacto-ovo-vegetarianism and the other allowing lean meat. Am J Clin Nutr 50, 280287.CrossRefGoogle Scholar
21.Ferdowsian, HR & Barnard, ND (2009) Effects of plant-based diets on plasma lipids. Am J Cardiol 104, 947956.CrossRefGoogle ScholarPubMed
22.Grundy, SM, Cleeman, JI, Merz, CNet al. (2004) Implications of recent clinical trials for the National Cholesterol Education Program Adult Treatment Panel III guidelines. Circulation 110, 227239.CrossRefGoogle ScholarPubMed
23.Appleby, PN, Davey, GK & Key, TJ (2002) Hypertension and blood pressure among meat eaters, fish eaters, vegetarians and vegans in EPIC–Oxford. Public Health Nutr 5, 645654.CrossRefGoogle ScholarPubMed
24.Davey, GK, Spencer, EA, Appleby, PNet al. (2003) EPIC–Oxford: lifestyle characteristics and nutrient intakes in a cohort of 33 883 meat-eaters and 31 546 non meat-eaters in the UK. Public Health Nutr 6, 259269.CrossRefGoogle Scholar
25.Key, TJ, Appleby, PN & Rosell, MS (2006) Health effects of vegetarian and vegan diets. Proc Nutr Soc 65, 3541.CrossRefGoogle ScholarPubMed
26.Spencer, EA, Appleby, PN, Davey, GKet al. (2003) Diet and body mass index in 38,000 EPIC–Oxford meat eaters, fish eaters, vegetarians and vegans. Int J Obes Relat Metab Disord 27, 728734.CrossRefGoogle Scholar
27.Fraser, GE (1999) Associations between diet and cancer, ischemic heart disease, and all cause mortality in non-Hispanic white California Seventh-day Adventists. Am J Clin Nutr 70, Suppl. 3, 532S538S.CrossRefGoogle ScholarPubMed
28.Rosell, M, Appleby, PN, Spencer, EAet al. (2006) Weight gain over 5 years in 21,966 meat-eating, fish-eating, vegetarian, and vegan men and women in EPIC–Oxford. Int J Obes (Lond) 30, 13891396.CrossRefGoogle ScholarPubMed
29.Turner-McGrievy, GM, Barnard, ND & Scialli, AR (2007) A two-year randomized weight loss trial comparing a vegan diet to a more moderate low-fat diet. Obesity (Silver Spring) 15, 22762281.CrossRefGoogle ScholarPubMed
30.Key, TJ, Appleby, PN, Spencer, EAet al. (2009) Cancer incidence in British vegetarians. Br J Cancer 101, 192197.CrossRefGoogle ScholarPubMed
31.Key, TJ, Appleby, PN, Spencer, EAet al. (2009) Cancer incidence in vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC–Oxford). Am J Clin Nutr 89, issue 5, 1620S1626S.CrossRefGoogle Scholar
32.Taylor, EF, Burley, VJ, Greenwood, DCet al. (2007) Meat consumption and risk of breast cancer in the UK Women's Cohort Study. Br J Cancer 96, 11391146.CrossRefGoogle ScholarPubMed
33.Jenkins, DJ, Kendall, CW, Marchie, Aet al. (2003) Type 2 diabetes and the vegetarian diet. Am J Clin Nutr 78, 3 Suppl., 610S616S.CrossRefGoogle ScholarPubMed
34.Tonstad, S, Butler, T, Yan, Ret al. (2009) Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care 32, 791796.CrossRefGoogle ScholarPubMed
35.Barnard, RJ, Jung, T & Inkeles, SB (1994) Diet and exercise in the treatment of NIDDM: the need for early emphasis. Diabetes Care 17, 14691472.CrossRefGoogle ScholarPubMed
36.Crane, MG & Sample, C (1994) Regression of diabetic neuropathy with total vegetarian (vegan) diet. J Nutr Med 4, 431439.Google Scholar
37.Barnard, ND, Cohen, J, Jenkins, DJet al. (2009) A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: a randomized, controlled, 74-wk clinical trial. Am J Clin Nutr 89, issue 5, 1588S1596S.CrossRefGoogle Scholar
38.Boffetta, P, Couto, E, Wichmann, Jet al. (2010) Fruit and vegetable intake and overall cancer risk in the European Prospective Investigation into Cancer and Nutrition (EPIC). J Natl Cancer Inst 102, 529537.CrossRefGoogle Scholar
39.Gonzalez, CA & Riboli, E (2006) Diet and cancer prevention: where we are, where we are going. Nutr Cancer 56, 225231.CrossRefGoogle ScholarPubMed
40.Key, TJ, Schatzkin, A, Willett, WCet al. (2004) Diet, nutrition and the prevention of cancer. Public Health Nutr 7, 187200.CrossRefGoogle ScholarPubMed
41.World Cancer Research Fund/American Institute Cancer Research Expert Report (2007) Food, Nutrition, Physical Activity and the Prevention of Cancer: A Global Perspective. Washington, DC: AICR.Google Scholar
42.Dauchet, L, Amouyel, P, Hercberg, Set al. (2006) Fruit and vegetable consumption and risk of coronary heart disease: a meta-analysis of cohort studies. J Nutr 136, 25882593.CrossRefGoogle ScholarPubMed
43.He, FJ, Nowson, CA & MacGregor, GA (2006) Fruit and vegetable consumption and stroke: meta-analysis of cohort studies. Lancet 367, 320326.CrossRefGoogle ScholarPubMed
44.He, FJ, Nowson, CA, Lucas, Met al. (2007) Increased consumption of fruit and vegetables is related to a reduced risk of coronary heart disease: meta-analysis of cohort studies. J Hum Hypertens 21, 717728.CrossRefGoogle ScholarPubMed
45.Carter, P, Gray, LJ, Troughton, Jet al. (2010) Fruit and vegetable intake and incidence of type 2 diabetes mellitus: systematic review and meta-analysis. BMJ 341, c4229.CrossRefGoogle ScholarPubMed
46.Liu, S, Serdula, M, Janket, SJet al (2004) A prospective study of fruit and vegetable intake and the risk of type 2 diabetes in women. Diabetes Care 27, 29932996.CrossRefGoogle ScholarPubMed
47.Mozaffarian, D, Micha, R & Wallace, S (2010) Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med 7, e1000252.CrossRefGoogle ScholarPubMed
48.Kelly, JH Jr & Sabaté, J (2006) Nuts and coronary heart disease: an epidemiological perspective. Br J Nutr 96, Suppl. 2, S61S67.CrossRefGoogle Scholar
49.Sabaté, J, Oda, K & Ros, E (2010) Nut consumption and blood lipid levels: a pooled analysis of 25 intervention trials. Arch Intern Med 170, 821827.CrossRefGoogle ScholarPubMed
50.Reynolds, K, Chin, A, Lees, KAet al. (2006) A meta-analysis of the effect of soy protein supplementation on serum lipids. Am J Cardiol 98, 633640.CrossRefGoogle ScholarPubMed
51.Patch, CS, Tapsell, LC & Williams, PG (2005) Plant sterol/stanol prescription is an effective treatment strategy for managing hypercholesterolemia in outpatient clinical practice. J Am Diet Assoc 105, 4652.CrossRefGoogle ScholarPubMed
52.Law, M (2000) Plant sterol and stanol margarines and health. BMJ 320, 861864.CrossRefGoogle ScholarPubMed
53.Trock, BJ, Hilakivi-Clarke, L & Clarke, R (2006) Meta-analysis of soy intake and breast cancer risk. J Natl Cancer Inst 98, 459471.CrossRefGoogle ScholarPubMed
54.Qin, LQ, Xu, JY, Wang, PYet al. (2006) Soyfood intake in the prevention of breast cancer risk in women: a meta-analysis of observational epidemiological studies. J Nutr Sci Vitaminol (Tokyo) 52, 428436.CrossRefGoogle ScholarPubMed
55.Wu, AH, Koh, WP, Wang, Ret al. (2008) Soy intake and breast cancer risk in Singapore Chinese Health Study. Br J Cancer 99, 196200.CrossRefGoogle ScholarPubMed
56.Velentzis, LS, Cantwell, MM, Cardwell, Cet al. (2009) Lignans and breast cancer risk in pre- and post-menopausal women: meta-analyses of observational studies. Br J Cancer 100, 14921498.CrossRefGoogle ScholarPubMed
57.Buck, K, Zaineddin, AK, Vrieling, Aet al. (2010) Meta-analyses of lignans and enterolignans in relation to breast cancer risk. Am J Clin Nutr 92, 141153.CrossRefGoogle ScholarPubMed
58.Knoops, KT, de Groot, LC, Kromhout, Det al. (2004) Mediterranean diet, lifestyle factors, and 10-year mortality in elderly European men and women: the HALE project. JAMA 292, 14331439.CrossRefGoogle ScholarPubMed
59.Mitrou, PN, Kipnis, V, Thiébaut, ACet al. (2007) Mediterranean dietary pattern and prediction of all-cause mortality in a US population: results from the NIH–AARP Diet and Health Study. Arch Intern Med 167, 24612468.CrossRefGoogle Scholar
60.Trichopoulou, A, Costacou, T, Bamia, Cet al. (2003) Adherence to a Mediterranean diet and survival in a Greek population. New Engl J Med 348, 25992608.CrossRefGoogle Scholar
61.Sofi, F, Cesari, F, Abbate, Ret al. (2008) Adherence to Mediterranean diet and health status: meta-analysis. BMJ 337, a1344.CrossRefGoogle ScholarPubMed
62.de Lorgeril, M, Salen, P, Martin, JLet al. (1999) Mediterranean diet, traditional risk factors, and the rate of cardiovascular complications after myocardial infarction: final report of the Lyon Diet Heart Study. Circulation 99, 779785.CrossRefGoogle ScholarPubMed
63.Appel, LJ, Moore, TJ, Obarzanek, Eet al. (1997) A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med 336, 11171124.CrossRefGoogle ScholarPubMed
64.Appel, LJ (2003) Lifestyle modification as a means to prevent and treat high blood pressure. J Am Soc Nephrol 14, Suppl. 2, S99S102.CrossRefGoogle ScholarPubMed
65.Fung, TT, Chiuve, SE, McCullough, MLet al. (2008) Adherence to a DASH-style diet and risk of coronary heart disease and stroke in women. Arch Intern Med 168, 713720.CrossRefGoogle ScholarPubMed
66.Sinha, R, Cross, AJ, Graubard, BIet al. (2009) Meat intake and mortality: a prospective study of over half a million people. Arch Intern Med 169, 562571.CrossRefGoogle ScholarPubMed
67.Micha, R, Wallace, SK & Mozaffarian, D (2010) Red and processed meat consumption and risk of incident coronary heart disease, stroke, and diabetes mellitus: a systematic review and meta-analysis. Circulation 121, 22712283.CrossRefGoogle ScholarPubMed
68.Mangels, AR & Messina, V (2001) Considerations in planning vegan diets: infants. J Am Diet Assoc 101, 670677.CrossRefGoogle ScholarPubMed
69.Messina, V & Mangels, AR (2001) Considerations in planning vegan diets: children. J Am Diet Assoc 101, 661669.CrossRefGoogle ScholarPubMed
70.Hunt, J (2003) Bioavailability of iron, zinc and other trace minerals from vegetarian diets. Am J Clin Nutr 78, 3 Suppl., 633S639S.CrossRefGoogle ScholarPubMed
71.Stabler, SP & Allen, RH (2004) Vitamin B12 deficiency as a worldwide problem. Annu Rev Nutr 24, 299326.CrossRefGoogle ScholarPubMed
72.Huang, YC, Chang, SJ, Chiu, YTet al. (2003) The status of plasma homocysteine and related B-vitamins in healthy young vegetarians and nonvegetarians. Eur J Nutr 42, 8490.CrossRefGoogle ScholarPubMed
73.Yajnik, CS, Deshpande, SS, Lubree, HGet al. (2006) Vitamin B12 deficiency and hyperhomocysteinemia in rural and urban Indians. J Assoc Physicians India 54, 775782.Google ScholarPubMed
74.Crowe, FL, Steur, M, Allen, NEet al. (2011) Plasma concentrations of 25-hydroxyvitamin D in meat eaters, fish eaters, vegetarians and vegans: results from the EPIC–Oxford study. Public Health Nutr 14, 340346.CrossRefGoogle ScholarPubMed
75.Autier, P & Gandini, S (2007) Vitamin D supplementation and total mortality: a meta-analysis of randomized controlled trials. Arch Intern Med 167, 17301737.CrossRefGoogle ScholarPubMed
76.Giovannucci, E, Liu, Y & Willett, WC (2006) Cancer incidence and mortality and vitamin D in black and white male health professionals. Cancer Epidemiol Biomarkers Prev 15, 24672472.CrossRefGoogle ScholarPubMed
77.Trump, DL, Deeb, KK & Johnson, CS (2010) Vitamin D: considerations in the continued development as an agent for cancer prevention and therapy. Cancer J 16, 19.CrossRefGoogle ScholarPubMed
78.Pawlosky, RJ, Hibbeln, JR, Novotny, JAet al. (2001) Physiological compartmental analysis of α-linolenic acid metabolism in adult humans. J Lipid Res 42, 12571265.Google ScholarPubMed
79.Craig, WJ (2009) Health effects of vegan diets. Am J Clin Nutr 89, issue 5, 1627S1633S.CrossRefGoogle ScholarPubMed
80.Sanders, TAB (2009) DHA status of vegetarians. Prostaglandins Leukot Essent Fatty Acids 81, 137141.CrossRefGoogle ScholarPubMed
81.Kornsteiner, M, Singer, I & Elmadfa, I (2008) Very low n-3 long-chain polyunsaturated fatty acid status in Austrian vegetarians and vegans. Ann Nutr Metab 52, 3747.CrossRefGoogle ScholarPubMed
82.World Health Organization (2003) Diet, Nutrition and the Prevention of Chronic Diseases: Joint WHO/FAO Expert Consultation. WHO Technical Report Series no. 916. Geneva: WHO.Google Scholar
You have Access
148
Cited by

Send article to Kindle

To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Vegetarian diets, low-meat diets and health: a review
Available formats
×

Send article to Dropbox

To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

Vegetarian diets, low-meat diets and health: a review
Available formats
×

Send article to Google Drive

To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

Vegetarian diets, low-meat diets and health: a review
Available formats
×
×

Reply to: Submit a response

Please enter your response.

Your details

Please enter a valid email address.

Conflicting interests

Do you have any conflicting interests? *