Elsevier

Nutrition

Volume 16, Issue 2, February 2000, Pages 111-119
Nutrition

Applied Nutritional Investigations
Antioxidant status in vegetarians versus omnivores

https://doi.org/10.1016/S0899-9007(99)00267-1Get rights and content

Abstract

Every day, vegetarians consume many carbohydrate-rich plant foods such as fruits and vegetables, cereals, pulses, and nuts. As a consequense, their diet contains more antioxidant vitamins (vitamin C, vitamin E, and β-carotene) and copper than that of omnivores. Intake of zinc is generally comparable to that by omnivores. However, the bioavailability of zinc in vegetarian diets is generally lower than that of omnivores. Dietary intake of selenium is variable in both groups and depends on the selenium content of the soil. Measurements of antioxidant body levels in vegetarians show that a vegetarian diet maintains higher antioxidant vitamin status (vitamin C, vitamin E, β-carotene) but variable antioxidant trace element status as compared with an omnivorous diet. To evaluate the antioxidative potential of a vegetarian diet versus an omnivorous diet, more studies are needed in which the total antioxidant capacity is determined rather than the status of a single antioxidant nutrient.

Introduction

The antioxidant defense system of the body consists of endogenous and exogenous antioxidants that work together at the molecular level to protect cell membranes, lipoproteins, and DNA from the damaging effects of free oxygen radicals.1 Endogenous antioxidants are enzymes that are primarily physiologic in origin; exogenous antioxidants include nutrients and non-nutrients that enter the body through the diet.

The most common dietary antioxidants and their sources and functions are shown in Table I. Dietary antioxidants can be divided into three groups based on the mechanisms of their actions: 1) vitamins and provitamins, such as vitamin C (ascorbic acid), vitamin E (α-tocopherol), and β-carotene, which react directly with free radicals or quench reactive oxygen species; 2) vitamins that are coenzymes of antioxidant regenerating enzymes (e.g., vitamin B1, vitamin B2, vitamin B6, vitamin B12, and niacin); and 3) minerals, which are structural components of antioxidant enzymes (copper and zinc in cytosolic superoxide dismutase, manganese in mitochondrial superoxide dismutase, and selenium in glutathione peroxidase).2 In addition to these antioxidant nutrients, the diet provides a larger group of non-nutrients with antioxidant activity (polyphenols, glucosinolates, indoles, etc.).3

Assessments of antioxidant status are generally based on the concentrations of antioxidant vitamins and minerals in the blood or other tissues such as hair, nails, etc. The status of antioxidant minerals (zinc, copper, and selenium) can also be estimated on the basis of the activities of enzymes dependent on these minerals, e.g., zinc- and copper-dependent superoxide dismutase in plasma and erythrocytes and selenium-dependent glutathione peroxidase in plasma.4

Antioxidants play a significant role in the pathogenesis of a number of age-related diseases (Table I). Epidemiological data strongly support the belief that high consumption of fruits and vegetables protects against degenerative diseases such as cancer5, 6 and ischemic heart disease.7 However, several cohort studies7 and large-scale clinical trials8 have failed to show the protective effect of a single antioxidant. Hence, the recently published guideline by the World Cancer Research Fund and the American Institute for Cancer Research6 proposes that, to reduce the risk of cancer, one should follow a varied diet based primarily on foods of plant origin.

In this article, the question of whether vegetarians are better protected than omnivores against free radical ions is approached by examining those studies in which the status of antioxidant nutrients has been measured in vegetarians. However, most studies on antioxidant vitamins have reported only dietary data and not biochemical data, but this paucity of information does not apply to antioxidant trace elements.9 Therefore, this article reviews primarily those studies on dietary intake and body status of the most common antioxidant vitamins (vitamin C, vitamin E, β-carotene) in vegetarians and omnivores and only those studies on antioxidant trace element status (zinc, copper, and selenium) in vegetarians and omnivores that have been published since the review by Gibson.9 Furthermore, because a vegetarian diet can be composed in many different ways, a short description of the grouping of vegetarians is also provided.

Section snippets

Grouping of vegetarians

The principal difference among various vegetarian diets is the extent to which animal products are avoided, the vegan diet being the most restrictive and the semivegetarian diet the most permissive in this respect (Fig. 1). Semivegetarians, also called demivegetarians, partial vegetarians, or moderate vegetarians, include some but not all animal foods and usually exclude red meat. Lacto-ovovegetarians exclude meat, poultry, and fish, and lactovegetarians also exclude eggs. Strict vegetarians,

Vitamin C

Vegetarians daily consume between 500 and 1200 g of fresh fruits and vegetables12, 15, 16 and thus receive an abundance of vitamin C in their daily diet. In all reports on adult vegetarians (Table II) , the dietary intake of vitamin C has been well above the recommended level, between 198% and 973% of the recommeded daily allowance.17

There has been only one study on the status of vitamin C in vegans,11 and information on other vegetarians is also scanty (Table III). In all studies reviewed,11,

Vitamin E

Dietary intake of vitamin E (α-tocopherol) by vegetarians has been reported to be as high as 138% to 313% of the recommended daily allowance17 (Table II). Draper et al.12 reported that in vegans the major sources of vitamin E were grains and vegetable oils; Rauma et al.11, 15 reported that in “living-food” eaters the main sources were fatty seeds and nuts such as sesame and sunflower seeds and cashews.

The requirement for vitamin E increases when the intake of polyunsaturated fatty acids (PUFAs)

β-carotene

Vegetarians and especially vegans have high dietary intakes of β-carotene11, 12 (Table II). Vegan diets may also contain other hydrocarbon carotenoids such as α-carotene and lycopene and their oxygenated derivatives such as xantophylls,3 but intakes of these compounds have not been investigated.

Serum and plasma concentrations of β-carotene in vegetarians have been reported in five studies,11, 18, 20, 21, 37 that of total carotenoids in two studies,13, 38 and of α-carotene in one study.18 In all

Zinc and copper

Dietary intakes of zinc and copper by vegetarians differ considerably (Table VII) and depend on both selection of foods and the amounts of foods consumed. By excluding all foods of animal origin, vegetarians reduce their intake of zinc and increase their intake of copper.9 Bioavailability of zinc in vegetarian foods is markedly reduced by phytate and has been shown to be highly dependent on the molar ratio of phytate to zinc and that of calcium and phytate to zinc.9 The main dietary factors

Selenium

Large differences exist in estimated daily selenium intakes among vegetarians from different countries, ranging from as low as 7 μg among Swedish vegans51 to 113 μg by Canadian Seventh Day Adventists.52 The main sources of selenium for vegetarians are breads and cereals (46%); legumes, nuts, and soy products (24%); and vegetables (15%).52 Utilization of selenium from vegetarian diets needs to be studied.

Rauma et al.11 reported that the activity of erythrocyte glutathione peroxidase in Finnish

Summary and conclusion

Compared with omnivores, vegetarians have significantly higher levels of antioxidant vitamins (vitamin C, vitamin E, and β-carotene) in the plasma or serum, but comparable or in some cases lower levels of antioxidant minerals (zinc, copper, and selenium). The good antioxidant vitamin status in vegetarians is explained by high consumption of fruits, vegetables, and nuts.11, 12, 16 Although the consumption of fruits and vegetables correlates highly with dietary intakes of carotenoids and vitamin

References (57)

  • P.F Jacques et al.

    Comparison of micronutrient intake measured by a dietary questionnaire and biochemical indicators of micronutrient status

    Am J Clin Nutr

    (1993)
  • J Lehmann et al.

    Vitamin E and relationships among tocopherols in human plasma, platelets, lymphocytes, and red blood cells

    Am J Clin Nutr

    (1988)
  • E.J Johnson et al.

    Relation between β-carotene intake and plasma and adipose tissue concentrations of carotenoids and retinoids

    Am J Clin Nutr

    (1995)
  • E.D Brown et al.

    Plasma carotenoids in normal men after a single ingestion of vegetables or purified β-carotene

    Am J Clin Nutr

    (1989)
  • J.H Freeland-Graves et al.

    Zinc status of vegetarians

    J Am Diet Assoc

    (1980)
  • B.M Anderson et al.

    The iron and zinc status of long-term vegetarian women

    Am J Clin Nutr

    (1981)
  • O Hänninen et al.

    Effects of eating an uncooked vegetable diet for 1 week

    Appetite

    (1992)
  • N.R Reddy et al.

    Reduction in antinutritional and toxic components in plant foods by fermentation

    Food Res Int

    (1994)
  • M Abdulla et al.

    Nutrient intake and health status of vegans. Chemical analyses of diets using the duplicate portion sampling technique

    Am J Clin Nutr

    (1981)
  • R.S Gibson et al.

    The trace metal status of a group of post-menopausal vegetarians

    J Am Diet Assoc

    (1983)
  • B.M Calkins et al.

    Diet, nutrition intake, and metabolism in populations at high and low risk for colon cancer

    Am J Clin Nutr

    (1984)
  • K.C Janelle et al.

    Nutrient intakes and eating behavior scores of vegetarian and nonvegetarian women

    J Am Diet Assoc

    (1995)
  • M Abdulla et al.

    Nutrient intake and health status of lactovegetarianschemical analyses of diets using the duplicate portion sampling technique

    Am J Clin Nutr

    (1984)
  • B Halliwell et al.

    Free radicals in biology and medicine, 2nd ed

    (1989)
  • L Ernster

    Biokemisk och fysiologisk översikt av antioxidativa vitaminer

    Scand J Nutr

    (1994)
  • K.A Steinmetz et al.

    Vegetables, fruit, and cancer. II. Mechanisms

    Cancer Causes Control

    (1991)
  • M.J Jackson

    Symposium on “antioxidants.” Can dietary micronutrients influence tissue antioxidant capacity?

    Proc Nutr Soc

    (1994)
  • K.A Steinmetz et al.

    Vegetables, fruit, and cancer. I. Epidemiology

    Cancer Causes Control

    (1991)
  • Cited by (79)

    • The relationship of lipid peroxidation and antioxidant status to selected modifiable risk factors in coronary artery disease patients

      2021, International Journal of Cardiology: Hypertension
      Citation Excerpt :

      In the case of the nutritional group, a statistically significant decrease in SOD levels was obtained for patients having a non-vegetarian diet (Group E) when compared with patients having a vegetarian diet (Group D). This indicates a strong relation to lower antioxidant levels and nutritional habits and is concomitant with earlier reports [29,30]. This observation point out the need to increase the antioxidant status thereby lowering oxidative stress in CAD patients.

    • Quantification of mineral composition of Brazilian bee pollen by near infrared spectroscopy and PLS regression

      2019, Food Chemistry
      Citation Excerpt :

      The minerals calcium (Ca), magnesium (Mg), zinc (Zn), phosphorus (P) and potassium (K) were quantified through ICP OES by Morgano et al. (2012) for the same set of bee pollen samples. According to Morgano et al. (2012), the most abundant elements in the Brazilian pollen composition are Ca, Mg, P and K, whereas zinc, present in minor quantity, is considered an important antioxidant since it is a component of the superoxide dismutase (SOD) antioxidant enzyme (Rauma & Mykkanen, 2000). The authors found the following percentage contribution of the mineral elements to Brazilian recommended daily intake (RDI) for adults, considering a 25 g portion of pollen: Ca (5.5%), Mg (11.3%), Zn (16.7%), P (17.2%) and K (2.7%).

    • Analysis of health-related biomarkers between vegetarians and non-vegetarians: A multi-biomarker approach

      2018, Journal of Functional Foods
      Citation Excerpt :

      Although we did not notice differences in lipid peroxidation as measured by MDA, vegetarians could have lower antioxidant defence due to a lower level of antioxidant micronutrients (Zn, Cu, Se, Fe), GSH, GGT and uric acid. Based on the literature, the vegetarian type of diet helps to improve antioxidant status, lowers oxidative stress, and reduces blood lipid levels (Kim, Cho, & Park, 2012; Rauma & Mykkänen, 2000). However, based on the answers collected through our questionnaire it is clear that non-vegetarians also consume fruits and vegetables on a daily basis.

    • Nutritional Considerations for Dialysis Vegetarian Patients, Part One

      2018, Journal of Renal Nutrition
      Citation Excerpt :

      Kidney disease patients have been shown to have lower antioxidant levels and have increased oxidative stress compared with controls.4 In individuals following vegetarian diets, it has been shown that they maintain higher antioxidant levels, in particular vitamin C, vitamin E, and β-carotene.5 Other benefits of a vegetarian diet include helping control high blood pressure, decreased proteinuria, decreased levels of cardiovascular disease risk factors such as total cholesterol, low-density lipoprotein cholesterol and triglyceride levels, decreased inflammation, prevention of metabolic acidosis with a more alkaline diet, and improved insulin sensitivity.6-11

    • Vegetarian Diet and Possible Mechanisms for Impact on Mood

      2017, Vegetarian and Plant-Based Diets in Health and Disease Prevention
    View all citing articles on Scopus
    View full text