Can dietary micronutrients influence tissue antioxidant capacity?

Could a vegetarian diet reduce exercise-induced oxidative stress? A review of the literature

Oxidative stress is a natural physiological process that describes an imbalance between free radical production and the ability of the antioxidant defence system of the body to neutralize free radicals. Free radicals can be beneficial as they may promote wound healing and contribute to a healthy immune response. However, free radicals can have a detrimental impact when they interfere with the regulation of apoptosis and thus play a role in the promotion of some cancers and conditions such as cardiovascular disease. Antioxidants are molecules that reduce the damage associated with oxidative stress by counteracting free radicals. Regular exercise is a vital component of a healthy lifestyle, although it can increase oxidative stress. As a typical vegetarian diet comprises a wide range of antioxidant-rich foods, it is plausible that the consumption of these foods will result in an enhanced antioxidant system capable of reducing exercise-induced oxidative stress. In addition, a relationship between a vegetarian diet and lower risks of cardiovascular disease and some cancers has been established. This review explores the current available evidence linking exercise, vegetarians, antioxidants, and oxidative stress.

Antioxidant status in vegetarians versus omnivores

Every day, vegetarians consume many carbohydrate-rich plant foods such as fruits and vegetables, cereals, pulses, and nuts. As a consequence, their diet contains more antioxidant vitamins (vitamin C, vitamin E, and beta-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, beta-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.

An overview of methods for assessment of free radical activity in biology

Assays which purport to assess free radical activity in biological systems are multiple. However, despite numerous published descriptions of new methods and modifications of methods to assess free radical activity in biological materials, there is still a lack of reliable techniques for quantification of activity in vivo. Analysis of a number of related indicators and use of a variety of approaches appears the only reliable way to evaluate these processes in vivo. In studies of free radical generation by contracting skeletal muscle we have attempted to use a variety of indicators, including measurement of endogenous antioxidant levels, measurement of indirect indicators of free radical activity (e.g. products of lipid peroxidation, DNA oxidation or protein oxidation) and, where possible, measurement of direct indicators of free radical activity by electron spin resonance techniques. In view of the relative lack of specificity of many available techniques, caution should be exerted in evaluating the numerous examples of isolated single measures of free radical activity which are present in the scientific literature.

A diet rich in fat and poor in dietary fiber increases the in vitro formation of reactive oxygen species in human feces

Production of reactive oxygen species in the lumen of the colon, a process that is influenced by nutritional factors, may be important in the etiology of colorectal cancer. Because research on humans in support of this hypothesis is lacking, the objective of this study was to measure the effect of different dietary compositions on the in vitro oxygen radical production in human feces. Over a period of 12 d, seven healthy subjects received a diet rich in fat (50%) and meat and poor in dietary fiber. After a period of 1 wk, they received a vegetarian diet poor in fat (20%) and rich in dietary fiber. At the end of each study period, feces were collected and analyzed for in vitro oxygen radical production with dimethylsulfoxide as the free radical scavenger. The mean hydroxyl radical production was 13 times greater in feces of subjects when they consumed the diet rich in fat and poor in dietary fiber [52.7 +/- 29.5 micromol/(g feces x h)] than when they consumed the diet poor in fat and rich in dietary fiber [3.9 +/- 3.9 micromol/(g feces x h); P < 0.05]. This difference was associated with a 42% higher fecal iron concentration when they consumed the first diet (7.0 +/- 19.2 micromol/g feces) than when they consumed the second (4.9 +/- 1.9 micromol/g feces; P < 0.05). The results of this study confirm that diets high in fat and meat and low in fiber markedly increase the potential for hydroxyl radical formation in the feces, which in turn may contribute to an enhanced risk of colorectal cancer.