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Oxygen radicals are not all bad; some oxygen radicals are essential to help cells generate energy and fight infections. However, when reactive oxygen species are overabundant, they cause oxidative stress. The body has a series of enzymatic mechanisms to prevent oxidative stress, and the presence of antioxidants is integral in this regard. Antioxidants prevent or reduce oxidative stress by neutralizing oxygen radicals. This involves either providing the extra electron oxygen radicals need, thereby stabilizing them, or dissolving the molecules entirely. On its own, the human body does not produce enough antioxidants to combat the oxidative stress caused by a daily onslaught of internal and external factors, which is why consuming a diet rich in sources of antioxidants, such as plant foods, is so important.
Whether caused by the metabolic process, environmental factors, or dietary deficiencies, oxidative stress inevitably triggers the body’s further production of oxygen radicals, which research indicates causes damage to DNA (Wu and Cederbaum, 2003; Franco et al., 2008; Donkena et al., 2010). The injuries to DNA can range from the breaking of DNA strands to chromosomal rearrangements to, most notably, the abnormal expression and suppression of genes and atypical cell growth. In particular, chronic oxidative stress has an adverse effect on a mechanism responsible for turning on or turning off genes: DNA methylation. Although a full-scale discussion of DNA methylation is beyond the scope of this article, it is important to note that in recent years DNA methylation—which plays an important role in gene transcription—has emerged as an important biomarker for cancer. Hypermethylation contributes to the silencing of tumor-suppressing genes, and hypomethylation is linked to the unchecked expression of tumor growth (Das and Singal, 2004; Franco et al., 2008; Donkena et al., 2010).
Emerging research suggests that certain bioactive compounds in foods may deter the development of cancer by affecting DNA methylation. Compounds such as epigallocatechin 3-gallate (EGCG) in green tea, genistein from soybeans, and isothiocyanates in green vegetables reduce DNA hypermethylation, thereby increasing the expression of tumor-suppressing genes (Fang et al., 2007; Choi and Friso, 2010). Because aberrant DNA methylation is also associated with obesity (Wang et al., 2010) and may thus be a contributing factor to type 2 diabetes and other obesity-related disorders, the food compounds shown to be effective in controlling DNA methylation in cancer may also have a positive effect on the mitigation of obesity-related diseases.
The Gene That Doesn’t Like Green(s)
Scientists have identified several genes and gene variants that are associated with an increased risk of developing cardiovascular diseases. Some of these genes predispose people to high cholesterol levels, some are linked to an increased risk of plaque buildup in arteries, and still others are associated with elevated blood pressure. While scientists continue to research which genes are directly responsible for different diseases and which play supporting roles, chromosome 9p21 has emerged as one of the most significant genes in predicting heart disease. A study by researchers at McGill University and McMaster University revealed that people who possess the 9p21 gene and consumed at least two servings of vegetables (especially raw and green leafy veggies) and fruits per day lowered their risk of developing heart disease. In addition, carriers of the 9p21 gene who ate the least amount of vegetables had a two-fold increase in risk for a heart attack (Do et al., 2011). This important revelation may be the reason that studies had previously suggested that diets rich in vegetables and fruits lowered the risk of cardiovascular diseases. The McGill-McMaster study also indicated that people with the highest daily intake of vegetables and fruits were 30% less likely to experience a heart attack or stroke.