Sunday, April 29, 2012

The Nutrition Debate #50: Free Radicals and Oxidative Stress

In The Nutrition Debate #46, we posited that oxidative stress was one of the three prime contributors to cardiovascular disease, along with inflammation and imbalances in blood sugar and insulin. But, what is oxidative stress and what causes it? Oxidative stress is an imbalance between the production of reactive oxygen species (ROS) and the body’s ability to neutralize them. Thus, a delicate balance is required. Too many reactive oxidizing species or too few (or ineffective) anti-oxidant defenses produce oxidative stress. And oxidative stress can lead to atherogenesis, etc., etc.
Free Radicals are one of the most common ROS. They have an unpaired electron that makes them highly reactive chemically, but also generally short-lived. The long-lived free radicals can be dangerous, depending on their stability. According to Wikipedia, “Excessive amounts of these free radicals can lead to cell injury and death, which may contribute to many diseases such as cancer, stroke, myocardial infarction and diabetes. Many forms of cancer are thought to be the result of reactions between free radicals and DNA, potentially resulting in mutations that can adversely affect the cell cycle and potentially lead to malignancy.”
Some of the symptoms of aging such as atherosclerosis are also attributed to free-radical induced oxidation of many of the chemicals in the body. In addition, free radicals contribute to alcohol-induced liver damage, perhaps more than alcohol itself. Radicals in cigarette smoke are implicated in the process that promotes the development of emphysema.
But, free radicals play an important role in a number of biological processes, and “some of these are necessary for life such as the intracellular killing of bacteria by… macrophages,” according to Wikipedia. See column #48. So, because some free radicals are necessary for life, the body produces a number of enzymes to minimize free radical-induced damage and to repair damage that does occur. In addition, antioxidants play a key role in these defense mechanisms. Research is underway to determine the relative importance and interactions between antioxidants. In the meantime the use of antioxidant supplements to prevent disease is very controversial; real food sources are probably the best choices and very tasty too.
Antioxidants are classified into two broad divisions, depending on whether they are water soluble or fat soluble. These compounds may be synthesized in the body or obtained from the diet or through supplementation. Some are mostly present within cells, while others, such as uric acid, are more evenly distributed. In fact, human blood has a high concentration of water-soluble uric acid. Antioxidants are found in vegetables, fruits, grains, eggs, meat, legumes, and nuts. Herbs and spices are particularly high in antioxidants.
·         Vitamin C (ascorbic acid): Bell pepper, parsley, broccoli, Brussels sprouts, cauliflower, kale (see list here).
·         Vitamin E (tocopherols, tocotrienols): green leafy vegetables, almonds, asparagus, papaya (see list here).
  • Polyphenolic antioxidants (flavonoids): tea, coffee, fruit, olive oil, chocolate, red wine, and herbs and spices  (top 10 list here).  Also, see this 2002 Science Daily reprint from the American Chemical Society.
·         Carotenoids (lycopene, carotenes, lutein): sweet potatoes, spinach, tomatoes,  and chili peppers (see list here).
In general, processed foods contain fewer antioxidants than fresh and uncooked foods, since generally the preparation process exposes the food to oxygen.
Again, Wikipedia: “The paradox in metabolism is that, while the vast majority of complex life on Earth requires oxygen for its existence, oxygen is a highly reactive molecule that damages living organisms by producing reactive oxygen species. Consequently, organisms contain a complex network of antioxidant metabolites and enzymes that work together to prevent oxidative damage to cellular components such as DNA, proteins and lipids. In general, oxidant systems either prevent these reactive species from being formed, or remove them before they can damage vital components of the cell. However, reactive oxygen species also have useful cellular functions, such as redox signaling. Thus the function of antioxidant systems is not to remove oxidants entirely, but instead to keep them at an optimum level.” The oxidative challenge in biology is to maintain proper cellular homeostasis -- a balance between reactive oxygen production and consumption. Diet and lifestyle play a large role in this complex system… and you are in charge.
 © Dan Brown 4/29/12

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