Friday, November 24, 2006

Part II of IV: Antioxidants - Sources and Dietary Intakes Antioxidants

Sources and Dietary Intakes Antioxidants can be vitamins, minerals, enzymes or plant derived nutrients called phytonutrients. The major vitamin antioxidants are vitamin C, vitamin E, beta-carotene, while selenium is the major mineral antioxidant. Many researchers and nutritionists discuss and report on "antioxidants" as if these were the only sources of importance. A thorough examination of antioxidants and their importance to human health must include a much larger list of compounds that are present in healthy, varied diet. The following list is an example of the wide variety of phytonutrient antioxidants present in a healthy diet:
Phytochemical : Food Source
Allyl Sulfides : Onions, garlic, leeks, chives
Carotenoids (e.g. lycopene, lutein, zeaxanthin) : Tomatoes, carrots, watermelon, kale, spinach
Curcumin : Turmeric
Flavonoids (e.g. anthocyanadins, resveratrol, quercitin, catechins) : Grapes, blueberries, strawberries, cherries, apples, grapefruit, cranberries, raspberries, blackberries
Glutathione : Green leafy vegetables
Indoles : Broccoli, cauliflower, cabbage, brussels sprouts, bok choy
Isoflavones : Legumes (peas, soybeans)
Isothiocyanates (e.g. sulforaphane) : Broccoli, cauliflower, cabbage, brussels sprouts, bok choy
Lignans : Seeds (flax seeds, sunflower seeds)
Monoterpenes : Citrus fruit peels, cherries, nuts
Phytic Acid : Whole grains, legumes
Phenols, polyphenols, phenolic compounds (e.g. ellagic acid, ferrulic acid, tannins) : Grapes, blueberries, strawberries, cherries, grapefruit, cranberries, raspberries, blackberries, tea
Saponins : Beans, legumes
Recommendations by the National Cancer Institute, the U.S.D.A., other government agencies and nutrition experts are to eat a minimum of 5-13 servings of fruits and vegetables per day, depending on calorie needs. Based on these recommendations, a typical varied diet would provide approximately 200-600 mg of vitamin C and 10-20 mg (16,000-32,000 IU) of carotenoids.
Overall, polyphenols are the most abundant antioxidants in the diet. Their total dietary intake could be as high as 1 gram/day in a mixed, varied diet of fruits, vegetables, grains, and beverages.
Possible intakes of other phytonutrient antioxidants would be:
  • anthocyandins " 2 oz black grapes 1,500 mg;
  • proanthocyanidins " 100-300 mg/d red wine;
  • catechins " 50 mg day " tea (one cup brewed green tea " 240-320 mg catechins), chocolate, apples, pears, grapes, red wine;
  • isoflavones " 50 mg/day from soy foods;
  • chlorogenic acid " as high as 800 mg/day coffee drinkers.
Although it may seem reasonable that a consistently healthy and varied diet could provide high doses of antioxidants, the average American gets a total of just three servings of fruits and vegetables a day. The latest dietary guidelines call for five to thirteen servings of fruits and vegetables a day, depending on one's caloric intake. For a person who needs 2,000 calories a day to maintain weight and health, this translates into nine servings, or 4½ cups per day.
The 2001-2002 NHANES survey of dietary intakes shows that 93% of Americans fail to get even the Estimated Average Requirement (EAR) for vitamin E, let alone the RDA. More than half of adults fail to get even the average requirement for vitamin A. About one-third of non-smokers and two-thirds of smokers fall short on minimum vitamin C requirements.
If the governmental dietary recommendations are meant to be taken seriously, then it follows that it would be better for people to achieve recommended amounts of nutrients than to fall short. Obviously, since the average intake of 3 servings or less of fruits and vegetables fails to provide minimum levels of even basic vitamins, intakes of the numerous other antioxidants are sure to be well under optimal and beneficial levels.
It has been established that a good multivitamin can fill in gaps in missing vitamins, but availability of broad spectrum antioxidant supplements has lagged behind. Although there is much to be learned about the characteristics of the literally hundreds of dietary antioxidants, it seems reasonable that providing supplements of various antioxidant classes may fill in nutritional gaps and provide many of the benefits missing from the typical American diet.
Source: USANA Health Sciences