Several years ago the National Cancer Institute introduced its “5 A Day for Better Health” program to encourage all of us to eat five or more servings of fruits and vegetables every day. Many other scientific bodies similarly have encouraged this practice as a way for us to protect against not just cancer, but also cardiovascular disease, declining mental functioning, reduced memory and other forms of deterioration associated with aging. Initially, it was thought that these benefits come mostly from antioxidant mechanisms and thus vitamins C and E were primarily responsible. However, more recent studies have shown that important aspects of the protection afforded by fruits and vegetables derive from the quantity and the variety of polyphenols, carotenoids and other phytonutrients found in them. These nutrients may be providing benefits that are unrelated to classic antioxidant mechanisms.
Bad News for Antioxidants?
A dozen years ago, the consensus was it is the antioxidant capacity of plant foods that is important. Today, researchers are much less convinced that “phytonutrients,” “polyphenols,” and other names for plant nutrients should be equated with “antioxidants.” Mind you, the benefit of eating more fruits and vegetables is not in doubt. However, a declining percentage of researchers believe it is the antioxidant qualities of plant nutrients that are protective. There are many reasons for this change of heart.
- Since the late 1990s, large trials with individual antioxidants and their precursors.vitamin C, vitamin E, beta-carotene, selenium, and so forth.at best have yielded disappointing results. Some trials have yielded negative results. If such classic individual antioxidants have failed to consistently yield results, the proven benefits of polyphenols likely are related to other mechanisms.
- Many phytonutrients, although shown to be significant antioxidants in in vitro tests, are absorbed in only tiny amounts from the intestinal tract. Proanthocyanidins and other polyphenols from grape seed, red wine and cocoa are good examples of this phenomenon.
- Polyphenol benefits may be linked to signaling functions. This mechanism would parallel one of the actions of ubiquiniol/ ubiquinone (QH/CoQ10), which benefits blood pressure apparently through a signaling mechanism rather than by acting as an antioxidant.
- Polyphenols may produce a number of benefits without ever being absorbed into the blood stream or lymphatic system. For instance, indirect effects have been identified for the flavonols of cocoa working as prebiotics. Over a period of four weeks in human volunteers, 494 mg/day of a high flavonol extract increased Bifidobacterium and Lactobacillus and decreases in clostridia, a pro-inflammatory bacteria. The magnitude of the benefits were similar to those found with 5 to 10 grams/day of soluble fiber prebiotics, such as fructooligosaccharides.
Matters are not entirely bleak for the antioxidant thesis, but it does need to be reevaluated and retooled. Food sources of polyphenols and other “antioxidants” are back in the news because their combinations of nutrients appear to be far more protective than is supplementation with individual antioxidant vitamins.
ORAC Is Still Useful!
Remember that polyphenols generally are powerful antioxidants in vitro. This means that regardless of whether phytonutrients are beneficial by acting directly as antioxidants, one means of measuring the phytonutrient payload of fruits and vegetables is to test for antioxidant capacity. To help quantify the protective value of foods, the Jean Mayer USDA Human Nutrition Research Center at Tufts University for years has utilized a special test called ORAC (the Oxygen Radical Absorbance Capacity test) to evaluate the capacities of different foods to prevent oxidative damage. The ORAC test yields results in a form sometimes referred to as ORAC “units.” These units are calibrated on a scale based upon the antioxidant effects of a special form of vitamin E. The more ORAC units found with a test sample, the better that sample performed as an antioxidant under defined laboratory conditions.
Scientists have gone further than just testing various foods outside of the body, however, and this is where matters become interesting. The ORAC test has been performed with blood drawn from human subjects to validate that the expected protection actually appears. Moreover, animal studies have shown that polyphenol-rich foods can prevent declines in memory and learning ability and maintain the capacity of the brain to respond to chemical signals, as well as affording protection against damage to the blood vessels. Therefore, it has been shown that polyphenols and other plant nutrients can protect against various types of damage to the body and that there is a correlation between this protection and ORAC findings even though these phytonutrients may be getting into the system only in small amounts.
Here is an example of what happens when polyphenols are consumed along with vitamin antioxidants: An extract from grape seeds was given to human volunteers and led to a much greater increase in the antioxidant capacity of the subjects’ blood than is theoretically possible based upon the antioxidant capacity of grape seed alone. The same grape seed extract demonstrated significant synergism when tested with the antioxidant vitamins C and E, either alone or in combination. This type of trial is especially interesting because very little grape seed extract crosses into the blood. Remember, antioxidant vitamins are present in the human body at levels typically twenty to several hundred times those of plant polyphenols, the active antioxidant compounds found in tea, wine and grape juice.
In the tests performed at the University of Scranton by Joe Vinson, grape seed extract taken with either vitamin C or vitamin E improved the antioxidant capacity of volunteers’ blood as much as 125 percent more than the total antioxidant capacity of all the starting materials combined! In other words, the phytonutrient was acting as more than just an antioxidant and one result of this was a synergistic improvement in the total antioxidant capacity of the blood.
Are Five Servings of Fruits and Vegetables Per Day Enough?
Based upon tests with 36 men and women ranging from 20 to 80 years of age, researchers at Tufts found that the average ORAC value of the five fruit and vegetable servings these subjects normally ate per day was 1,670 ORAC units. In an experiment, these subjects increased their intake to 10 servings of fruits and vegetables per day to supply the equivalent of between 3,300 and 3,500 ORAC units. The result was that blood samples drawn from these volunteers had plasma antioxidant values which were 13 to 15 percent higher than were those drawn from the same subjects after they had eaten their normal diets. An elevation in plasma ORAC capacity of 15 percent is considered to be significant because the antioxidant capacity of the blood is tightly controlled and difficult to increase to any large extent.
Not all foods are created equal when it comes to ORAC values. For instance, when tested with eight women volunteers, ten ounces of spinach increased plasma antioxidant values better than did 1,250 milligrams of vitamin C. An eightounce serving of strawberries was slightly less effective than the vitamin C, but a little more effective than 9.6 ounces of red wine. Another plus for all three of these foods, of course, is they provide substances which are useful for purposes other than just antioxidant protection. Recent work with red wine, for instance, indicates that some of its components help to reduce elevated blood pressure. Similarly, spinach, although rated less good than strawberries on the ORAC scale, in actual animal trials was better than either strawberries or vitamin E in maintaining long-term memory as the animals aged. Here, again, there is protection from the phytonutrients that cannot be explained in terms of antioxidant mechanisms.
An interesting finding from the ORAC tests is that some foods have stunningly high ORAC values and can be consumed daily in relatively small amounts to achieve the protection which the 36 volunteers gained by increasing their consumption of fruits and vegetables. Researchers at Tufts, including Guohua Cao and Ronald Prior, suggest that a daily intake of 3,000 to 5,000 ORAC units is a good level to maintain to improve the antioxidant capacity of the blood and tissues. To achieve this type of intake, an individual needs to add only the equivalent of one cup of blueberries—supplying 3,200 ORAC units—to his or her daily diet.
Putting Together A Program
To achieve the desired ORAC unit intake is not hard to do, but, unfortunately, many of the foods which we normally consume in the belief they are offering protection are quite poor in antioxidant capacity. On the one hand, iceberg lettuce, to take one of the most commonly consumed foods, is very low on the ORAC scale: 3.5 ounces of iceberg lettuce supplies less than 150 ORAC units, and some other typical salad vegetables, such as celery and cucumber, are even less good as sources of antioxidants. On the other hand, vegetables such as kale, spinach, broccoli and Brussels sprouts achieve high marks on the ORAC scale. A 3.5 ounce serving of any of these latter vegetables (not overcooked!) will supply between 600 and 1,000 ORAC units, which means that “5 A Day” will satisfy the Tufts’ University researchers’ recommendation.
Getting your Daily Polyphenol and Antioxidant Protection
An important aspect of the protection afforded by fruits and vegetables comes from the quantity and the variety of polyphenols and antioxidants found in them. To help quantify the protective value and evaluate the capacities of different foods to prevent oxidative damage, the Jean Mayer USDA Human Nutrition Research Center at Tufts University uses a test called ORAC (the Oxygen Radical Absorbance Capacity test). The data found here is based on the original test findings circa 2000 for consistency. For the latest findings, see USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 (May 2010).
It is easy to consume the Recommended Daily Intake of ORAC protective units. In the chart below, fruits and vegetables with established ORAC values are grouped into four categories. The ORAC units per 100 grams are listed after each food item. Choose at least two fruit and three vegetable sources daily to supply the recommended 3,000 to 5,000 ORAC units. Whatever your choices, make sure they add up to “5 A Day.”
Category A Category B Category C Category D High ORAC Fruits (Whole Fruit, Not Juice)* High ORAC Vegetables** Low to Moderate
ORAC Fruits (Whole Fruit, Not Juice)
Low to Moderate ORAC Vegetables 1 choice = 1 fruit unit 2 choices will satisfy your fruit daily needs. 1 choice = 1 vegetable unit 3 choices will satisfy your daily vegetable needs 2 choices = 1 fruit unit 4 choices will satisfy your daily fruit needs 2 choices = 1 vegetable unit 6 choices will satisfy your daily vegetable needs ORAC units per 100-grams/3.5 oz. 1. ORAC units per 100 grams/3.5 oz. ORAC units per 100 grams/3.5 oz. 2. ORAC units per 100 grams/3.5 oz. Blueberries
Red Bell Pepper
- Fruits and vegetables not listed can be assumed to fall into the “low to moderate” categories.
- *Does not include high-calorie dried fruits, e.g., prunes (5,770) or raisins (2,830)
- **Does not include condiments, herbs or spices, e.g., garlic, cilantro, turmeric, etc.