“Antioxidant” has become synonymous with “disease prevention” and “anti-aging” in many people’s eyes. Yet despite the many claims about various foods’ and supplements’ antioxidant content and benefits, there is no single official measure of antioxidant content of food or of antioxidant status of the body. Recommendations to eat more fruits and vegetables to get antioxidants – or a perceived need for antioxidant supplements because that goal is too challenging – need to evolve in light of new research about polyphenols and other phytochemicals in plant foods. Studies that focused on effects of these compounds in laboratory tests do not reflect what they do in our bodies.
This is the first segment of a video interview with Britt Burton-Freeman, PhD, MS, a researcher studying how these phytochemicals, on which we previously focused as antioxidants, can work to promote health and fight chronic diseases like heart disease, type 2 diabetes and cancer. Dr. Burton-Freeman is Director of the Center for Nutrition Research at the Institute for Food Safety and Health, Illinois Institute of Technology; and Associate Researcher in the Department of Nutrition at the University of California, Davis.
After viewing the video with Dr. Burton-Freeman, please read on about some of the common misunderstandings about antioxidants in light of current research: what terms like oxidative stress and antioxidants mean; why they can each be both good and bad; why claims about foods, diets or supplements resting on ORAC or other tests of antioxidant power no longer hold up; and what our new understanding of phytochemicals in plant foods means for health.
In our video interview, you heard Dr. Burton-Freeman refer to antioxidants as “free radical scavengers”. You’ve probably heard that phrase before, but what does it mean? Some of you, like me, probably find the science of this exciting; the resource list provides further reading for you. Even if you just care about the bottom line, however, to make sense of news stories and product claims with which you are bombarded today, you need to be able to go beyond that simple phrase.
Common Misunderstandings about Free Radicals
- Free radicals form naturally in the body as nutrients from food are oxidized during normal metabolism to produce fuel for our activity and for our body organs to function. In addition, sunlight and some other forms of radiation, and some environmental toxins (such as tobacco smoke and certain metals), may contain high levels of free radicals or stimulate the body’s cells to produce more free radicals.
- Free radicals can build up and damage cells, increasing risk of a variety of chronic diseases we often associate with aging. Damage that changes cells’ DNA may lead to cancer. Damage to cell membranes and proteins can inhibit cell function and promote development of heart disease and diabetes. As free radicals try to become stable by stealing electrons from other molecules, these molecules may in turn become unstable free radicals, beginning a cascade of free radical production and promoting a chronic low-grade inflammation throughout the body.
- Free radicals are not all bad, however. At low levels, free radicals are an important part of body signaling systems to maintain normal immune function, stimulate self-destruction (apoptosis) of abnormal cells before they develop into cancer, and trigger the body’s own innate antioxidant defense system.
Evolving Understanding of Antioxidants
- Antioxidants protect cells by interacting with and neutralizing free radicals. When you think of antioxidants as “free radical scavengers”, you might think of an antioxidant as a sponge that soaks up a spill before it has the chance to spread and stain or damage your counter or furniture. Or more accurately, you might think of an antioxidant as a buffer that can mix with an acid and neutralize it.
- Some antioxidants (called endogenous antioxidants) are produced within the body. This natural “antioxidant defense system” includes a variety of enzymes as well as compounds such as glutathione, melatonin and uric acid.
- Our own antioxidant production can’t handle all the free radicals that confront the body, however. We need other antioxidants, such as vitamins A, C and E, from our food. Laboratory research shows that antioxidants like these can help prevent the signs of free radical damage considered markers of health risk.
- Despite this crucial role of antioxidants in protecting health, research now indicates that excessive amounts may not be healthful. Since low levels of free radicals play an important role in normal body processes, neutralizing too many removes this natural protective function. In addition, studies show that the same compounds that are antioxidants at moderate levels can become pro-oxidant and pro-inflammatory at high levels.
- Antioxidants are not interchangeable with each other. Each has unique properties, enabling it to play a specific role and work in a particular part of cells. So loading up on one antioxidant can’t completely “cover” for lack of others. It’s like a symphony that needs to play together.
Polyphenols & Other Phytochemicals Not What We Thought
An exciting area of research has been the growing recognition that we get much more than fiber and nutrients like vitamins and minerals when our eating patterns are centered around plant foods like vegetables, fruits, whole grains, beans, nuts and seeds. Thousands of natural compounds – “phytochemicals” – in these foods, as well as drinks like coffee and tea, have been discovered and seem to play a crucial role in these foods’ health protective effects.
- A variety of laboratory tests were developed to test how good a job compounds could do as antioxidants. You’ve probably seen books, articles and product claims recommending compounds like flavonoids and other polyphenols; and foods that supply them, such as berries, grapes, apples, onions, and tea; for their high antioxidant power based on ORAC and other test scores. In laboratory studies, many of these compounds show antioxidant effects expected to be health-protective.
- Yet further research has shown that for many phytochemicals, only a very small proportion we eat get absorbed out of the digestive tract. Research still supports potential for health benefits, and these phytochemicals can be broken down to other compounds that can be absorbed. The essential point, however, is that tests of these foods, or the compounds as they are supplied in foods, cannot represent what happens in the body when we consume them.
The Evolving Understanding: Foods Supplying Phytochemicals Matter
A new understanding of oxidative stress and compounds we valued as antioxidants is taking shape. Although previous laboratory studies that focused on antioxidant effects of phytochemicals themselves don’t apply, animal and human studies suggest that foods and drinks rich in polyphenols and other protective phytochemicals may act through a variety of mechanisms that extend beyond antioxidant function.
- Short-term human intervention trials, as well as cell and animal studies, suggest that the compounds formed within the body from phytochemicals in healthful plant foods may play important roles in cell signaling pathways and gene expression that affect inflammation, insulin resistance, cancer development, atherosclerosis and blood pressure.
- Studying consumption of these compounds over long periods of time in large populations poses many challenges. Evidence is limited so far, but researchers see potential. Some studies do show people with diets higher in total flavonoids (one category of polyphenol phytochemical) had lower levels of a marker of inflammation and fewer deaths from heart disease.
Why the Science Matters
If antioxidant power measured in a test tube was the source of health protection, then loading up on anything with high antioxidant scores would be a key strategy for promoting health. What researchers have learned now:
♦ More is not always better – antioxidants and free radicals both are double-sided, with too little and too much posing risk. The goal is a health-promoting balance.
This has practical implications for questions about antioxidant supplements during cancer treatment (some of which work by creating free radicals to destroy cancer cells) and for prevention of cancer, heart disease and more. The amount of antioxidant power that best achieves that balance is sure to vary among individuals depending on differences in the free radical load to which they are exposed and personal genetic and health factors.
Research in humans has not demonstrated that taking antioxidant supplements can help reduce the risk of developing or dying from cancer, and some studies have even shown an increased risk of some cancers. The American Heart Association specifically states that antioxidant supplements are not recommended. Getting enough vitamin E in our diet seems to promote health, but high-dose supplements (400 IU/day or greater) may actually increase risk of prostate cancer and deaths from all causes.
♦ Relying on test tube measures of antioxidants as an answer for healthy food choices is missing the boat. Yes, high scores likely mean foods are high in polyphenols, which do seem to offer a variety of health-protective effects. However, these compounds act in forms other than what we consume in food. What is actually delivered to our body cells varies with how a food is prepared, what other foods are consumed with it, and how the phytochemicals are metabolized (which varies among individuals based on genetics and the bacteria in our colon that do much of the work).
Bottom line: Compounds formerly of interest as antioxidants are of more interest than ever for potential roles in promoting health and reducing risk of chronic disease. BUT aiming for ever-higher levels of antioxidant-specific function is not the key to these benefits. What’s next? Come back for more, when Dr. Burton-Freeman explains what research does support about impact on health and what sort of practical steps we can take that are enough to make a difference.
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(For those who want some more on the science: Free radicals are molecules that are chemically unstable, which creates a strong pull for them to react with other substances. A free radical forms when an atom or a molecule either gains or loses an electron. Seeking stability, free radicals try to steal electrons from other molecules. The most common free radicals formed in living tissues contain the element oxygen; scientists often refer to them as “reactive oxygen species,” or “ROS”. Other free radicals are based on nitrogen. Antioxidants work by donating electrons to neutralize free radicals without becoming free radicals themselves.)
For more details on antioxidants, check the National Cancer Institute (NCI) factsheet, Antioxidants and Cancer Prevention and Antioxidants: Beyond the Hype, from The Nutrition Source at Harvard University.
Here is the USDA statement explaining why it took down the ORAC database.
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