The Promise of Antioxidants: What You Need to Know by Christina Badaracco, MPH, RD
Americans have recently stepped up their research into how to optimize their health—perhaps prompted, in part, by the ongoing COVID-19 pandemic. From our expanded interest in dietary supplements to paying more attention to what is in our food, we are re-examining the role that antioxidants play in preventing chronic and infectious diseases. While antioxidants can be found in many different foods and supplements, the potential health benefits of some of them have yet to be proven.
What are the physiological roles of antioxidants?
Our bodies form molecules called “free radicals” as a natural byproduct of metabolism and exposure to external factors such as environmental pollution, excessive sun exposure, cigarette smoke and unhealthy foods. These molecules are chemically unstable and can lead to uncontrolled cascades of reactions, resulting in damage in our DNA, lipoproteins (or molecules that transport lipids) and other molecules. A high presence of free radicals creates a state of “oxidative stress.” Eventually, this damage and stress can lead to heart disease, cancer, Parkinson’s disease and many other chronic medical conditions. The role of antioxidants is to help stave off this oxidative stress by giving up electrons to free radicals—which stops the process. See our previous post about oxidative stress for more information.
Where are antioxidants found in our food?
There are likely thousands of different types of antioxidants, each with very different chemical structures, functions and sources. These compounds may include certain vitamins, minerals or other chemicals found in plants (or phytochemicals). Some of the most familiar include vitamin C, beta-carotene and resveratrol. When we eat antioxidant-rich fruits and vegetables, we benefit from the antioxidant molecules that protected the living plants. Indeed, plant-based foods—ranging from green leafy vegetables to seeds to red fruits—are typically the richest dietary sources of antioxidants. A few, such as selenium and coenzyme Q10, are found in animal foods (like shellfish and organ meats). Refer to the table below for some of the antioxidants mentioned in this paragraph. Click here for a more complete list of antioxidants with their food sources and associated benefits.
Spices and herbs can also be a great dietary source of antioxidants because they provide concentrated sources of the antioxidants found in fresh plant material. The five most concentrated sources are cloves, oregano, ginger, cinnamon and turmeric; interestingly, these all come from different parts of their respective plants. For example, cinnamon comes from tree bark, while ginger comes from a plant’s root. Thankfully for home cooks, scientists have found that spices retain most of their antioxidant properties when dried, making them nearly as nutritious as fresh varieties. Spices have been used for medicinal and functional purposes for many thousands of years; long before societies knew about their chemical composition, their antioxidant activity provided potent healing properties that made them valuable worldwide.
Cooking methods that apply heat can destroy antioxidant content in foods, however. In general, cooking for less time with a dry heat method will help to retain the most antioxidants. Refer to our Instagram post on this topic to read more about the best cooking methods to retain nutrients (including antioxidants).
What is the evidence for the impact of antioxidants from food and supplements on our health?
Antioxidants have received public attention since the 1990s, and a significant amount of research continues to investigate their potential roles in promoting health and treating disease. While diets rich in foods containing antioxidants are commonly associated with reduced disease risk, there is little evidence to show that individual antioxidants can play a significant role in preventing chronic disease.
In 2010, researchers from the USDA Nutrient Data Laboratory created a food database based on the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods scoring system. This assay, developed first in 1993, measures the extent to which the antioxidants inhibit oxidation in certain foods; a higher score indicates more benefit. Dried parsley has a score of 76730, for example, while a typical beer may have a score of 150. But while this system theoretically provides a handy method for ranking foods and making recommendations about foods to prioritize to patients and the public, scientists have since questioned its accuracy and usefulness. Their concerns are that the scores foods are given don’t necessarily translate to antioxidant activity in the body, nor does it account for other important nutritional factors such as fiber content. While many food companies capitalized on this rating system to market their products, such claims are not based on the latest evidence and can thus be misleading.
Overall, researchers are still uncertain whether consuming large amounts of antioxidants in supplement form benefits health. There is also some concern that consuming antioxidant supplements in excessive doses may be harmful. The Food and Drug Administration doesn’t regulate dietary supplements for safety, purity, and effectiveness, so buyers must be aware of the potential variability in their quality. Overall, leading health organizations such as the National Cancer Institute and the American Institute for Cancer Research recommend consuming abundant antioxidants through food rather than isolated supplements to prevent potential negative effects and until further research can prove efficacy and safety.
Further, antioxidants generally function best in combination with other chemicals—including other antioxidants—further indicating that whole foods are likely the optimal source. Food may also contain more diverse types of antioxidants than supplements; for example, alpha-tocopherol is the form of vitamin E commonly found in supplements, while in food, eight forms of vitamin E naturally exist. Each form can play a different role in the body, suggesting that we can benefit most from consuming a variety of forms.
How can I incorporate more antioxidants into my diet?
Aim to consume as much as you can through a plant-rich diet and talk with your dietitian or doctor about taking supplements if you have known deficiencies or cannot eat sufficient amounts through food.
Try to eat foods as close to their whole form as possible to maximize the number of antioxidants you will consume. While you don’t need to eat all raw foods, eat foods prepared in a variety of ways (including some in raw form) to optimize intake of all important nutrients.
Eat foods with as many possible colors (including white: onions, garlic) to ensure you’re consuming all of the antioxidants your body needs to protect itself.
Use a variety of spices and herbs in your cooking every day to add additional sources of antioxidants. Enjoy the exciting flavors they add to your food, as well.
When possible, choose wild foods—such as wild blueberries, dandelions and sockeye salmon—to maximize the potential antioxidant content of your meals.
For more tips about choosing foods high in antioxidants, visit Eatwild.com.
Cao G et al. Oxygen-radical absorbance capacity assay for antioxidants. Free Radical Biol. Med. 1993; 14:303-311. pubmed.ncbi.nlm.nih.gov/8458588/
Harvard TH Chan School of Public Health. “Antioxidants.” hsph.harvard.edu/nutritionsource/antioxidants/.
Linus Pauling Institute. “Lignans.” Oregon State University. Updated in 2010. . https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/lignans.
Medline Plus. “Antioxidants.” US National Library of Medicine. medlineplus.gov/antioxidants.html.
National Center for Complementary and Integrative Health. “Antioxidants: In Depth.” nccih.nih.gov/health/antioxidants-in-depth.
Tempest, M. Adding Spice for a Healthier Life—Evidence Shows Antioxidant-Rich Herbs and Spices May Cut Chronic Disease Risk. Today’s Dietitian. 2012; 14(3): 40. todaysdietitian.com/newarchives/030612p40.shtml.
Tempest, M. Antioxidants—Research Continues to Reveal Their Health-Promoting Effects. Today’s Dietitian. 2011; 13(5): 32. todaysdietitian.com/newarchives/050311p32.shtml
US Forest Service. “Tannins.” https://www.fs.fed.us/wildflowers/ethnobotany/tannins.shtml.
Christina Badaracco, MPH, RD
Christina is a registered dietitian and author who aims to improve access to healthy and sustainable food and educate Americans about the connections between food and health. She loves to experiment with healthy recipes in the kitchen and share her creations to inspire others to cook.
Christina completed her dietetic internship at Massachusetts General Hospital and earned her Master of Public Health degree from the University of California, Berkeley. Previously, she graduated with a degree in Ecology and Evolutionary Biology from Princeton University, after conducting her thesis on sustainable agriculture and energy in Kenya. She has done clinical nutrition research at the National Institutes of Health, menu planning and nutrition education at the Oakland Unified School District and communications at the Environmental Protection Agency's Office of Water. She has also enjoyed contributing to children’s gardens, farmers markets and a number of organic farms.