Free radicals support human health. If in excess, however, they can alternatively cause oxidative damage to cells and contribute to aging or even the development and progression of degenerative diseases.
Fortunately, evidence indicates that antioxidant substances may help combat excessive free radical production in the body. Normally, the body maintains a balanced production of free radicals and antioxidants. But when free radical production overwhelms the body’s antioxidant supply and hence its ability to temper free radical bioactivity, some other intervention is needed. This is where dietary antioxidants come into play.
While exogenous dietary sources of antioxidants do not have a direct effect on tempering free radical overproduction, these sources can help stimulate increased production of antioxidants within the body—to the point that balance between free radicals and antioxidants is restored.
In recent decades, much effort has been invested in identifying dietary substances of high antioxidant potential. As part of these efforts, analytical methods, or assays, have been developed specifically to measure the antioxidant content in food substances.
Without a doubt, the assay most publicized thus far has been the oxygen radical absorbance capacity (ORAC) assay. ORAC is a robust analytical method that emerged more than two decades ago, developed by scientists working at the National Institutes of Health (NIH) and USDA.
The ORAC assay determines the antioxidant potential of foods, botanicals, and biological samples. It is an in vitro test that can measure to what degree a substance of interest can scavenge various free radicals.
Importantly, ORAC cannotbe used to predict what effect or benefit an antioxidant substance will have within the human body in attenuating free radical production or coping with oxidative stress. As an in vitro test, ORAC cannot predict such in vivo effects—nor can any other chemical assay.
Over the past few decades, ORAC has seen both skyrocketing popularity as well as sharp criticism over whether it is a valuable assay at all—especially in light of newer assays. In this article, we discuss the rise, the fall, and the promise of ORAC.
How ORAC Began
ORAC started as a brainstorm in the 1980s between two USDA scientists commuting to the same lab in Boston. One of the commuters, a noted neuroscientist named Jim Joseph, PhD, had focused his laboratory studies on antioxidant-rich foods, such as blueberries, cranberries, strawberries, walnuts, and acai. Dr. Joseph mentioned to his fellow USDA commuter Ronald Prior, PhD, that he needed a way to determine the free radical–scavenging capacity of foods because he believed some foods might contribute to delaying the development of certain neurodegenerative diseases. First, Dr. Joseph needed a validated and precise way to measure free radical–scavenging capacity.
The ORAC assay was ultimately invented by Guohua Cao, MD, PhD, at NIH’s National Institute on Aging in Baltimore. Dr. Cao then developed the assay in the lab of Dr. Prior and Richard Cutler, PhD, at the Jean Mayer Human Nutrition Research Center on Aging at Tufts University, Agricultural Research Services, USDA.
USDA realized early on that the ORAC assay could be used to determine which fruits and vegetables have high antioxidant potential—and consequently might protect consumers against certain diseases. There was also a growing understanding that certain compounds—beyond just vitamins C and E or beta-carotene in fruits and vegetables—have strong antioxidant capacity. Scientists soon became very interested in measuring the antioxidant capacity of a range of fruits and vegetables to determine which ones people should eat in order to lower their risk of diseases associated with free radical pathology.
By 1991, the first version of the ORAC assay caught the attention of food scientists.1 Two years later, the assay was modified, automated, and capable of measuring antioxidant capacities of biological samples.2 By 1999, an improved and validated ORAC assay was developed—and continues to be the standard by which labs perform this assay around the world today.3
What Is ORAC?
The ORAC assay can quantify the scavenging activity of a food, compound, or agent to a single free radical anion, the peroxyl radical. This peroxyl radical is the most abundant free radical produced in the human body. Under conditions of oxidative stress, and due to a failure of indigenous antioxidants to stop its production, peroxyl radical levels can rise and damage cells and tissue—kind of like a “fender bender” on the freeway that just keeps hitting one car after another, for miles.
The improved ORAC assay introduced in 1999 relies on a common fluorescent probe, fluorescein, to monitor antioxidant activity. A microplate reader capable of detecting fluorescence can perform the assay in a 96-well or 48-well microplate format. This allows the ORAC assay to test many substances within a short period of time. Due to ORAC’s low cost and reproducibility between labs, the assay became a favorite of food scientists as they sought to identify foods with higher levels of antioxidant compounds. ORAC’s intra-assay precision made it particularly useful as a starting point for determining whether a substance might have characteristics able to attenuate free radical pathology.
The ORAC assay has further evolved over time. For instance, as scientists gained more understanding of the variety of free radicals in the human body, it became necessary to determine the scavenging activity of the five major radicals produced in the human body: hydroxyl radical, peroxyl radical, peroxynitrite, singlet oxygen, and superoxide anion. When at normal levels, these five free radicals play an essential and vital role in supporting the immune system’s ability to kill pathogens such as bacteria. However, when overproduced, they not only harm pathogens but also healthy cells. Keeping production of these five free radicals within a desirable range to support immune function is critical. In 2009, a new version of the ORAC assay was developed to quantify the scavenging capacity of all five important free radicals, individually or in combination. When the scores are combined, the resulting number offers scientists a Total ORAC for Food and Nutrition (TOTAL ORAC FN) unit value per gram. (Read more on this Total ORAC assay in the sidebar below.)
The Rise of ORAC
By the beginning of this century, USDA decided it could use ORAC to test virtually every food in the American diet—particularly foods suspected of having high antioxidant capacity, such as fruits, vegetables, and nuts. Within a few years, the results of such testing appeared in a series of papers published in various nutrition journals.
USDA used these results to build—and, in 2010, to publish—an independent, non-commercial database of verified ORAC scores for hundreds of foods. Notably, USDA made sure that its process for gathering food for testing reflected the way consumers obtain their food in the real world5—that is, USDA purchased foods in the marketplace just as consumers would do. Foods were selected during different seasons and in different forms (jellies, juices, purees, etc.). Each food item was then sent to a central USDA lab, freeze-dried (if purchased fresh) to remove almost all of its moisture content, and forwarded to another USDA lab where experienced chemists performed the ORAC assays. In this way, the ORAC value of each food was added to USDA’s ORAC database.
As ORAC captured public attention, companies began citing ORAC values to market their products’ antioxidant benefits, believing consumers assume that a product with a higher ORAC score is better than a product with a lower score. Hence began what some called the “ORAC race,” with companies striving to pit their products’ ORAC values against their competitors’.
As ORAC competition grew fierce, some of the most dubious ORAC claims I noted in the marketplace at the time came from ingredient suppliers at industry trade shows. For example, at a trade show, several ingredient firms marketing maqui berry (Aristotelia chilensis) displayed bar graphs promoting the berry as having a significantly higher ORAC score than such USDA-tested foods as acai, cranberries, and wild blueberries. When I asked the ingredient suppliers for the substantiation supporting these claims, one company merely responded that its product is a “maqui complex,” whatever that means.
Another ingredient supplier failed to realize or specify that USDA reports ORAC values in per gram measurements. As such, the ORAC assay result displayed on the company’s bar graph in marketing materials actually represented ORAC values per 100 grams; thus, the maqui product being promoted actually had an ORAC score that was 1/100th the ORAC value being touted. But when I asked that company to disclose the published scientific journals from which it had obtained the ORAC score claimed for its maqui, the company said the results had not been published but instead were obtained from ORAC testing performed by a leading laboratory. After the trade show, I contacted that laboratory and asked it to verify the results the ingredient supplier reported. The laboratory said the numbers the company used did not reflect the assay results the lab had provided—and, moreover, that the results the laboratory had provided did notreport ORAC values per 100 grams, as the company’s graph indicated.
To one company’s credit, upon being alerted to its errors, the company promised to immediately remove the bar graph from its booth. Still, I can remember seeing a professor of nutrition from Chile who had seen the display expressing frustration on the trade show floor about such misleading information, stating that this kind of misinformation only hurt the image and reputation of an otherwise nutritious food.
As manufacturers became convinced that products needed a high ORAC value in order to sell competitively, and companies began leveraging their ORAC numbers to infer products were somehow superior, some unscrupulous firms even resorted to spiking products with antioxidants simply to increase their ORAC score. Additionally, laboratories began reporting extraordinarily high ORAC scores. When questioned on whether or not products may have been antioxidant-spiked, many contract laboratories pointed out that they had merely been asked to perform the ORAC assay, not characterize the product for the presence of any undeclared antioxidant agents that could have significantly raised the score.
Other cases of misleading data occurred when companies made questionable comparisons of the ORAC values of dietary supplement ingredients and the ORAC values of food ingredients. For example, a company claiming that consuming a gram of its supplement was equivalent to consuming 10 fruits and vegetables had intentionally selected fruits and vegetables in the USDA ORAC database that had very low ORAC values, such as a head of lettuce and a watermelon. Obviously, this is not the fairest or most honest comparison.
As companies competed on ORAC values, companies whose products have lower ORAC scores—such as goji or mangosteen—had to vie for the attention of consumers who had become very interested in foods with high ORAC scores, such as acai, blueberries, strawberries, and cranberries. These companies soon realized that consumers were spending their dollars on foods with higher ORAC scores. Frustrated, these firms began raising questions about the utility and value of the ORAC assay. In part—and rightfully so—the companies pointed out that foods have other beneficial attributes beyond antioxidant capacity alone, such as anti-inflammatory bioactivity.
As these critics spoke out, questions and controversy surrounding ORAC grew. Scientists became concerned that too much marketplace emphasis was being placed on ORAC scores alone. After all, they pointed out, ORAC is an in vitro test, and its results cannot automatically be assumed indicative of any in vivo benefits when a food substance is in the human body. Although the layman consumer might not understand this crucial point, ORAC in fact was not established to predict whether a high-ORAC food or compound will have a high level of free radical scavenging activity in the human body. For instance, a review paper on antioxidant assays appeared in a noted scientific journal stating: “Any claims about the bioactivity of a sample based solely on assays such as ORAC, TEAC, and FRAP, etc., would be exaggerated, unscientific, and out of context. Moreover, these assays do not measure bioavailability, in vivo stability, retention of antioxidants by tissues, and reactivity in situ.”8 The authors of that review paper concluded that assays such as ORAC, TEAC, and FRAP “bear no similarity to biological systems” and that how the compounds impact endogenously produced antioxidants cannot be seen in a lab assay; reactions or benefits observed during oxidative stress cannot be measured in the lab.
And, as the number of in situ in vivo studies (somewhere in between in vitro and in vivo studies) of foods or nutraceutical products progressed, it became evermore apparent that the ORAC score of a food or compound does not always predict the degree to which a compound may be beneficial in the body.
As the scientific community grew frustrated by the marketplace overemphasis on ORAC, it eventually sparked a warning from scientists to those using ORAC numbers in the marketplace to be careful not to oversell or misrepresent what ORAC means. They urged marketers to use ORAC numbers responsibly.
Such warnings were issued to industry as early as 2004, including by myself and Ginny Bank in an article written for industry trade journal Nutraceuticals World.6 In that article, we provided the industry with a critical review of the strengths and weaknesses of the ORAC assay, pointing out that “with competitive use of ORAC values comes misconceptions and misuse.”
As we predicted, it did not take long before the marketplace became confused as to what ORAC numbers actually mean. The article we wrote forewarned that the “future of ORAC or any antioxidant assay will depend upon the responsible use of results when making comparisons.”7 The article also reminded the dietary supplements industry that “DSHEA clearly states that in advertising and marketing the ‘truthful and misleading’ yardstick should rule the day when making antioxidant unit comparisons.”
We also forewarned, “If comparisons are made, let them be made on the basis of sound analyses; otherwise the nutraceutical industry risks destroying the currency of ORAC in the minds of consumers as its value in product comparisons grows.”
Indeed, fast-forward, and today criticisms of ORAC abound. Many have come to question whether ORAC is a useful analytical method at all.