WASHINGTONUSDAs Nutrient Data Laboratory (NDL) removed the USDA Oxygen Radical Absorbance Capacity (ORAC) Database for Selected Foods from its website due to mounting evidence that shows the values indicating antioxidant capacity have no relevance to the effects of specific bioactive compounds, including polyphenols on human health.
Specifically, the agency said no evidence shows the beneficial effects of polyphenol-rich foods can be attributed to the antioxidant properties of these foods, and data for antioxidant capacity generated by in methods cannot be extrapolated to in vivo effects. USDA also said clinical trials that tested the benefits of dietary antioxidants have produced mixed results.
According to USDAs website, "ORAC values are routinely misused by food and dietary supplement manufacturing companies to promote their products and by consumers to guide their food and dietary supplement choices."
In a response statement to USDA, Ronald L. Prior, Ph.D., who was senior researcher at USDAs Agricultural Research Service (ARS) for more than 30 years where he led research related to phytochemicals and health, said: "It is unfortunate but true that numbers obtained from ORAC analysis have sometimes been misused, but that does not necessarily mean that the information is not useful if used appropriately. In too many cases, the goal has been to obtain the highest antioxidant value. It is not always the case that more is better and in some cases, using individual antioxidant compounds, more may be detrimental."
USDA said the ORAC assay measures the degree of inhibition of peroxy-radical-induced oxidation by the compounds in a chemical milieu. It measures the value as Trolox equivalents and includes both inhibition time and the extent of inhibition of oxidation. Some newer versions of the ORAC assay use other substrates and results among the various ORAC assays are not comparable. However, Prior said ORAC tests have value if comparisons are made using a standardized method, units of expressing the data are clearly defined, and comparisons between different botanicals parts and forms are conducted under full recognition that the values cannot be directly compared.
"Monitoring changes in antioxidant capacity and using other analytical methods to follow individual compound changes during processing of foods is critical to assess and understand what the effects of processing are on the final product," he said. "Most important, ORAC should be used as a complementary analytical tool in the investigative process."
USDA said bioactive compounds may play a role in preventing or ameliorating various chronic diseases such as cancer, coronary vascular disease, Alzheimers disease and diabetes; however, the associated metabolic pathways are not completely understood and non-antioxidant mechanisms, still undefined, may be responsible.
Prior said evidence has shown ORAC tests have been used to show total phenolic consumption may decrease cancer risk. He added in the last three years, more than 25 publications have evaluated dietary antioxidants (polyphenolics) and in vivo antioxidant status or disease.
USDA noted in addition to the ORAC assay, other measures of antioxidant capacity include ferric ion reducing antioxidant power (FRAP) and trolox equivalence antioxidant capacity (TEAC) assays, which also have problems.
"These assays are based on discrete underlying mechanisms that use different radical or oxidant sources and therefore generate distinct values and cannot be compared directly," USDA said.
Brunswick Labs, which conducts antioxidant analysis, said specific comments in USDA's statement are misleading. Brunswick said no in vitro assay quantifies a characteristic of a nutritional product describes in vivo outcomes and should not be used to suggest such a connection. Further, it said vital information about metabolism, bioavailability, mechanisms of action and efficacy is not measured by any such in vitro assay.
Brunswick Labs said polyphenols are connected to beneficial human health outcomes and evidence shows these beneficial outcomes have antioxidant as well as diverse other mechanisms of action. "ORAC has been and remains a valuable analytical tool in connection with other investigative methods," the company said in a statement.