In vitro testing of antioxidant capacity for a wide variety of foods, commonly known as oxygen radical absorbance capacity, has become marketing shorthand for products claiming “superfruit” status or a role as an “antioxidant superpower.” But using ORAC for comparative marketing purposes is deceiving, as the revised ORAC fluorescein method gives about double the ORAC value of the old phycoerythins method. Comparisons are also unfair when based on a “per gram” basis, as this favors spices and dried fruit over fresh fruit and fruit juices. For example, dried Tibetan goji berries are reported as having 10 times the antioxidant content of fresh blueberries.
Another problem: Any claims for “my ORAC is bigger than your ORAC” need to take into account exactly what ORAC methods were used for the products being compared. In 2009, Brunswick Laboratories introduced Total ORAC FN as a patented measurement of antioxidant activity against five free radicals: hydroxyl, peroxyl, peroxynitrite, singlet oxygen and superoxide anion.
Regardless of method, in vitro measurement of antioxidant activity doesn’t address limited bioavailability for many of the larger polyphenols, nor the fact that smaller molecules are metabolized so quickly that no trace of the unaltered molecule can be found in the blood.
Claims for relevant biomarkers also have problems. Reporting a higher plasma antioxidant capacity after eating an antioxidant food or taking a supplement does support the idea that compounds are bioavailable and retain at least some of the purported chemical activity. However, without any connection to a clinically relevant outcome, this is not sufficient to support a health claim. The ex vivo assay demonstrating increased resistance of low-density lipoprotein to oxidation is in the same boat.