Joe Vinson, professor of chemistry at the University of Scranton, evaluated nine types of raw and roasted nuts and two types of peanut butter to assess the total amount of polyphenols found in each.
The study, published in the journal Food and Function, found walnuts had the highest levels of antioxidants and that the quality, or potency, of antioxidants present in walnuts was highest of the nuts analyzed.
"Walnuts rank above Brazil nuts, pistachios, pecans, peanuts, almonds, macadamias, cashews and hazelnuts," Vinson said in a statement.
The study found total polyphenols were considerably lower in peanut butter than in roasted peanuts, Vinson said.
"Nuts are high in fiber, low in saturated fats, high in beneficial unsaturated fats and very high in antioxidants," Vinson said. "Nuts are a nutritious snack and food additive providing both nutrients and bioactive antioxidants which provide significant health benefits to the consumer."