When classifying the samples into the three main classes the difference in antioxidant content between plant- and animal-based foods become apparent. The results here uncover that the antioxidant content of foods varies several thousand-fold and that antioxidant rich foods originate from the plant kingdom while meat, fish and other foods from the animal kingdom are low in antioxidants. Comparing the mean value of the 'Meat and meat products' category with plant based categories, fruits, nuts, chocolate and berries have from 5 to 33 times higher mean antioxidant content than the mean of meat products. Diets comprised mainly of animal-based foods are thus low in antioxidant content while diets based mainly on a variety of plant-based foods are antioxidant rich, due to the thousands of bioactive antioxidant phytochemicals found in plants which are conserved in many foods and beverages.

In the nuts and seeds category we analyzed 90 different products, with antioxidant contents varying from 0.03 mmol/100 g in poppy seeds to 33.3 mmol/100 g in walnuts, with pellicle and purchased with nut shell intact. Pecans with pellicle, sunflower seeds and chestnuts with pellicle, have mean antioxidant content in the range of 4.7 to 8.5 mmol/100 g (Table ‚Äč(Table3).3). Walnuts, chestnuts, peanuts, hazelnuts and almonds have higher values when analyzed with the pellicle intact compared to without pellicle.