Reducing compounds from plants are abundant in our diet, especially phenolic compounds (polyphenols). They are too often termed antioxidants whereas this notion remains fuzzy and open to abuse. Polyphenols and other reducing micronutrients can actually participate in the protection of polyunsaturated fatty acids (PUFAs) against oxidation, not only in foods (including as additives) but also in the digestive tract. This aptitude can be summarily evaluated by the total antioxidant capacity (TAC) but must be confirmed in more elaborate tests involving PUFAs. By contrast, crediting them with an antioxidant activity in tissues (beyond the digestive tract) on the sole basis of a high TAC value is abusive, on the one hand because fighting chronic oxidative stress via a plant-rich diet involves a great variety of mechanisms and remains tightly associated with anti-inflammatory actions, on the other hand because polyphenols generally undergo extensive catabolism by the intestinal microbiota and are distributed to tissues under the form of metabolites whose structures are very different from those of the dietary forms.