Most studies on bioavailability of phenolic antioxidants are focused in foods and beverages in which they may be easily released from the food matrix, reaching a peak in plasma antioxidant capacity 1–2 h after the intake. However, plant foods contain significant amounts of polyphenols associated with dietary fiber. The aim of the present work was to seek the bioavailability of total phenolic antioxidants associated with dietary fiber by measuring plasma antioxidant capacity in human volunteers. An acute intake of 15 g of a dietary fiber rich in associated phenolic antioxidants in healthy volunteers (n = 10) increased antioxidant capacity of plasma in relation to a control group (n = 4), becoming significant 8 h after the intake. This shows that phenolic antioxidants associated with dietary fiber are at least partially bioavailable in humans, although dietary fiber appears to delay their absorption. No significant changes were observed after long-term intake (16 weeks, 34 subjects).