Per Dr. Michael Greger, author of How Not To Die (https://nutritionfacts.org/):
If we don’t eat phytonutrient-rich plant foods—like fruits and vegetables—with every meal, then, for hours after we dine, our bodies are out of balance and tipped into a pro-oxidative state, which can increase risk of oxidative stress–related diseases. The free radicals in our body can oxidize the fats in our blood, for example, and set us up for heart disease.
Ideally, we should eat as many phytonutrient-rich foods as we can. At the very least, we should eat enough antioxidants to counter the oxidation of digestion (8,000 to 11,000 antioxidant units a day). The average American doesn’t even get half of the minimum recommended daily antioxidants! No wonder oxidative stress–related diseases abound. We’re getting so few antioxidants in our diet that we can’t even keep up with the free radicals that are created when we’re just digesting our meals.
Berries are the most healthful fruits, due in part to their pigments, and are second only to herbs and spices as the most antioxidant-packed food category. As a group, they average nearly 10 times more antioxidants than other fruits and vegetables, and have more than 50 times the antioxidants found in animal-based foods. Including a minimum of a half cup of berries each day is one way to be sure we maximize our antioxidant intake.
Dr. Greger distills down scores of scientific studies done by others to summarize for non-scientists the impacts of various aspects of diet. See our book review of How Not To Die.