Once animals could also synthesize some antioxidants, including vitamin C. But the rich plants nourishment of our ancestors content so much vitamin C that we lost in time this ability to produce this composite, maybe because of the natural selection which tends to give any unnecessary element up that is metabolically costly. (Plants are a rich source of antioxidants because they need those for the oxygen management, produced during the photosynthesis)

Of course this was a great evolution for plants, because people have become completely dependent on them for procurement of an essential nutrient and therefore, people did those vitamin C producers lots of favors, spreading there genes and extending there habitat. The antioxidants like vitamin C has an important role in the relationship between humans and plants even this is less noticeable. Our biologically plant dependency is ancient and profound, so it’s not at all surprising that plants are beneficially.
There are many studies which are proving that rich nourishment in fruits and vegetables is reducing the risk of death in case of all occidental diseases. In countries where people consume daily a pound ore more of fruits and vegetables, the rate of cancer is twice smaller then in the United States. We also know that vegetarians are less disposed to all the occidental diseases and therefore they live longer (semi-vegetarians the so called “flexitarians”- are as healthy as vegetarians). We do not know very well why this happens. It is almost sure that the plant antioxidants protect us, but this could be valid for omega-3 fat acids (other essential nutrients which our body can not produce) for fibers and for other elements and synergic relations of plants compositions, unknown jet.

As shown on the studies of whole grain it is very possible that vegetal aliments are more than the amount of composing nutrients. But probably the advantages of plant based nourishment aren’t based only on the content: vegetal products (with the exception of seeds) have the energy density lower then the rest of nourishments. Eating especially veggies you will consume probably less calories (which will protect you from many diseases). Seeds are the exception that shows us why it is important to consume more leaves then seeds; even if unrefined seeds like whole grain and fruits with a hard shell can be very nutritious, they contain more calories, because there biological role is to deposit energy.