When I was growing up, my father grew tomatoes in our backyard. As plants grow, the new growth is made from materials taken from the soil. Nothing can be incorporated into plants unless it is present in the soil. Plants grown in depleted soils are just not the same. Commercial fertilizers can add the basic, required minerals back into the ground, but this simplified soil is not as rich as organically maintained soil.
Plants do the best they can with whatever materials are available.
Today, as I write, she is 8 years old and weighs over 50 pounds. All of the materials for this dramatic increase in size have come from the food she has eaten. Like the tomato plant, Claire's body does the best it can with available materials. When I look at my children playing football in the park, I am looking at structures built from the food they have eaten, the composition depending on the nutrients that were available at the time. Getting children to eat well, though, is far easier said than done.