The current trends in food and medicine uses preformed chemical products that are readily absorbed by the body. Most of these chemical compounds are purified like all forms of vitamins, minerals, anti-biotic, and other drugs that when ingested are directly absorbed from the stomach to the liver then to body parts that need them.
However, viewing from the normal and natural processes within the body, the one originally designed by God, or "nature" for the unbeliever's viewpoint, using preformed chemicals for use of the body nutrition and repairs bypasses some important pathways that generate intermediary chemical products that are also useful in a lot of body processes.In the normal metabolic processes of the body. Basic nutrients such as glycogen, amino acids, fatty acids, and micro nutrients like vitamins, minerals, and other chemical compounds are being produced through metabolic pathways before they are stored then utilized in the body systems. Take for example the case of vitamin A. In plants vitamin A does not exist as pre-formed Vitamin A. The body systems break down the complex carotenoids from the plant materials until retinol (Vit A) is produced. At some point within the metabolic pathway intermediate products come out. In our example, beta-carotene, is a simpler carotenoid, but prior intermediate compounds are also synthesized and reactant compound existing in the body combine with the chemicals to produce other intermediates until finally reaching the final form. Within the process, intermediate compounds are not fully mixed up to form the final products, instead some are used in other useful body metabolic pathways such as synthesis of other important body chemicals, hormones and others.
When a person rely on the consumption of preformed vitamin A to supply body requirements instead of consuming materials that contain them, example vegetables and fruits, that person deprives its body system with the needed intermediaries. Beta carotene has a unique function separate to what retinol can do in the body, so that when you take retinol directly, you have no chance of accessing beta-carotene but take them separately.
The retinol and beta-carotene illustration is just one of the simpliest example of what I'm trying to explain. But the bodies metabolic pathways are so complicated, more complicated than solving mathematics problem. It is for scientific studies to gather enough evidence of the importance of intermediate products so that taking pre-formed nutrients should not be recommended.
Let God be praised by how perfect His creation is and let no man play and modify His systems.