I, lpetrich, envy fungi and bacteria. Many fungi and bacteria are capable of living off very limited selections of biological molecules, sometimes only one kind at a time, like glucose (a simple sugar molecule).
I concede that I envy these organisms. I don’t like having to depend on something like 10 essential amino acids, 2 or so essential fatty acids, and several vitamins. I wish I could be like them, and be able to live off of even the junkiest of junk food.
Most of these nutritional deficiencies are essentially universal across the animal kingdom, as far as one can tell. It must be conceded that nutrition-research taxon sampling across Metazoa has been very limited and patchy. Vertebrates have had the most research, because that’s what we are and what most domestic and lab animals are. The only invertebrates I could find research on is various insects and crustaceans, like the lab fruit fly Drosophila melanogaster. However, they and vertebrates branched away from each other close to the ancestral bilaterian, and that’s not far from the ancestral metazoan.
One can fill some of those gaps by looking at what genes are present in sequenced genomes. KEGG: Kyoto Encyclopedia of Genes and Genomes can show which parts of metabolic pathways are present, and one can deduce whether an organism can make something from what pathway-enzyme genes are present. I’ve perused it a little bit, and its coverage is certainly better. It has some cnidarians and Trichoplax adhaerens, which branched off before the ancestral bilaterian had lived. As far as I can tell, they have the same nutritional deficiencies.
So that’s what happens if you eat lots of high-quality food. You lose the ability to make much of what you need.
If human genetic engineering becomes feasible, it might be possible to insert genes for EAA, EFA, and vitamin biosynthesis, along with whatever regulatory mechanisms would be appropriate. I think that a good place to express them would be the liver, since it does lots of similar tasks. We may need larger livers, but that’s the main side effect.