A quick glance at any book titled “metabolism of nutrition” will quickly dispel any notion that animals require only a handful of compounds to live. In fact, they acquire only what they cannot synthesize themselves, namely energy sources, amino acids, minerals and some vitamins. But there are a thousand other compounds they synthesize daily for the organism to function.
Take, for example, betaine. It is needed by the organism (better not ask why!), but we often supply it into animal feeds although the organism is capable of synthesizing it. Why? Is it an essential nutrient? If not, then why do we supply it? If yes, then why there is no official nutrient specification for it?
The same can be said for other quasi-vitamins (for lack of a better term, because voodoo stuff or foo-foo dust are not as professional sounding!) like carnitine, inositol, pteryl-hepta-glutamic acid (I had to look this up!), taurine, lutein, orotic acid, lipoic acid, and the list goes on and on. From an academic point of view, this is a wonderful field of discussion, theorizing and even future funding possibilities. But, for those of us practicing nutrition, what is the current verdict?
I am skeptical. I know some of these quasi-vitamins are absolutely non-essential, meaning adding them into animal feed will confer absolutely no benefit. I am also an optimist (when not cynical). I believe modern animals have been genetically selected to grow/produce faster than their organisms can synthesize some internal compounds. Such is the case with antioxidants, about which I have written extensively. Another one is betaine, which has so many beneficial functions — but only under the right circumstances.
As Dr. Baker used to say, and I love repeating, a Ph.D. is just license to express a (qualified) opinion. I just expressed mine. Feel free to comment with your own!