The amino acid taurine is much in the news of late, most recently due to attention from the FDA concerned about heart disease in dogs. Worldwide production of taurine is estimated to be about 5,000 tons, with half of this used by the pet food industry and the balance by the pharmaceutical industry. In fact, taurine has been a topic of concern in cats as far back as the 1970s. One is compelled to ask then, have we learned nothing in the past 50 years? The probability is the feds are just doing their job, gathering data and filing reports, while the media and their audience are generating animated street chatter where calm dialogue would be more appropriate.
A Review of Amino Acids
We were all taught in Biology 101 that the building blocks of protein are amino acids, and that there are 20 of them (or 21, depending on your favorite authority), divided into two distinct categories. There are amino acids mammals are able to build for themselves, using spare parts lying around, and others that mammals can’t assemble and must obtain from their diet. Amino acids required in the diet (because they can’t be made) are referred to as essential, while the others are called nonessential. From here, the plot thickens: the biologic value of a protein is determined by how many essential amino acids it contains. Proteins of high biologic value, such as those from milk, or eggs, have lots of essential amino acids. And of course, proteins of lower biologic value, such as those derived from plants, have fewer essential amino acids.
The amino acid makeup of a protein is like its own personal finger print – a sequence unique to it and determined by a creature’s DNA blueprint. It’s an eloquent, intricate story, often first heard in grade school.
But wait. There’s more. The 20 amino acids pushed to center stage as the building blocks of protein are called proteogenic. But there is far more to the story – that never gets told. As a matter of fact, there are over 500 other amino acids, unheralded and unknown. For example, cadaverine and putrescine, whose origin you can probably guess, are examples of amino acids never encoded into protein by our DNA. Taurine is another, which we’ll get to in a minute. But first a little more background setup.
The Importance of Enzymes
Everyone gets it that ultimately our DNA is in charge, at least concerning fundamental metabolism. And we all listened attentively when told that DNA dictates any and all proteins the body needs. But our metabolism is far more than just proteins. There are endless compounds that are anything but protein. There are carbohydrates, dozens of different types and kinds of fats, countless different mineral compounds, and untold hundreds of molecules that are mixtures and blends of all these non-protein molecules. Did you ever stop to think, where did these come from if they are not protein and not decreed by the only law of the land – DNA? Well, here’s the connection. Yes, our genetic code dictates only protein, but the vast majority of these proteins are enzymes, and these enzymes actually do all the heavy lifting of all metabolism, all the building up of the many diverse tissues types, the crafting of messenger hormones and releasing factors, the assembling of the many different kinds and varieties of compounds in the body. There are compounds as diverse as the mucous lining of the intestine (three types known so far) or the blood in our veins (and the numerous distinct types of blood cells). And just as critical, enzymes mediate the disassembly of things. Think digestion. Life is just a bunch of enzymes – all proteins mandated by DNA.
These enzymes make a lot of sneaky moves that go unnoticed. For example, cartilage contains a unique amino acid that is specific to it and only found in cartilage. That amino acid is hydroxproline. It’s not encoded by DNA. Well then, where does it come from? How does it come to be in cartilage? Enzymes come along later and add the “hydroxy” (with the formula –OH) to the DNA-dictated amino acid proline, making hydroxyproline. Hydroxyproline is one of the more than 500 known amino acids but not one of the 20 rock star protein building blocks. Taurine is similar.
Taurine, the Reluctant Amino Acid
While taurine is an acid, and does contain an amide group, it’s not technically an amino acid in the traditional sense. But taurine is commonplace in mammalian body tissue, including breast milk. The human body can be 0.1 percent taurine, or over 2 ounces (56,000 mg). Taurine production, guided by enzymes, takes place in the pancreas, starting with the amino acid cysteine, a sulphur-containing amino acid.
Taurine is involved in many crucial roles in metabolism. It’s found in bile acids, so is needed for fat digestion. It’s stated to be involved in antioxidation, osmo-regulation, membrane stabilization, calcium signaling (metabolic messenger molecules), essential for cardiovascular function (the DCM of current scrutiny), and needed for proper development of skeletal muscle, retina and the central nervous system. If even some of this is true, taurine is the very definition of essential and really important. Upon reflection, taurine is just as qualified to be classified a vitamin as an amino acid.
Researchers showed in the 1970s that cats fed a plant protein-based diet developed life threatening afflictions (blindness, heart dysfunction) that were reversed if supplemented soon enough with taurine. Since this earlier work, it’s been common knowledge that cats need taurine, that it’s essential to be in their diet, and if not in their diet has to be added as a supplement. I can assure you that for the cat, this was old news, a real no-brainer. Taurine abounds in all meat and meat type tissues. The primordial cat, the feral cat of today, or wild felines of any description do not require taurine supplementation. They are exquisite, consummate predators, so successful as hunters they never lack fresh meat, or the taurine it contains. Now cats on a commercial diet devoid of fresh meat? They will require dietary taurine supplementation, which is far more an indication of a wrong diet rather than something to boast about.
What About Dogs? Is Taurine Good or Bad for Dogs?
It was established 20 years ago that the predominant sign of taurine deficiency in dogs was DCM, dilated cardiomyopathy, or for the layperson, enlarged heart. In people DCM is quite common, with diverse causes, diet being a major one. But cardiovascular disease, such as hardening of the arteries, is not a common affliction of our pets. If enlarged heart occurred in dogs at a similar rate to humans, the FDA would be reporting on millions of cases, not 519. In a recent update to an earlier report, the FDA pointed out that 90 percent of foods being fed when dilated cardiomyopathy (DCM) was diagnosed were grain-free, and 93 percent were diets that contained legumes like peas or lentils.
I have long felt grain free as a market promotion played on pet owner ignorance and misconceptions, in that the real culprit – offending high carbohydrate levels – remained regardless of verbiage. However, the FDA report does not point to source of calories, but rather to some undetermined “anti-metabolite.”
Thus, the latest FDA report would appear to call into question the efficacy of peas and lentils; but to their credit, nobody is judging or pointing the finger. Indeed, FDA and AAFCO are jointly saying, in effect “this is provocative and needs greater understanding.” Part of their reasoning is that data from the market place shows the affliction appearing in various breeds, not just those predisposed genetically. The vet school at UC Davis has long been a leader investigating cat nutrition. That lab is probably the source of the best thread to follow to un-cloak this mystery. In 2002 they published research showing rice bran decreases blood levels of taurine in cats, speculating it bound the taurine and carried it out in the feces. [Stratton-Phelps, et al. 2002. Dietary Rice Bran Decreases Plasma and Whole-Blood Taurine in Cats. J. Nutr. 132:1745S-1747S]. One can’t help but question if similar grain-free ingredients also tie up taurine.
That Dog Won’t Hunt
Be sure you contrast properly the reality at play in this comparison of dogs and cats. Cats can’t make their own taurine and dogs can. The knee-jerk response is to view the cat as handicapped and the dog as more evolved, which isn’t necessarily so. Consider this: compared to the cat, dogs are rather lousy hunters. A long-ago mutation in the dog that allowed them to make their own taurine proved a useful adaptation, covering for their intermittent hunting success. But in its wisdom, evolution saw no advantage for such a mutation for the cat. Why waste precious cysteine to make taurine, when the cat’s diet contained abundant taurine to begin with? It is domestication and wrong diets that handicap the cat.
Don’t Miss the Obvious
Not one case of DCM is being reported by the FDA from pets fed a raw diet. As mentioned, taurine is found in all fresh meat and raw meat diets, especially those that contain organ meats. Further, any diet that is extruded, baked, boiled or canned will have its natural taurine level lowered if not obliterated.
Richard Patton PhD has spent more than 40 years as an animal nutritionist, working in 25 countries and formulating diets for nearly every kind of animal. Based in New Mexico, Dr Patton has consulted for agriculture enterprises, zoos, foreign governments, Fortune 500 companies, local and regional feed mills and pet food companies. An adjunct professor at Penn State for 15 years, he has 25 scientific publications, two patents, one book (on pet nutrition) and numerous popular press articles. Dr Patton’s role in the marketplace is to serve as a translator of technical insight for the benefit of the animal and the animal owner. He is the author of “Ruined by Excess, Perfected by Lack,” a second edition of which was published by Dogs Naturally in 2017 and reprinted in 2018.