Are chelated minerals worth it?
The question is whether they provide additional benefit to the dog or cat
In the petfood industry, inorganic forms of essential trace minerals such as iron, zinc, copper, manganese, iodine and selenium have been the staple. In recent years, though, chelated forms of these minerals have found their way into a number of petfoods. The questions are whether they provide additional benefit to the dog or cat and if they have a place in petfood.
What are they?
These so-called chelated trace minerals, also known colloquially as organic trace minerals, are purported to be nutritionally superior to the inorganic sources. What makes them different is their ligand. A ligand is an atom or molecule that forms a coordination complex with a central atom or ion. In this case, the ion is the mineral and the ligand is the compound to which it is bound. In their native form, most trace mineral ions are bound to an inorganic anion like an oxide, sulfate or chloride. But for chelated trace minerals, they are bound in a coordinate covalent bond (chelated) to a carbon-containing organic compound like a polysaccharide, short chain fatty acid, protein or amino acid. They are generally synthesized in very strong acid-base reactions under extremes in heat and pressure.
The rationale for adding chelated trace minerals to the diet is to improve mineral availability and animal health. Because of its bond to an organic ligand, the mineral is supposedly more bioavailable. There are a couple of prominent theories as to why this would be; they each focus on the mechanism for uptake of the mineral in the intestine, as either dissociated or intact. Both theories seem to ignore the notion that mineral absorption and utilization are under endocrine control and (or) the animal's mineral status.
One theory suggests the chelated mineral is more available because it breaks apart into its ionic form to facilitate effective absorption. To do so requires a gut pH near the molecule's pKa (the pH at which Â½ the molecule is in the ionic form). The other hypothesis is that the mineral-ligand complex is absorbed intact like a peptide. This theory requires the mineral chelate be taken up by peptide transporters in the gut and it assumes that there is a benefit in efficiency and utilization from pre-formed chelates for cellular functions.
Each theory has been supported with research using model molecules and each has data to support an increased ionic and (or) chelated mineral measured in the circulation. But, does this increase make any difference? Perhaps some. The use of organic trace minerals has been shown to improve markers of hair "health" in dogs and improve puppy litter size. Beyond this, the data in dogs and cats is fairly limited.
Since mineral utilization depends on mineral status, more mineral in the diet doesn't necessarily mean more mineral utilized. For livestock diets in which the emphasis is on cost containment and where mineral fortification may be skirting minimum requirements, a consistent response might be detectable when a more bioavailable form of mineral is provided. However, in petfood applications in which the recommended allowances provide a buffer over minimal needs, and the amount supplied in the food is typically twice the recommended allowance, providing a small increment of a more bioavailable mineral may not necessarily improve the animal's mineral status.
There is a broad array of these chelated trace minerals (or metals) from which to choose. According to the American Association of Feed Control Officials, one can use a metal amino acid complex, metal specific amino acid complex, metal amino acid chelate, metal polysaccharide complex, metal propionate or metal proteinate.
Regardless of which type, they are most commonly merchandised in 50 lb. bags or drums either as the individual trace minerals, e.g., zinc methionine, or blended into a premix. They are commonly free-flowing with a granular to powder consistency and come in a multitude of colors like blue, black, pink, green and white depending on their own particular chemistry. Even though chelated trace minerals often have a distinctive color of their own, they are not likely to be seen in the finished petfood due to their small inclusion level.
On the other hand, trace minerals can lead to discoloration or spotting in some higher moisture foods (such as canned petfoods). We are also instructed to separate minerals and vitamins to reduce fat soluble vitamin losses in premixes. In both circumstances, the issue is oxidation in which transition metals such as iron and copper are involved. Chelated trace minerals have been proposed as a possible solution to these issues. The over-simplistic premise is that since these minerals are bound, they may be less reactive.
But this is an incorrect assumption. Rather, it depends on the redox potential of the molecule (its ability to reduce or oxidize), which is influenced by the ligand. A more neutral salt of the metal will be less oxidative in a petfood, regardless of whether it is chelated. Some of the chelated trace minerals, such as a metal-proteinate, are more neutral and so are less likely to be involved in this oxidation reaction.
The benefits of chelated trace minerals are increased bioavailability of 5-15% and the resolution of some discoloration issues resulting from oxidation. However, they are one-half to one-third the concentration of inorganic trace minerals, and can be more than five times the cost per unit mineral. So the case for their use in petfoods is not overwhelming. Despite this, some petfood companies promote the inclusion of chelated trace minerals individually or in combination with inorganic sources as insurance against the unexpected times when absorption or utilization may be impaired. Under extremes in performance or stress there may be need for the additional level of nutritional support. So they may impart some small benefit to the pet and possibly peace of mind to the pet owner.