Tuna is a cat’s favorite food, but why do they love a deep ocean fish that would never be found in the wild?
Almost no food is as proverbially popular with cats as tuna. But it’s curious, because cats evolved on land long before canned fish were invented. Now, however, at least part of the explanation for this unlikely preference emerges.
The research group led by Scott J. McGrane, from the Waltham Petcare Science Institute in the United Kingdom, discovered that cats’ taste receptors react especially strongly to two substances that tuna contains in large quantities. As published in the journal Chemical Senses, cats prefer this combination of the amino acid histidine with the nucleotide phosphate of inosine in taste tests. However, it is still unclear why these substances have such a strong effect on cats.
In reality, the result is only a secondary finding of the study. The goal of McGrane’s team was to demonstrate that cats can perceive the taste of meat as umami, a reasonable assumption for a carnivore, but not yet proven. In many animals, and also in humans, two receptor proteins work together to produce the sense of umami taste, encoded by the genes Tas1r1 and Tas1r3. They detect a combination of amino acids, which make up proteins, and nucleotides, the building blocks of RNA and DNA. Amino acids, especially glutamate and aspartate, activate umami receptors, and nucleotides amplify the signal.
Until now, it was only known that cats have the Tas1r3 gene, that is, half of those necessary to detect umami. Therefore, the research group analyzed which genes were active in the tongue of a cat that had been euthanized for health reasons.
In addition to Tas1r3, they found Tas1r1, and research on the two proteins showed that cats can indeed taste umami with them. However, the team also discovered crucial differences with human umami receptors.
The binding site to which the amino acids glutamate and aspartate attach, especially activators in humans, is mutated in cats. As a result, according to McGrane, the receptors work exactly the opposite than in humans. It is not the amino acids that provide the activating signal, but the nucleotides.
Taste tests show that this difference does not change the fact that cats generally perceive and prefer umami flavors. However, it leads them to prefer completely different substances. While glutamate stimulates the umami sense more in humans, in cats it is inosine phosphate and histidine, which are found in especially large quantities in tuna. What is not clear is whether this connection has an evolutionary function. It is possible that the preference for fish has been advantageous in coexistence with humans. On the other hand, it is likely that the connection between the cat’s taste receptors and tuna meat is a mere chemical coincidence.
Also Read | 15 best science experiments for kids to do at home
