Cats’ Hair and Whiskers Suggest a Vegan Diet in Lab Tests — Despite Being Carnivores
Most cat owners know one thing for certain: cats need meat. Unlike humans, they cannot manufacture key nutrients from plant-based foods, which makes them true carnivores. Yet isotope measurements from domestic cat fur suggested something counterintuitive: chemically, they resembled plant eaters more than meat eaters.
In a study published in Frontiers in Ecology and Evolution, researchers at the University of Vienna found that the explanation stems from how cats process and incorporate dietary protein into their tissues. Their results indicate that isotope measurements do not always reflect what an animal actually eats.
“When we tested cats’ hair for nitrogen isotopes, the results made them look like they eat mostly plants,” said first co-author Viktoria Zechner in a press release. “This means that looking isotopically at animal hair alone can sometimes be misleading about their diet.”
Read More: What Cats Are Revealing About How COVID May Linger in the Human Immune System
Tracking Cat Diets With Nitrogen Isotopes
To figure out what animals eat, researchers often turn to stable isotope analysis. Nitrogen, an element found in all living tissue, exists in two stable forms. As energy moves up the food chain from plants to herbivores to predators, the heavier form tends to accumulate.
This pattern is measured using a value called δ15N. In general, higher δ15N levels indicate a higher position in the food web. But tissues do not perfectly mirror food. The difference between the isotope value of an animal’s diet and its body tissues is known as the trophic discrimination factor, or TDF. In many species, this enrichment falls between 3 and 5 parts per thousand.
To see how domestic cats compare, researchers examined fur from 35 indoor cats fed commercial diets. They also analyzed whiskers from 14 of them and measured nitrogen values in supermarket cat food. For comparison, they looked at scalp hair from 653 people who identified as vegans, vegetarians, or omnivores.
Nitrogen Isotope Patterns in Domestic Cats
In humans, the results followed expectations. Omnivores showed higher δ15N values than vegetarians, and vegans showed the lowest values. Cats were different. Their fur and whiskers produced δ15N values closer to those seen in human vegans than in meat-eating humans.
The main difference was the trophic discrimination factor. In human omnivores, there was a sizeable gap between diet and hair isotope values. In cats, that gap was much smaller, averaging around 1.6 parts per thousand.
In practical terms, this means a cat’s fur reflects its food’s nitrogen signature with very little modification.
Researchers believe this may stem from cats’ remarkable efficiency in processing protein. Because their diet consists of animal protein that closely matches their own amino acid requirements, they can incorporate those building blocks into tissues such as keratin with minimal chemical alteration. Fewer metabolic adjustments mean less isotope enrichment.
Humans and many other animals appear to alter dietary proteins more extensively before incorporating them into body tissues. That additional processing tends to increase δ15N values.
Implications for Interpreting Animal Diets
“This does not mean that cats eat like vegans,” first co-author Hannah Riedmüller said. “But it overturns long-standing assumptions about carnivore isotope signatures.”
Stable isotope analysis is widely used to study animal diets, but the study shows that physiology can influence how closely tissues reflect food. In cats, efficient protein use narrows the difference between diet and fur in ways that standard models do not always predict.
The researchers examined only hair and whiskers, leaving open whether blood, muscle, or bone would show similar patterns. The mechanisms behind cats’ low trophic discrimination factor also remain under investigation.
For ecologists, the findings serve as a reminder that isotope values cannot be read in isolation. Understanding how an organism processes nutrients is just as important as knowing what it consumes.
For ecologists, the findings highlight that isotope data must be interpreted alongside biology, not apart from it.
Read More: Cats Rarely Meow at Other Cats — Do They Save Their Voices for Us? Here’s What We Know
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article: