Hello, I’m Dr. Hocheol Shin, or “Dr. Shin.” I study feline kidney health and aging at Greycoat Research.

I earned my Ph.D. studying cancer and immunology, and I’m now building on that experience to explore how we can help cats stay healthier for longer.

In “Reading Papers with Dr. Shin,” we’ll explore research related to feline health together. We’ll look a little deeper into how things work, what the studies actually found, and what those findings might mean for our cats. I’ll explain any unfamiliar terms as we go.

Ready to open today’s paper with Lulu?

Three-Sentence Summary

1. In a study of healthy older cats, the older age group had lower lean body mass and lower kidney filtration, yet also had lower creatinine.
2. Some circulating metabolites changed with the dietary conditions, but changes in kidney function markers were not demonstrated over six months.
3. When evaluating ingredients and products at Greycoat Research, we need to distinguish “Which measurements changed?” from “What actually improved for the cat?”

Introduction: Should a Lower Number Always Be Reassuring?

We are used to hearing about rising creatinine in discussions of kidney disease. It is understandable that a lower number might feel reassuring.

But does a cat with lower creatinine necessarily have better kidney function?

Today’s paper contains a finding that makes us reconsider that assumption. The older group of cats had lower filtration, but lower creatinine as well.

The number on its own might look favorable. The function measured alongside it did not support that simple interpretation. Let’s look at why those findings need to be read together.

Background: Less Left in the Blood, or Less Produced?

Creatinine is produced mainly in connection with muscle metabolism and is cleared through the kidneys. Interpreting its blood concentration therefore means considering two sides: how much is cleared and how much is produced.

If we think only about clearance, a lower concentration can look like a better result. But differences in muscle mass can also affect the production side of the picture.

The paper also uses the term “lean body mass.” This refers to body tissue mass excluding fat. Muscle is included, but it is not a measurement of muscle alone. We should not automatically turn a finding about lower lean body mass into an identical statement about changes in muscle mass.

Keep those two points in mind as we compare body composition, measured filtration, and blood test results.

The Study: Examining Diet, Body Composition, and Kidney Function Together

Hall and colleagues published this study in The Veterinary Journal in 2014. It involved 32 healthy cats with a mean age of 14 years.

The cats ate a control food or one of two experimental foods for six months. The researchers collected blood measurements, measured glomerular filtration rate (GFR), and assessed body composition.

The experimental foods included added fish oil and L-carnitine. One also differed in medium-chain fat and other dietary conditions. In other words, this was a comparison of foods that differed in several ways, not an isolated test of a single ingredient.

We’ll read two sets of results separately: the comparison between age groups and the changes associated with the diets.

First Finding: Lower Filtration and Lower Creatinine

Cats older than 15 years had lower lean body mass and GFR than cats younger than 12 years. Yet their creatinine concentrations were also lower. SDMA, by contrast, was higher.

This is the finding that most caught my attention. Looking at creatinine alone, we might have interpreted the lower number favorably. Putting filtration and body composition beside it makes that interpretation much less straightforward.

I would not jump from this to, “Creatinine was lower because aging caused muscle loss.” These were comparisons between different age groups, not measurements tracking how much creatinine fell as an individual cat lost muscle. The distinction between lean body mass and muscle mass also matters here.

Even so, the practical point is clear. In this comparison, lower creatinine did not mean better filtration. That is a reason to consider the cat’s physical condition when interpreting the number.

Second Finding: A Biological Response Is Not Necessarily Better Kidney Function

The dietary comparisons showed changes in circulating fatty acids and carnitine-related metabolites, among other measurements. But changes in kidney function markers were not demonstrated over six months.

Those are separate findings. Whether an ingredient or diet produces a measurable response in the body is one question. Whether that response translates into a difference in kidney function is another.

A change in metabolites can still be informative. It may point to a response worth studying further. But rewriting that finding as “kidney function improved” would say more than the measurements established.

It also matters that the study involved healthy cats. These findings cannot be directly presented as treatment effects in cats with chronic kidney disease. And because several dietary conditions differed together, we cannot attribute the findings to a single ingredient with certainty.

Personal Thoughts: Are We Protecting the Number or the Cat?

I think this paper raises an important question about how we explain nutritional ingredients and products.

Before saying that “the numbers improved,” we need to specify which measurements changed and in which direction. Then we need to examine how those changes relate to the function or physical condition we are trying to preserve. A number falling is not, by itself, enough to conclude that something improved.

Maintaining kidney filtration, supporting adequate food intake and physical condition, and examining longer-term outcomes are connected goals, but they are not interchangeable. We need to define what we are evaluating before interpreting the result.

That is also part of the product philosophy I consider important at Greycoat Research. An ingredient name or a proposed mechanism is not the end of the story. We need to connect it with what actually changed for the cat. A change in a metabolic marker should be described as such; a change in function needs evidence of a change in function.

Today’s study is not proof that a particular nutritional ingredient, or our product, treats kidney disease. To me, it is a reason to be more exact about what we call an improvement. We are trying to protect not just a number on a lab report, but the cat that number belongs to.

In the first three articles, we examined damage inside the kidney. In this group, we considered blood results, weight, and body composition. Next, we move to “The Carnivore’s Bowl.”

We often hear that diet is important in managing kidney disease. What did studies in actual cats find that made renal diets an important part of management? In the next article, we’ll follow the outcomes of cats fed those diets.

The findings discussed in this article reflect associations, mechanisms, and early translational evidence rather than confirmed efficacy in cats with kidney disease. Please consult a veterinarian before starting any supplementation protocol.

References

1. Hall JA, Yerramilli M, Obare E, Yerramilli M, Yu S, Jewell DE. Comparison of Serum Concentrations of Symmetric Dimethylarginine and Creatinine as Kidney Function Biomarkers in Healthy Geriatric Cats Fed Reduced Protein Foods Enriched With Fish Oil, L-Carnitine, and Medium-Chain Triglycerides. The Veterinary Journal. 2014;202:588–596.

About the Author

Hocheol Shin, Ph.D. Greycoat Research

B.S./M.S./Ph.D. in Biological Sciences, KAIST (Korea Advanced Institute of Science and Technology)

Research background in cancer immunology, tumor microenvironment, and translational oncology. Currently engaged in companion animal health and longevity research.

Educational Disclaimer

This article is for educational purposes only and is not a substitute for professional veterinary advice, diagnosis, or treatment. It is not intended to diagnose, treat, cure, or prevent any disease.

Please consult your veterinarian before making changes to your cat’s diet, supplements, or care routine.