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. Early research found that the activities of several liver enzymes changed little when cats ate diets with different protein levels.
2. Later measurements of whole-body metabolism found that the amount of protein used for energy did change with intake.
3. At the lowest protein intake, however, cats lost body protein. Being able to adjust does not make every low intake adequate.

< Getting Started >

Cats need substantial amounts of protein. One explanation often follows:

“Even when cats eat less protein, they cannot slow its breakdown.”

Does that mean a cat keeps using the same amount after its protein intake falls? The research is more interesting than that simple account suggests.

An early study measured liver enzymes. A later study measured how much protein cats actually used for energy across the whole body. They were measuring different things.

< Having the Machinery Is Different From Using It >

Enzymes are proteins that help chemical reactions take place. The liver contains enzymes involved in processing amino acids and making urea.

Think of enzymes as machinery in a factory. Keeping the same machines does not mean producing the same amount every day. Actual output can change with the incoming materials and operating conditions.

An enzyme activity assay measures how much of a reaction an enzyme can support under specified conditions. Whole-body protein oxidation measures how much protein is actually used as fuel. One describes the machinery’s capacity; the other describes how much work it is doing.

< First, Researchers Looked at Liver Enzymes >

In 1977, Rogers and colleagues fed adult cats diets with different protein levels and measured several liver enzyme activities. Most changed little, including enzymes involved in the urea cycle.

This helped support the idea that cats regulate protein metabolism differently from some other animals. It also became part of the explanation for their high protein requirements.

But relatively unchanged enzyme activities do not establish that actual protein use cannot change at all. That required measurements across the whole body.

< Actual Protein Use Did Change >

In 2008, Green and colleagues fed nine healthy adult cats four diets in sequence. Protein supplied approximately 7.5%, 14.2%, 27.1%, or 49.6% of metabolizable energy. These percentages refer to energy, not the proportion of the food’s weight that was protein.

The researchers measured respiratory gases and nitrogen excretion to calculate how much protein was being used for energy.

Protein oxidation changed with the diet. Cats used more protein for energy when intake was higher and less when intake was lower. They were not completely unable to adjust whole-body protein use.

< The Lowest Intake Still Caused a Loss >

The diet providing 7.5% of energy from protein was different. Although cats reduced protein oxidation, they still used more protein than the diet supplied. They experienced a net loss of body protein.

It is like reducing spending when income falls, but still spending more than comes in. Adjusting expenditure does not necessarily eliminate the deficit.

The conclusion therefore has a condition: cats could adjust protein oxidation to intake when their dietary protein requirement was met. At an inadequate intake, that adjustment did not prevent protein loss.

These were healthy adult cats. The experiment did not establish the best protein intake for cats with kidney disease.

< Personal Thoughts >

Reading these studies together changes how I explain what cats are like. They have high protein requirements, but their bodies are not incapable of adjusting when intake changes.

There is no need to dismiss the early study as wrong. Several liver enzyme activities can remain similar while whole-body protein oxidation changes. Both observations can be true because the measurements answer different questions.

For feeding, the final part is especially relevant: the ability to adjust still depends on receiving enough protein. That brings us back to the previous article’s discussion of protein management alongside adequate nutrition.

So far, we have focused on protein. There is another number on the food label that matters in kidney disease: phosphorus. Is choosing the lower number enough? Next, we look at both how much phosphorus a food contains and the form in which it is supplied.

< References >

1. Rogers QR, Morris JG, Freedland RA. Lack of hepatic enzymatic adaptation to low and high levels of dietary protein in the adult cat. Enzyme. 1977;22:348–356.
2. Green AS, Ramsey JJ, Villaverde C, et al. Cats are able to adapt protein oxidation to protein intake provided their requirement for dietary protein is met. Journal of Nutrition. 2008;138:1053–1060.

< 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.