The Silent Killer (recommendations)

This is part four of a multipart entry on the subject of Chronic Renal Failure in dogs and cats..

The previous three installments of this series have focused primarily on cats and dogs who have already developed chronic kidney disease (CKD). In this final part I would like to focus more on what pet parents can do to mitigate the onslaught of this disease.

The most important thing to understand is that CKD is a progressive disease with no single known cause and is increasingly likely as a pet ages. What pet parents can do is try to mitigate risk factors and be proactive in analyzing their pet's health so as to catch the onset of CKD at the earliest possible moment.


As you now know, protein and phosphorus are problematic for pets that already have CKD. But what about healthy pets?

Begin with phosphorus. It is rare that a diet is too low in phosphorus. The need for phosphorus in the diet grows through the adolescent years and then declines, leveling off at roughly 75% of its peak value. But can a diet be too high in phosphorus?

Perhaps so. though there is no definitive red line for pets or humans and no direct link to CKD. However, elevated phosphorus levels can hinder the effective usage of calcium, iron, magnesium and zinc by the body.

The amount of phosphorus in pet foods is broadly proportional to the amount of protein. Recently, some pet advocates have pushed to have pet food manufacturers increase both the amount of protein and the percentage derived from animal sources in their products.

Like phosphorus, there is no definitive evidence that a high protein diet in otherwise healthy pets will increase the chances of developing CKD. Human studies focus on two areas:

  • increased volume and size of kidney glomeruli
  • an increase in the glomerular filtration rate (GFR hyperfiltration).

Studies in the mid 2000’s were conflicting. One, in The American Journal of Kidney Disease, cautioned that “high protein HP consumption has been found, under various conditions, to lead to glomerular hyperfiltration and hyperemia; acceleration of chronic kidney disease (CKD); increased proteinuria; diuresis, natriuresis, and kaliuresis with associated blood pressure changes; increased risk for nephrolithiasis; and various metabolic alterations.”1

Another study, published in Nutrition & Metabolism, states ”...some studies suggest that hyperfiltration, the purported mechanism for renal damage, is a normal adaptive mechanism that occurs in response to several physiological conditions.” And continues ”...we find no significant evidence for a detrimental effect of high protein intakes on kidney function in healthy persons after centuries of a high protein Western diet.” 2

A more recent study from 2012 found that rats fed a diet of 45% over 12 weeks (said to be equivalent to 9 human years) had significant changes in both the composition and size of their kidneys. Of particular concern was significant drop (88%) in urinary citrate compared to the control group. Hypocitraturia is commonly found in patients with nephrolithiasis - kidney stones.

In addition to the amount of protein, there really is a concern over the move away from mixed sources (i.e., grain and animal proteins) to foods that are all or mostly animal protein. Those foods are higher in phosphorus, sometimes excessively so. Television commercials trumpeting “our food is made from real meat!” sound so appealing and reasonable to pet parents they then refuse to consider better balanced alternatives, often having years of research and testing behind them.

As CKD is ‘the silent killer,’ pet parents must recognize that their pet may already have developed CKD many months, even years, before any formal diagnosis. During that time, the excessive phosphorus found in high protein formulations is accelerating the death of their pet.


The common sense take away from these studies is that excessive protein should be avoided and in the case of dogs, tailored to reflect activity levels. Working breeds (doing work and not watching TV) will require more than more sedentary breeds. There may also be limits to the usable uptake of protein; the figure most often suggested is 35%.

As pets age, pet parents need to be much more focused on phosphorus levels and strive to feed a balanced diet that provides sufficient protein with reduced phosphorus. Because there are so many opportunities for manufacturers to game the ingredient label, I recommend that owners pick up the phone and contact the company to request information about the phosphorus content on a dry or mg/Kcal basis.

Be sure to ask for each variant you may feed your pet - nutritional content for chicken based foods are often dramatically different from those using fish. I also recommend that you ask for sodium content (seeing you are making the call).. As your pet ages, heart related issues may also develop and it is a good idea to avoid products high in sodium (or mix them with others that are low sodium).

By proactively keeping phosphorus uptake under control, the progression of undiagnosed CKD can be mitigated with no harm to pets that never develop the disease.

Testing & Observation

While diet modifications are very important, owners have additional tools to help them fight against CKD. One of the most important is to begin annual blood testing as your pet nears breed based old age. For instance, if your line of Golden Retrievers has a life expectancy of 11 years, you might begin regular blood and urine work at age 7 or 8.

Of course, this will mean additional expense and every pet owner will have a different ability and willingness to pay for testing. It may be possible to begin with just blood or urine and your vet can assist in determining exactly what analysis will be done. Also keep in mind that some vets may be reluctant to ever suggest blood or urine testing be performed unless you indicate your pet has a specific problem. It is up to the pet parent to suggest (or demand) that screening be done. Even a 100% healthy, normal result is valuable as it establishes a baseline against which future tests may be compared.

Owners should also pay regular attention to the frequency and quality of their pet’s urine. If the frequency increases with no obvious reason or the color becomes consistently lighter, seek out your vet. When judging frequency, try to compare not just to recent days or weeks but also prior years. This will help when trying to determine if the increase is due to seasonal variation or may be indicative of a problem.

Ditto for water consumption. If you wake up one morning and say to yourself, ‘hmm.. I’m filling her water dish more often...’ and can’t point to any clear change like a heat wave or change in diet, that too is a reason to contact your vet for examination and additional testing.

Finally, do monitor your pets activity level for signs of lethargy. All too often pet parents (and humans too) attribute a slow down to ‘just old age’. Certainly, a dramatic change is a big red flag. But this is another case where, while you may notice your pet is slowing down and think it normal, one day you realize ‘boy, he’s really slowed down a lot this year.’ Again, get in touch with your vet and express your concerns.

Be proactive!

1. Am J Kidney Dis. 2004 Dec;44(6):950-62

High-protein diets: potential effects on the kidney in renal health and disease

Friedman AN1.

2.. Nutr Metab (Lond). 2005; 2: 25.

Dietary protein intake and renal function

William F Martin,#1 Lawrence E Armstrong,#2 and Nancy R Rodriguez #1

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