Hello, I’m Alex Shin, a pharmacist at Greycoat Research.

At Greycoat Research, we do not recommend just any omega-3 product for cats with CKD. Our concern is simple.

Omega-3 can become rancid during manufacturing, shipping, or storage—before it ever reaches your cat. In one consultation, we worked with the guardian of a cat with CKD in the United States.

Shortly after the guardian started giving the cat an omega-3 supplement from another company, the cat’s inflammatory markers increased.

The cat’s energy and overall condition also declined. We reviewed the recent changes in the cat’s care. The most notable change was the newly added omega-3 supplement.

The guardian took the cat to a veterinarian and stopped giving the supplement. The cat’s condition later stabilized.

We cannot prove that the omega-3 caused the problem, and the product itself was not tested. However, we considered the possibility that the product had been damaged during manufacturing, shipping, or storage and had become rancid.

Since then, we have avoided recommending omega-3 products unless we can verify how they were manufactured, distributed, and stored.

Heat can quickly increase rancidity

In one accelerated storage study, fish oil capsules were stored for 22 days at:

• 20°C (68°F)
• 43°C (109°F)

At 20°C (68°F), peroxide values increased by about 10–20%. Peroxide value is an early test used to check rancidity.

At 43°C (109°F), peroxide values increased in every product tested. In some products, they increased by as much as 241%.[1]

Raw material quality, antioxidants, and packaging all affected the results. The 43°C (109°F) condition was a stress test, not a recommended storage condition.

Even so, the finding was clear. Long exposure to high temperatures can quickly increase the risk of rancidity. Use extra caution with products that may have spent a long time in hot warehouses or delivery vehicles.

Never leave omega-3 inside a hot car. Keep it away from direct sunlight.

High-heat processing also requires caution

Shelf-stable wet food is commonly processed by retort sterilization. This process heats a sealed product under pressure at a high temperature.

In one study of salmon-based wet cat food, conventional retort processing used a target temperature of:

122.5°C (252.5°F)

The full heating and cooling process took about 43 minutes.

TBARS, a test value that rises as rancidity progresses, increased from 0.046 to 0.134 mg MDA/kg.

That was an increase of about 2.9 times.[2]

The final value remained below the study’s threshold for a noticeable rancid taste. Even so, high-heat processing nearly tripled this rancidity marker.

In a separate study, extruded salmon snacks were packaged with nitrogen and made with several antioxidants. 

Even with those protections, a marker of more advanced rancidity continued to increase during eight weeks of storage at:

• 35°C (95°F)
• 75% relative humidity[3]

Seeing “fish oil” or “omega-3” on a label is not enough. What matters is whether the omega-3 remains fresh until your cat eats it.

Multi-use liquid omega-3 requires extra caution

Liquid omega-3 is convenient. 
However, each use may expose the remaining oil to outside air.

One study stored commercial liquid and capsule omega-3 supplements at about 25°C (77°F) under conditions similar to normal daily use.

The highest peroxide values were:

• Liquid products: 44.6C
• Capsule products: 7.62

The highest TOTOX values were:

• Liquid products: 96.94
• Capsule products: 30.44[4]

TOTOX shows the overall level of rancidity in an oil.

The products differed in formula and packaging, so the liquid format may not have been the only factor. Even so, the liquid products showed the highest rancidity markers overall.

Large liquid bottles used over many days require extra caution when their stability after opening has not been tested.

Rancid omega-3 may increase inflammation

Omega-3 is usually given to help manage inflammation. As it becomes rancid, the oil begins to change.

EPA and DHA may decrease.

At the same time, peroxides, aldehydes, and other rancid compounds may increase.

In one mouse study, moderately oxidized omega-3 increased inflammatory markers in the blood and activated inflammatory signaling in the small intestine.[5]

In a canine study, diets containing oxidized fats were associated with:

• Lower blood vitamin E
• Weaker immune responses
• Reduced bone formation
• Reduced weight gain at the highest oxidation level[6]

The canine study evaluated oxidized dietary fats, not omega-3 alone.

Direct long-term studies in cats are still limited.

However, the inflammatory and immune effects reported in other animals give us a clear reason to avoid rancid omega-3. If omega-3 becomes rancid, a product given to help manage inflammation may instead increase the body’s inflammatory burden.

The problem is not omega-3 itself

Cats with CKD may already have higher oxidative stress. One study found plasma F₂-isoprostane levels approximately 3.5–4.2 times higher in cats with early CKD than in healthy cats.[7]

F₂-isoprostane is a marker of fat damage caused by oxidative stress. The same study also reported lower levels in some Stage 1 cats after they were switched to a complete renal diet. Because the study evaluated a complete renal diet, it did not isolate the effect of omega-3 alone.

Still, the main point is clear.

The problem is not high-quality omega-3 itself.

The problem is omega-3 that has not been properly manufactured, transported, stored, or protected from rancidity. For cats with CKD, do not look only at the ingredient list or dosage.

Also ask:

• How was the product manufactured?
• How was it transported?
• At what temperature was it stored?
• Is it protected from rancidity through the final dose?

How Greycoat protects omega-3

At Greycoat Research, good ingredients are only the starting point. We also carefully control how our omega-3 is stored and packaged. According to our warehouse monitoring records, the average storage temperature for our omega-3 is:

20°C (68°F)

The highest recorded temperature has not exceeded:

27°C (81°F)

We monitor the warehouse temperature to limit long exposure to heat. Each capsule is individually sealed in a blister pack. Removing one capsule does not expose the remaining capsules to outside air and humidity.

Remember these three storage rules

1. Keep omega-3 away from direct sunlight and hot cars.
2. Store it in a cool, dry place according to the product label.
3. Keep each capsule sealed in its blister until use.

Storage tip: If your home often becomes warmer than 25°C (77°F), a temperature-controlled wine cooler may help keep the temperature stable.

Use only a cooler that stays within the storage range printed on the product label. Keep the original blister pack inside an airtight container to help protect it from humidity and condensation. Do not refrigerate the product unless the label recommends it.

For cats with CKD, good ingredients alone are not enough

Manufacturing, packaging, distribution, and storage must all be carefully controlled.

For cats with CKD, choose supplements held to strict standards throughout manufacturing, packaging, distribution, and storage.

Thank you,

Alex Shin
Pharmacist
Greycoat Research

Research Sources

[1] Kolanowski W. Omega-3 LC PUFA Contents and Oxidative Stability of Encapsulated Fish Oil Dietary Supplements. International Journal of Food Properties. 2010;13(3):498–511. doi:10.1080/10942910802652222.

[2] Thet TKS, et al. Innovative Ohmic-Assisted Thermal Sterilization: Advanced Thermal Processing of Salmon-Based Wet Cat Foods. Applied Food Research. 2026;6(1):101778. doi:10.1016/j.afres.2026.101778.

[3] Kong J, Perkins LB, Dougherty MP, Camire ME. Control of Lipid Oxidation in Extruded Salmon Jerky Snacks. Journal of Food Science. 2011;76(1):C8–C13. doi:10.1111/j.1750-3841.2010.01896.x.

[4] Yenipazar H, Şahin-Yeşilçubuk N. Effect of Packaging and Encapsulation on the Oxidative and Sensory Stability of Omega-3 Supplements. Food Science & Nutrition. 2023;11(3):1426–1440. doi:10.1002/fsn3.3182.

[5] Awada M, et al. Dietary Oxidized n-3 PUFA Induce Oxidative Stress and Inflammation. Journal of Lipid Research. 2012;53(10):2069–2080. doi:10.1194/jlr.M026179.

[6] Turek JJ, et al. Oxidized Lipid Depresses Canine Growth, Immune Function, and Bone Formation. Journal of Nutritional Biochemistry. 2003;14(1):24–31. doi:10.1016/S0955-2863(02)00221-8.

[7] Granick M, Leuin AS, Trepanier LA. Plasma and Urinary F₂-Isoprostane Markers of Oxidative Stress Are Increased in Cats with Early Chronic Kidney Disease. Journal of Feline Medicine and Surgery. 2021;23(8):692–699. doi:10.1177/1098612X20969358.

[Educational Disclaimer]

This content is provided for general educational and informational purposes only.
It is not intended as a substitute for professional veterinary advice, diagnosis, or treatment, nor is it intended to diagnose, treat, cure, or prevent any disease.
Please consult your veterinarian regarding your cat’s health and before making any changes to your cat’s diet, supplements, or care routine.