Fish Oil Isn't What You Think: How EPA and DHA Reprogram Inflammation in Dogs

By Steve Mehler, DVM, DACVS

For decades, omega-3 fatty acids have been recommended for dogs with osteoarthritis, skin disease, kidney disease, heart disease, and cognitive dysfunction. Most veterinarians—and certainly most pet owners—understand that fish oil is "anti-inflammatory."

But that's only part of the story.

The real biology is far more fascinating.

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) don't simply reduce inflammation. They influence how cells behave, how genes are expressed, and even how the body knows when it's time to stop inflammation and begin healing. In many ways, they act less like a supplement and more like a biological signaling system.

EPA and DHA Don't Change DNA—They Change Gene Expression

One of the biggest misconceptions about nutrition is that food only provides energy or building blocks. In reality, nutrients can also serve as molecular signals.

Think of EPA and DHA as genetic dimmer switches, not genetic rewriters.

They don't alter a dog's DNA sequence. Instead, they influence which genes are turned on, which are turned off, and how strongly those genes are expressed. 

When EPA and DHA enter cells, they interact with proteins called transcription factors, which act as master switches controlling hundreds of genes simultaneously.

One of the most important families of transcription factors is the PPARs (Peroxisome Proliferator-Activated Receptors).

When activated by EPA and DHA, these receptors move into the cell nucleus and alter gene expression. The result is increased expression of genes involved in:

• Fat burning

• Mitochondrial function

• Lipid transport

• Insulin sensitivity

At the same time, they suppress genes involved in:

• Chronic inflammation

• Triglyceride production

• Fat synthesis

This helps explain why omega-3 fatty acids can improve much more than joint health—they influence metabolism throughout the body.

DHA Activates the Body's Own Antioxidant System

DHA also activates another important pathway called Nrf2, often referred to as the body's "master antioxidant switch."

Rather than acting as an antioxidant itself, DHA encourages cells to manufacture their own antioxidant enzymes, including superoxide dismutase, catalase, and glutathione-related enzymes.

Instead of delivering antioxidants, DHA teaches the body to produce them itself.

Fish Oil Changes Cell Membranes

Another remarkable effect of DHA occurs within the cell membrane.

Because DHA contains six double bonds, it increases membrane fluidity. This changes how receptors involved in immune signaling, insulin sensitivity, and neuronal communication function.

In other words, cells begin responding differently to their environment before any changes in gene expression even occur.

Why DHA Is So Important for the Brain

Nearly one-third of the fatty acids in the brain are DHA.

It is highly concentrated in:

• The cerebral cortex

• The retina

• Synapses

DHA promotes the expression of genes involved in:

• Synapse formation

• Neuronal survival

• Neuroplasticity

• Brain-derived neurotrophic factor (BDNF)

This helps explain why puppies receiving adequate DHA often demonstrate improved learning and trainability, and why DHA continues to be studied for its potential role in cognitive aging.

The Missing Half of Inflammation

Most people understand how inflammation begins.

Few understand how it ends.

We tend to think inflammation simply fades away once the injury heals.

It doesn't.

Resolution of inflammation is an active, genetically programmed biological process.

This is where resolvins and protectins enter the picture.

Resolvins: The Cleanup Crew

EPA serves as the raw material for compounds called resolvins.

Resolvins don't suppress the immune system.

Instead, they change its mission.

Imagine firefighters battling a house fire. During the emergency, everyone is focused on extinguishing the flames.

Eventually, however, someone has to tell the firefighters:

"The fire is out. Now it's time to clean up."

That's exactly what resolvins do.

They:

• Stop recruiting additional neutrophils

• Reduce inflammatory cytokines such as TNF-α, IL-1β, and IL-6

• Encourage macrophages to shift from inflammation toward tissue repair

• Increase efferocytosis, the process by which dead inflammatory cells and cellular debris are removed

Without this cleanup process, inflammation can persist long after the original injury has resolved.

Protectins: Protecting Healthy Tissue

DHA gives rise to another family of specialized pro-resolving mediators known as protectins.

Their role is exactly what their name suggests.

They help protect healthy tissue from collateral damage during inflammation.

Protectins:

• Reduce programmed cell death

• Limit scar tissue formation

• Preserve healthy cells

• Promote tissue healing

This makes them particularly important in the brain and nervous system, where unnecessary cell loss can have lasting consequences.

Why This Matters for Dogs

Many chronic diseases in dogs involve inflammation that never fully resolves.

Examples include:

• Osteoarthritis

• Periodontal disease

• Chronic enteropathy

• Allergic skin disease

• Chronic kidney disease

• Obesity-associated inflammation

Rather than simply suppressing inflammation, EPA and DHA help the body transition from injury toward healing.

Does This Actually Improve Dogs?

Mechanistic biology is fascinating, but clinical results matter.

One of the strongest studies evaluating omega-3 supplementation in dogs with naturally occurring osteoarthritis enrolled 78 client-owned dogs in a prospective, randomized, double-blind, placebo-controlled trial.

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Dogs received approximately 69 mg/kg/day of EPA and DHA for 84 days.

The results were impressive.

By 42 days, investigators documented significant improvements in joint severity and overall function.

By 84 days, dogs demonstrated significant improvements in:

• Pain

• Lameness

• Comfort

• Overall mobility

Every investigator-assessed measure of osteoarthritis improved compared with placebo.

The Biology Changed Too

Perhaps even more interesting than the clinical improvement were the changes occurring within cell membranes.

Compared with baseline:

• EPA increased 13-fold

• DHA increased 3.3-fold

• Arachidonic acid decreased by approximately 17%

• The inflammatory fatty acid ratio (ARA ÷ EPA + DHA) fell from 28.3 to 3.5, an approximately 88% reduction.

Even more compelling, dogs experiencing the greatest reduction in this inflammatory ratio also showed the greatest improvements in lameness and discomfort.

The biology and the clinical outcomes moved together.

One Final Myth

Many dog foods advertise an ideal omega-6-to-omega-3 ratio.

Unfortunately, that number can be misleading.

Many foods achieve their ratio by adding flaxseed, which supplies alpha-linolenic acid (ALA).

Dogs convert ALA into EPA and DHA very inefficiently.

Two foods may advertise identical omega-6-to-omega-3 ratios while producing dramatically different biological effects if one contains preformed EPA and DHA and the other relies primarily on ALA.

In other words, it's not just about the ratio—it's about which omega-3 fatty acids are actually present. 

The Bottom Line

Fish oil is far more than an anti-inflammatory supplement.

EPA and DHA are molecular signaling molecules that influence gene expression, cell membranes, immune cell behavior, and the active resolution of inflammation.

Rather than simply turning inflammation down, they help the body know when the battle is over—and how to heal.

That shift in perspective changes how we think about nutrition. Fish oil isn't just providing nutrients. It's helping rewrite the conversation between cells, allowing inflammation to resolve more effectively while supporting healthier joints, brains, skin, and metabolism.

As our understanding of nutritional genomics continues to grow, EPA and DHA remain among the most compelling examples of how something as simple as a dietary fatty acid can profoundly influence canine health.