Fish is an integral part of the Real Ancestral 6X Diet™ (Real Ancestral Diet), a species-appropriate diet providing essential nutrients to keep your dog happy and healthy. The benefits of adding fish to your dog’s diet must also include learning about thiaminase, an enzyme in fish. that can interfere with another essential nutrient in your dog’s meals.

Thiamine, commonly known as vitamin B1, is a water-soluble organic compound cofactor in carbohydrate catabolism. Although mammals can synthesize this compound in their gut, most of it is consumed by the diet. 

If dogs have a minor deficiency in thiamine, they will have a more difficult time digesting carbohydrates. This is particularly hard on dogs who eat kibble due to its carb content. A minor deficiency may lead to weakness, but a severe deficiency could lead to neurological problems.

As a water-soluble B vitamin, thiamine plays a critical role in energy metabolism and the proper functioning of the nervous system. Vital functions of thiamine include:

Energy Production: Thiamine is a crucial component of various enzymes involved in carbohydrate metabolism. It helps convert carbohydrates from the diet into glucose, which is then used by cells as a primary source of energy. Without adequate thiamine, dogs may struggle to utilize the energy from their food efficiently.

Nervous System Function: Thiamine is essential for maintaining nerve cells' health and proper functioning. It transmits nerve impulses and helps support the nervous system's overall health. Dogs rely on a healthy nervous system for proper muscle function, coordination, and sensory perception.

Enzyme Activation: Thiamine is a cofactor for several enzymes that participate in various biochemical reactions in the body. Enzymes with thiamine as a cofactor are involved in the breakdown of nutrients, including carbohydrates and amino acids.

Brain Health: The brain requires significant energy to function correctly. Thiamine's role in energy metabolism is vital for maintaining optimal brain health and cognitive function.

Stress Management: Thiamine is involved in the body's response to stress. During periods of stress, such as illness or physical exertion, the body's thiamine requirements may increase.

Cell Growth and Function: Thiamine is necessary for proper cell growth, division, and overall cellular function. Adequate thiamine levels are essential for maintaining healthy tissues and organs.

Metabolic Processes: Thiamine is involved in various metabolic reactions, including those related to the metabolism of fats and certain amino acids.

Thiamine is essential to your dog’s overall health and well-being. Knowing that an enzyme in fish can denature thiamine may scare you from feeding fish—however, the benefits of fish outweigh the risks. Your dog can have both nutrients without worry. 

The primary sources of thiamine for a fresh food diet are muscle meat, organs, and eggs. 

Lean meats contain some thiamine, such as chicken, beef, pork, and turkey. While lean meats are not as high in thiamine as organ meats, they can contribute to your dog's overall intake. Muscle meat comprises 63-65% of your dog’s bowl with the Real Ancestral 6X Diet™.

Many organ meats are excellent sources of thiamine. Heart, liver, and kidney are particularly rich in thiamine and can be included in your dog's raw diet. The Real Ancestral 6X Diet™ calls for 5% liver and 5% other secreting organ meat.

Eggs contain a small amount of thiamine and can benefit your dog's diet. Read about The Benefits of Pasture-Raised Eggs for your dog.

For dogs that will eat vegetables, you can give them spinach, asparagus, brussel sprouts, cabbage, bell peppers, and carrots for low thiamine levels. Vegetables must be processed, steamed, pureed, fermented, or minced to be digested by your dog.

Strawberries, blackberries, raspberries, pineapple, and kiwi contain low thiamine levels.

When feeding your dog a fresh diet, the primary sources of thiamine will be from the muscle meat and organs. Providing high-quality meat from organically pasture-raised animals will yield the highest thiamine levels.

Thiaminase is an enzyme that can break down or degrade thiamine. An enzyme is a protein molecule that acts as a biological catalyst, facilitating and speeding up chemical reactions in living organisms. Enzymes are critical in various biochemical processes within cells and are essential for properly functioning biological systems.

Thiaminase is found mainly in some raw fish and certain plants. When ingested, thiaminase can lead to thiamine degradation, reducing its availability for your dog’s body to use. This can lead to thiamine deficiency, which can have serious health consequences. Fish that are known to contain thiaminase include:

Chub mackerel / Pacific mackerel (Scomber japonicus)

Seafood that contains thiaminase includes:

As you can see on the list, thiaminase is not found within a particular family of fish but rather in a specific species. Not all fish contain thiaminase in their flesh. And ironically, many fish also contain thiamine!

Most enzymes, including thiaminase, end with ‘ase’ at the end. An enzyme is responsible for increasing the efficiency of biological reactions and works by binding to specific molecules. Thiaminase binds to thiamine and renders it inactive.

Many fish species contain thiaminase and, as a result, have been identified as potential sources of excess vitamin B insufficiency in dogs if included in their diet. However, when examining how the interaction occurs, it can be seen that your dog can enjoy the benefits of fish without becoming thiamine deficient. 

One key factor is the percentage of muscle meat versus the percentage of fish in your dog's bowl. Muscle meat in an ancestral diet comprises at least 63-65% of the bowl, whereas fish comprise only 10%. So even if a small amount of thiaminase activity happens when you combine fish and muscle meat in your dog’s bowl, the level of enzymatic breakdown of thiamine is minimal. 

Many dog parents like to food prep weekly or even less often and then freeze the meals until needed. There are options when feeding your dog an ancestral diet that contains fish; 

Choose fish that are known to be thiaminase-free

Freeze your prepped meals without the fish component, and add it when you feed your dog. 

Feed the fish in a separate container or at a different time.

Add the fish to the meal, knowing that the enzymatic process is reduced with freezing and that there is a minimal risk that some of the thiamine in the muscle may be denatured. 

Not all fish have significant levels of thiaminase, and some fish species have very low or negligible levels. This variation can depend on the fish's diet, habitat, and genetic factors. Additionally, thiaminase activity can be reduced or deactivated through cooking, heat processing, freezing, air drying, or freeze drying. Unfortunately, there are no practical ways to measure thiaminase levels.

A thiamine deficiency can lead to a condition called beriberi, characterized by neurological and cardiovascular abnormalities. Thiamine deficiency is relatively rare in dogs but can occur if they are fed diets lacking essential nutrients or diets with thiaminase-containing foods (foods that break down thiamine). Thiamine deficiency can have serious health consequences, including neurological issues and metabolic disturbances. 

Clinical signs of a thiamine deficiency occur within several of the body’s systems, including the nervous, gastrointestinal, and cardiovascular systems. Eye abnormalities and changes in behavior can also occur.

Neurological signs include a wobbly or unsteady gait, weakness or lack of coordination, tremors or seizures, head tilt, loss of balance, paralysis of the hind limbs, difficulty in controlling movements, rigidity in the limbs, and coma.

Indications of gastrointestinal upset you may witness in your dog are decreased appetite, vomiting, diarrhea, and abdominal pain.

Cardiovascular signs include rapid heart rate (tachycardia) and a weak, thready pulse. Uncontrolled panting and restlessness often accompany these signs of heart abnormalities. 

Eye abnormalities can cause some clinical signs that appear to be neurological. Your dog may experience pupillary dilation, acute blindness, nystagmus (involuntary eye movement), or other abnormal eye movements.

Thiamine plays a crucial role in your dog’s behavior due to its influence on the gut microbiome. With a thiamine deficiency, you may notice several behavioral changes like depression, lethargy, and irritability.

Thiamine deficiency is relatively rare in dogs. However, a thiamine deficiency can progress rapidly and be life-threatening if not treated promptly. A veterinarian will perform a thorough physical examination, review the dog's diet history, and recommend blood tests to diagnose the deficiency.

The inherent risk of an all-fish diet is appropriately recognized in a research study that explored the severe thiamine deficits encountered by a team of 12 sled dogs. After being fed fresh frozen carp and suckers for six months before clinical signs appeared, the dogs involved in the study developed a severe thiamine deficiency. 

The dogs' necropsies (examination of the body after death) demonstrated decreased thiamine levels due to the all-fish diet, which was associated with neurological manifestations and, eventually, death.

This case study does not suggest feeding these thiaminase-rich fish types is an issue. Instead, it revealed the problem of excessive raw fish consumption without nutritional diversity. Moderation and variety are critical for all diets. Any food type in excess can result in nutrition-related ailments.

Thiaminase activity can be reduced by freezing, cooking, or heat-processing foods. However, the extent to which thiaminase is inactivated depends on various factors, including the temperature and duration of freezing.

Thiaminase and Fish

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