Sodium : potassium ratio (Na:K)

Sodium and potassium are a pair of electrolytes that together regulate blood pressure, fluid volume, nerve and muscle function — sodium is the main cation of the extracellular fluid, potassium of the intracellular [1]. In a BARF diet the problem is almost never potassium itself (muscle meat is full of it), but the shifted Na:K ratio — usually too low, because store-bought meat is bled out and poor in sodium, while there is plenty of potassium in meat and hearts.

Why the ratio, not the amount alone

Raw muscle meat and offal are naturally rich in potassium and at the same time poor in sodium, because blood — the main carrier of sodium in the carcass — is mostly removed at slaughter [1]. The more heart in the diet, the more the Na:K ratio drops, because heart is especially rich in potassium and poor in sodium [1]. That's why sodium deficiency in BARF is more common than it seems, and it almost always concerns low sodium with correct potassium — not the other way around.

What it means in practice

• Too low Na:K (too little sodium) — the most common scenario. Symptoms can be subtle: weakness, accelerated pulse, licking strange surfaces, in the cat lowered appetite and lethargy [1]. Solution: add ordinary non-iodized salt (1 g of salt ≈ 400 mg of sodium — use a conversion factor instead of "a pinch"). Natural sources are blood and whole prey. Iodized salt disrupts the control of iodine supply, to whose excess cats are particularly sensitive. More in the article Sodium.
• Too high Na:K (too much sodium) — unlikely in a precisely calculated diet; it happens with "eyeball" salting or salty human products. A healthy dog or cat with access to water copes well with a moderate excess, and the high moisture of a raw diet (65–75%) gives the kidneys a buffer [1]. More about the second component in the article Potassium.
• When salting with table salt (NaCl), you simultaneously supplement chlorine — check both parameters. Also don't pour out the juice from thawing meat, because potassium is dissolved in it and you really lose it.

Note: with kidney disease (CKD), heart, adrenal disease, or treatment with diuretics, set the sodium dose with a veterinarian — diuretics and ACE inhibitors strongly change the electrolyte balance [2].

Sources

1. National Research Council (2006). Nutrient Requirements of Dogs and Cats. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
2. MSD (Merck) Veterinary Manual. Overview of Disorders of Potassium Metabolism in Animals. https://www.msdvetmanual.com/metabolic-disorders/disorders-of-potassium-metabolism/overview-of-disorders-of-potassium-metabolism-in-animals
3. FEDIAF. Nutritional Guidelines for Complete and Complementary Pet Food for Cats and Dogs. https://europeanpetfood.org/self-regulation/nutritional-guidelines/