Online Extra! More from Salt: is there really anything wrong with it?

Exclusively on the web - take a look at Dr. Aldrich's entire Ingredient Issues column from the January 2008 issue of Petfood Industry

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Salt: is there really anything wrong with it?

For years, salt had been one of those ingredients in petfood that was so innocuous it had become almost invisible. Recently, though, consumers have been expressing concerns about it. This can be best demonstrated with a visit to almost any petfood company's website, where you'll find Q & A dialogue about why salt is added to the food. This new attention to salt would indicate it has become one of those ingredients with an issue.

To generalize, the pet-owning public perceives salt in petfood is unhealthy and is being added as a seasoning. The issue likely stems from pet owners assuming their dogs and cats have the same dietary health problems with sodium and hypertension that people have. For example, one supposed pet nutrition website states that salt is "used to cover up rancid meat and fat, [it] can cause kidney and heart disease [and] hypertension."

This is just plain wrong. Salt will not fix rancid ingredients, and its ingestion is not the root cause for these organ failures. Short of renal or heart failure, hypertension is not a big issue for dogs or cats. So … is there really anything wrong with salt?

From lethal to harmonious

Salt (sodium chloride) is the combination of the explosive element sodium and the toxic gas chlorine. These two otherwise lethal elements come together harmoniously to form a benign rock found in nature as halite. In its pure form, it consists of 60.67% chloride and 39.34% sodium.

Commercially, salt is derived from three avenues: mining (rock salt), evaporation from underground brine deposits or solar evaporation of sea water (sea salt). Accounting for impurities and the addition of flow agents, most salt is traded at 95-98% purity.

Although there are salts from around the world that carry a color due to contamination with small amounts of minerals like cobalt or zinc, the salt commonly used in petfood is translucent to opaque white. The other form of salt used in petfood is iodized salt; the addition of iodine is a means to prevent goiter. In past centuries, salt was a precious ingredient often used as currency, but today salt is an inexpensive way to get sodium and chloride, and even iodine, into the diet.

Leap in logic

Salt has traditionally been used as a preservative for fish, meat and some vegetables. Now, it is used every day as a seasoning on human foods. Just a dash will help add flavor to most any dish, and a thick coating is almost a necessity for snacks like potato chips, nuts and pretzels.

This free use of salt as a seasoning is a fairly recent application in people's diets and has probably caused the greatest opportunity for misunderstanding of its use in petfood. The consumer must be making the leap in logic that the mere presence of salt on the ingredient panel means the pet's food is being flavored with excessive amounts of salt. The flaw in this theory is that most petfoods do not rely on salt as a seasoning. If you have ever tasted petfood, you know one thing for sure: It is bland. For our palate, petfood could do with a bit of salt seasoning. However, that is the point; salt is primarily being used in petfood to a level necessary to meet the nutrient requirements.

Both sodium and chloride are considered essential minerals in dog and cat diets. Deficiencies in sodium and chloride result in problems with nervous signal transmission, low blood pressure, restlessness, increased heart rate and pasty or thick mucus. The requirements (on a diet dry matter basis) range between 0.06-0.30% for sodium and 0.10-0.45% for chloride depending on species and lifestage.

How is this being met? Well, if you took a quick survey of nutritionists and asked them how much salt they customarily add to their formulas, the response would overwhelmingly be 0.25-0.50%. This amount of salt satisfies one-half to the entire requirement for these two minerals (0.25 to 0.50% salt in the formula would contribute 0.09-0.15% sodium and 0.20-0.30% chloride).

The other factor that makes the addition of this minimal amount possible is that digestibility and absorption of sodium and chloride from salt are nearly 100%. Interestingly, salt will improve palatability with each increment up to 0.50% of the formula; but beyond this point, palatability does not seem to improve. Thus, there is no real incentive to "season" beyond the minimum requirements.

Functional ingredient?

There are a few examples in which salt falls into the functional rather than the nutritional ingredient category. Salt has been used to stimulate water intake-most notably in feline diets to promote more dilute urine. In addition, elevated levels of salt are found in some treats and semi-moist foods where it is used to help control water activity as part of the preservative system.

But at what level is this functional salt a problem? In the dog and cat, adverse effects have been noted for excessive consumption of sodium and chloride that would translate into 2.5% of the diet as salt. However, this level would lead to food refusals and regurgitation before the ingested salt could become harmful. Conditions of salt toxicity can occur but typically result from extreme circumstances in which fresh water and wholesome food are unavailable.

While salt seems to have fallen into a bit of controversy recently due to its perception as unhealthy or as a petfood seasoning, the nutrition and integrity of the ingredient has not changed or eroded. Salt remains the most cost-effective and prudent source of supplemental sodium and chloride in the diet and should continue to hold its place on ingredient panels for the foreseeable future. Rather than play on the confusion, the petfood industry should strive to educate consumers regarding the essentiality of sodium and chloride and that salt is a safe and cost effective means for their delivery. Sodium and chloride are considered essential minerals in dog and cat diets.

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