Overnutrition: Phosphorous

More and more pet foods are formulated for all life stages, including growth. While this creates significantly greater options for puppies and makes it easier for manufacturers. This means that adult dogs receive higher levels of many nutrients.  

While there are few true known nutritional maximums, providing several times the recommended levels of many nutrients probably isn’t ideal. While it might not be harmful in the short term, the long-term effects, i.e., for several years, haven’t really been evaluated. 

Phosphorous 

While cats get kidney disease at a much higher rate, the disease is becoming more prevalent in dogs. One of the biggest issues with kidney disease is that it doesn’t become noticeable until around 70% of the kidney is already damaged.

Minimum Level of Phosphorus per 1000Kcals

Having reviewed the nutrient profile of many foods, most foods contain significantly higher levels of phosphorus, with some manufacturers containing several times the minimum.

While it’s not known yet whether the long-term supply of, say, 150%, 200%, 350% of a dog or cat’s recommended amount of phosphorous is a contributing factor to the increase in kidney disease, it probably doesn’t help over the course of a dog or cat’s lifetime as there really haven’t been any chronic toxicity studies.

There is a complicating factor in that some inorganic sources of phosphorus (similar to copper) are significantly more biologically available than organic sources, ie, bone or bone meal. There is also variability between different inorganic sources as well. So, the amount of phosphorous listed on the bag doesn’t tell you the whole story, as manufacturers don’t have to differentiate between the different sources of phosphorous.

I.e., two foods, one where most of the phosphorous comes from poultry meal, and another from dicalcium Phosphate. Poultry meal has significantly lower bioavailability than dicalcium phosphate. While beef bone meal has relatively similar bioavailability to dicalcium phosphate. 

This is a relatively common problem with setting nutritional limits. For example, pro-vitamin A from spinach probably isn’t going to cause an issue when given in excess, while vitamin A from beef or chicken liver will cause issues.

This, along with the amount and ratio of specific nutrients, complicates any epidemiological studies into the role nutrition plays in different health conditions, whether it is too much protein, phosphorus, sodium, copper, or, in the case of vitamin D, possibly not enough.

Vitamin D2: Plant-based diet and Raw Dog Foods that rely on mushrooms to meet Vitamin D Requirements

Historically, dog foods have largely relied on vitamin D3. There is a significant need for research into using Vitamin D2 to meet the vitamin D requirement. Vitamin D2 and Vitamin D3 do produce different metabolites, with the biological significance currently unknown. Mushrooms should not be given raw, they need to be either gently cooked or steamed to improve digestibility. It is unclear if the raw dog food companies including mushrooms in their diets are 

Cats are much more prone to developing kidney disease. This is partly due to the fact that cats often drink far less water than dogs, which results in more concentrated urine. That being said, it is negligent not to consider the role of including 150%, 200%, etc., the amount of phosphorous or even protein for that matter, over the course of their life.

What you can do in the meantime 

If you have an older dog, look for a diet that is closer to the minimum level of phosphorus, especially if you have a highly active dog. If the information is not listed, look for food lower in ash. Look on the ingredient list to see whether most of the phosphorous comes from organic sources ie chicken bone or chicken meal vs inorganic sources ie tricalcium phosphate. In dry foods where chicken, beef, pork, etc, meal is included, if the ash content (Mineral Content) is higher than 7%, it can be a sign that the company is using lower quality (High Ash)meat meals. There are dog food companies using the feeding trial loophole to advertise their food as complete and balanced despite being over the maximum for certain nutrients.