All about protein

A quick Google search can bring you up all sorts of information about pet food and protein. I find a lot of the misinformation around pet food tends to center around protein – how much your pet needs, where it should be on an ingredient list, more meat means more protein…the list goes on. I could talk forever about these questions and assumptions around protein, but I’ve tried my best to make a concise summary of the common questions I get asked in this post.

So, today’s post is all about the questions around protein, and the truth about what your pet actually needs.

Photo by Nataliya Vaitkevich on Pexels.com

What is protein?

Protein is an essential nutrient for cats and dogs and has several functions in the body; it is a structural component of body tissues and organs such as cartilage, muscle fibres, skin and hair while also being critical to components of blood, cells in the immune system and hormones in the body. Proteins are large, complex molecules that are built by thousands of individual units, called amino acids, joined together. The order in which amino acids are connected code for a specific protein within the body, which perform different functions. There are around 20 different types of amino acids that can be strung together to form a huge number of different proteins. While animals do not have a requirement for protein, they do have an amino acid requirement which can be provided in the form of protein – either animal or plant, or a combination of the two. Each protein source will have its own amino acid profile, but few contain all the necessary amino acids – this is why you’ll often see a combination of protein sources in a diet. Essential amino acids must be supplied in the diet as pets cannot synthesise them within the body, these are:

The structure of proteins – amino acids bond to form a polypeptide chain, which can then bind with other chains and fold on itself to form a protein
  • Arginine
  • Histidine
  • Isoleucine
  • Leucine
  • Lysine
  • Methionine
  • Phenylalanine
  • Tryptophan
  • Threonine
  • Valine
  • Taurine*

*Taurine is essential only for cats, dogs can make their own taurine from methionine and cysteine.

How much is enough? Should I be feeding a high protein diet?

I get asked about protein levels more than any other macronutrient in the diet. Human food trends have lead us to believe that more is better and that all protein goes to your muscles. This is not the case. As we looked at above, protein does not just go straight to your muscles – it actually is used by a number of functions in the body, and depending on the type of protein and its amino acid make up, it will serve different functions. It is also important to consider digestibility of protein when looking at protein levels – digestibility is a measure of how easily digested and utilized by the body that the nutrient is, because if you cannot digest and use the protein (or any other nutrient), it doesn’t matter how much is in there because you will simply excrete it as waste. It’s also important to remember the body can only use the amount that it can both digest and absorb, anything in excess of this will be excreted, or it may be stored as excess calories. The excretion process takes place in the kidneys, which in senior pets can place undue pressure on them and create buildup of urea and harmful by-products of protein digestion.

So how much protein does my pet need? This depends on a few factors; age or life stage (e.g. growing animal or an adult), physiological state (e.g. pregnancy, lactation or a specific health condition) and how active they are. Puppies and kittens have approximately double the protein requirements that adult animals do. Dogs need a minimum of 18% protein on a dry matter basis and cats need a minimum of 26% protein on a dry matter basis. Beyond these requirements being met, additional protein has no extra benefit.

Why does my diet have less protein than the requirements?

When reading a pet food label, its common practice for pet owners to see the Guaranteed Analysis where the Crude Protein % is listed and take this to be a true representation of the protein level in the diet. As I mentioned above, we should be looking at protein (or any nutrient) on a dry matter basis – this is a true measure of the nutrient once all the water is removed. Crude protein doesn’t refer to the exact amount of protein in the diet, or even the quality of that protein – it is an estimated value. Crude protein is a measure of the nitrogen content of the food, which is a way to estimate the amount of protein in the diet; as nitrogen makes up part of amino acids, you can indirectly calculate the amount of protein in a diet using the equation where nitrogen percentage in the food is multiplied by 6.25. Generally speaking, crude protein can be 2% higher than the reported value and this is also why the percentage on the label may appear less than the AAFCO minimums. Now, the issue with this is that crude protein, unlike dry matter basis, doesn’t give us a true value with the water removed so when we compare diets like wet and dry, we need to convert the values to a dry matter basis to actually make a true comparison.

Table 5-13: Total crude protein and digestibility of plant and animal protein sources in dog foods, Chapter 5 – Macronutrients, Small Animal Clinical Nutrition.

Shouldn’t my diet have meat protein as the first ingredient?

Ingredients are listed by pre-processing weight which means we need to consider the format in which the ingredient is added into the diet; ingredients that are very rich in moisture such as ‘fresh chicken’ will be heavier by water weight than an ingredient that was added into the formula once the water was removed such as ‘chicken by-product meal’. Again, when we think about protein on a dry matter basis, we know that a protein source with the water removed will be higher in protein than one that has a higher proportion of water in it, despite the fact that it weighs less. So, an ingredient that has had the water removed, that appears lower on an ingredient list, doesn’t mean it has less protein. As for it being a meat protein source, as we talked about before, the amino acid profile of the ingredient is most important as we need to meet the patient’s requirement for amino acids; no one meat source contains every essential amino acid, so adding a plant protein source can help ensure the entire profile is present in the diet. If the plant protein source is higher on the ingredient listing, this doesn’t necessarily mean there is more plant material in the diet (it may contain more water, or the meat source is dried and weighs less) or that the diet is lower in quality – again the ingredient list isn’t an indicator of quality. The combination of protein sources also ensures that all amino acids are digestible and bioavailable to the pet.

As I always say, I recommend looking for diets that follow the WSAVA guidelines and are based on scientific principles, not marketing. When thinking about protein, its so important to consider the science as to why diets are formulated in the way that they are, and the ingredients are chosen for a reason. Protein is one of the most weaponized nutrients when it comes to marketing – I recommend learning how to recognise marketing, buzzwords, and ingredient myths which I’ve covered in previous blogs.

Do you consider the protein content of your pet’s diet when choosing it? Did this blog help clear up some myths around protein? Let me know in the comments below!


References

Small Animal Clinical Nutrition 5th ed. Chapter 5 – Macronutrients

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