The facts about protein – this is a re-print of an old article I did for my yahoogroup, in it’s heyday..but the facts are solid and we have an entry point for going deeper into exploration on the topic.The core components of a healthy and balanced home made diet are the total energy, based of course on nutrients that provide energy – protein, carbohydrate, and fat. We’ve done a lot on carbs – let’s take a look at protein.
First in a series.
This section tells you how proteins play a big role in regulating metabolism, transporting essential materials around the body and defending your dog against disease. So first – what ARE proteins?
Proteins are the essential parts of all living cells and they have many important functions. For one thing, they help build cell structures and muscle fibre. As you are probably aware, it is very important to eat enough protein so your tissues can grow and repair themselves properly. But you may not realise that proteins also play a big role in other bodily functions, such as: regulating metabolism (as enzymes and some hormones); transporting essential materials around the body; and defending the body against disease. Protein is also a source of energy in the diet and will give the same amount of energy as its equivalent weight in carbohydrate. What all this means for you as the owner of a dog, and the person who feeds him, is that you need to be aware of your dog’s protein requirements. In this section, we’ll go over the basic facts about protein, and then talk about how they apply to looking after your dog.
What are proteins? Which amino acids are essential?
Essential and non-essential amino acids for dogs
What happens to proteins in the body
The quality of protein from different sources
Why dogs need protein
When dogs need extra protein
The signs of protein deficiency How disease affects a dog’s protein needs
What are proteins? Proteins are large molecules made up of long chains of constituent units called the amino acids. Only about 20 amino acids are commonly found in proteins. But hundreds or thousands of these amino acids may be arranged in any combination to give an almost infinite variety of naturally occurring proteins, each with its own characteristic properties. Like carbohydrates and fats, proteins contain carbon, hydrogen and oxygen. Among these nutrients, the element that makes proteins unique is nitrogen, a constituent of all the amino acids. This is why nutritionists often refer to “nitrogen balance” when they assess the protein status of the body. Two of the amino acids contain sulphur, which means this element is also found in many proteins. Which amino acids are essential? Amino acids may be classified as either essential (indispensable) or non-essential (dispensable). The body cannot produce enough essential amino acids, so they must be supplied in the diet. Non-essential amino acids are equally important as components of body proteins. They can, however, be made from excesses of certain other dietary amino acids, or from other dietary sources of nitrogen. In dogs, 10 of the amino acids are essential to their diet.
Essential and non-essential amino acids for dogs
Essential Amino Acids
Notes: 1. Although classified as non-essential, cystine and tyrosine can supply about 50% of the requirement for methionine and phenylalanine, respectively
2. Methionine and cystine are the sulphur-containing amino acids.
What happens to proteins in the body
Proteins in the diet are ultimately broken down into various amino acids by the action of enzymes in the digestive tract. Shorter chains of amino acids are referred to as peptides, so the sequence goes like this: Proteins —–> long-chain peptides —–> short-chain peptides —–> amino acids This process begins in the stomach and continues in the small intestine, where the products of digestion are absorbed across the gut wall into the blood. Amino acids are then transported around the body;cells that need amino acids will remove them from the blood. Any surplus amino acids are processed, mainly in the liver, to remove nitrogen from the molecule. The nitrogen is converted to ammonia, which may be turned into new amino acids or converted to urea and excreted in the urine by the kidneys. Free ammonia is highly toxic, and urea is one of the few safe forms in which nitrogen can be eliminated from the body. The remainder of the amino acid molecule is used as a source of energy, or stored as fat.
The quality of proteins from different sources
When you’re choosing food for your dog, you need to consider (among many factors) the quality of the protein it contains. Quality in this case starts with digestibility and amino acid composition. The amino acid profile of a food reflects which of the 20 amino acids it contains; the highest quality proteins contain the highest levels and best balance of the essential amino acids. These highest quality proteins are found in the food young animals eat: eggs and milk. Next come animal tissues such as meat and fish, and then vegetable and cereal proteins. Vegetable and cereal proteins generally have much lower levels of the essential amino acids, and need to be mixed with other protein sources to provide a diet that includes adequate overall protein quality. Still, this is a generalisation, and there are some vegetable protein sources, such as soya protein concentrate, that have a high digestibility and a reasonably good amino acid profile.(not that I’m recommending soy, just a bit of information). How digestible a protein is shows how much of the protein an animal eats is actually absorbed across the intestinal wall, into the body and then available for a variety of uses. For dogs, the digestibility of protein varies from around 70% for some vegetable proteins, to between 90% and 95% for egg and milk proteins. In general, dogs can digest proteins of animal origin more efficiently than most vegetable proteins. But there can be a considerable overlap, depending on the protein source and the way the food is prepared. This doesn’t mean dogs should be fed entirely on milk and eggs! In fact, some dogs may not tolerate dairy products very well because they may not be able to digest large amounts of lactose, the sugar in milk. The key factor here is proper mixing of different protein sources to provide a well-balanced, digestible diet- if possible. If your dog doesn’t tolerate mixed proteins, you can try feeding them separately, at different meals – or maybe do with a singe source and supplement accordingly.
Why dogs need protein
Animals need protein in their diet to satisfy two needs: A).. to provide the essential amino acids that their own tissues can’t make, and B).. to provide nitrogen for making non-essential amino acids and other nitrogen-containing compounds. Some protein is lost from the body every day, even in adult dogs. All dogs have a continuous need for dietary protein to replace the protein they lose during the natural turnover of skin, nails, hair and other body tissues, and in secretions; some of the products of protein breakdown are also excreted in the urine. Also, about 1% of body protein is broken down and re-synthesized every day. But this can’t happen if the body isn’t taking in enough protein, because the supply of some essential amino acids will be limited. And if a dog isn’t taking in enough overall energy, protein synthesis may be compromised, because some released amino acids will be used as an energy source. This will trigger some signs of protein deficiency.It’s important to meet, but not significantly exceed, daily requirements.
When dogs need extra protein
Dogs need extra protein when they’re growing, pregnant, or lactating, and when their bodies need to repair damaged tissue. During these critical times, protein quality and digestibility are most important. Growing puppies need greater levels of protein in their diet so new tissues can grow and for normal maintenance. But the minimum protein requirements vary widely according to breed differences, environmental factors, and variations in the dietary source of protein. People often mistakenly believe that large amounts of extra protein will help a growing puppy develop condition and muscle. Unfortunately, this isn’t the case, since any surplus protein a dog consumes is simply converted to energy. Excessive energy intake in growing dogs can lead to problems such as fat deposits and obesity in small breeds and skeletal developmental abnormalities in large breeds.Growth diets should always be formulated by someone with both training and experience in these all-important calculations.
The signs of protein deficiency
Protein deficiency, resulting from either insufficient dietary protein or from a shortage of particular essential amino acids, can lead to generalised weight loss in adult dogs and poor growth in puppies, and to muscle wastage. Other signs include a depressed appetite, rough and dull hair coat, increased susceptibility to disease and, in some cases, edema (retention of fluid).
How disease affects a dog’s protein needs
Dogs that are stressed, through injury or disease, often have greater than normal protein requirements. Unless your vet tells you otherwise, a diet for your dog under these conditions should contain enough protein to support normal growth. But there are certain medical conditions where some restriction of dietary protein may be beneficial. In dogs with developed kidney failure, the kidneys become less efficient in eliminating the toxic products of protein breakdown. By restricting the protein intake, and by using only high-quality proteins, the breakdown of non-essential protein is limited, and toxic waste production is produced. Many of the clinical signs of kidney failure can be improved by feeding your dog a diet with a reduced level of protein, but high-quality protein. You may individually adjust the level of protein according to the severity of your dog’s condition. Furthermore, protein restriction may not be necessary in early cases of kidney failure(although we do start mineral restriction at the first signs). . Similarly, dogs with liver disease may have difficulty processing the nitrogen waste products of protein breakdown. They may benefit from a moderate restriction of their dietary protein. The liver, though, has a great capacity to regenerate and the protein content of the diet should be high enough to support growth of the organ during the critical period of repair. So you need to balance carefully the level of protein in your dog’s diet according to his needs. Changing the source, but not the level, of dietary protein may also be a good idea in managing some cases of food allergy in dogs. Although this condition isn’t common, some animals do develop an allergic response to certain proteins or other ingredients in their diet. In dogs, the proteins most commonly implicated in food allergy are cow’s milk, beef and chicken–alone or in combination. The aim in managing this condition is to find out what the offending ingredient is, and remove it, in all its forms, from the diet. You then need to feed a balanced diet, using one (or a very limited number of) alternative source(s) of protein.
ADDITION TO THE ORIGINAL ARTICLE
on January 15, 2009 A member asks: “I can understand why no one wants to say what the upper limit of Protein is but I’m surprised that no one knows what the lower limit should be. Why is there such a mystery about how much Protein is enough?”
There is absolutely no mystery about this, the 2006 NRC Guidelines state it clearly:
Minimal requirement = 2.62 grams per kilogram BW ( to the power 0.75)
Recommended Allowance = 3.28 grams per kilogram (to the power 0.75)
Safe Upper Limit = NONE
Protein requirements are also influenced by various factors such as the dog’s overall condition, the digestibility of the food source, activity level and others. In general, when I formulate a diet for a healthy dog, I use 2 – 3 times the recommended allowance. So let’s take a look at an example. My 75 lb dog. First, take the weight in kilograms – so 34.01 kgs. Next, we take this number to the power of 0.75 – easily done on one’s computer calculator: we get the number 14.08. This is the number that will represent my dog in all calculations from here on in, his metabolic weight. To now find his “requirement” – let’s say, his RA or recommended allowance, all we need to do is multiply his number – 14.08 – by the RA – 3.28.
Here’s what we get: 46.182. That’s the recommended gram weight of total protein for the day. If I were to put this strictly into practice, I would end up with a percentage of total protein probably around 15% I am guessing. So let’s have a peek and see. I’ve formulated a diet for Daniel that contains only 46 grams of protein per day. I will also use the RA for total fat, which in this case would be 27 grams. His caloric needs are 1840 per day, so if I devise a very simple diet of brown rice, coconut oil and turkey, and stick strictly to the RA for fat and protein,I would get percentages like this:
Distribution of calories:
Protein: 11.3 %
Fat: 15.6 %
Carbohydrate: 73 %
I would also be feeding this:
1. Turkey, Dark Meat w/skin, boneless, roasted, diced 0.33 of: 1 cup, diced (46.2g)
2. Grain, Rice, Brown, ckd 7 of: 1 cup, cooked, hot (1365.0g)
3. Oil, Coconut 1 of: 1 tbsp (13.5g)
That’s right – SEVEN cups of brown rice, and a third of a cup of turkey. This diet technically meets the RA for protein and fat. Of course it doesn’t take into consideration fatty or amino acid levels or vitamins and minerals, this is an exercise to show how there is so much confusion between percentages and actual gram content. I often develop diets for dogs with liver issues where the protein percentage is in the midteens but the gram content is actually over the RA. Vets will want a higher level based on percentage but after we speak they understood that percentages are not the whole story. They tell us how much of a given nutrient the diet contains – RELATIVE to other energy nutrients. In actual practise, I use much – MUCH higher levels of protein and fat in my own dog’s diet as well as professional cases. It’s not in any way optimal to feed a 75 pound dog 1/3 of a cup of meat and 7 cups of rice per day. When we look at the recipe above we also will see that no less than 34 of the 46 grams of total protein come from the rice. So if we were to use more sweet potato than rice we could actually inch up the turkey a bit…. but the poor dog who has to eat so much carb and so little protein! Let’s not forget that from mouth to tail, dogs are carnivores, and derive most quality nutrients from animal sources. I have long defended the use of fiber in the canine diet, because I am not so much interested in what wolves do or don’t eat – on a practical level, at any rate – but in what type of diet is absolutely optimal for the individual dog I’m working with. This always means some fiber, although the type and amount will vary. But all that said, animal products – protein and fats – should form the mainstay of a healthy dog’s diet. This menu I used above as an example is lower than what I’d use for dogs with liver disease,by far – yet it meets the NRC Guidelines for requirements.
To start working out the amount of protein to use (we’ll get to sources later) find your dog’s protein RA first, then in a home made diet, go 2-3 times above that in grams. You have a huge range of fat to play with, and what works best will often be a matter of some trial and error (and sources, many dogs can take the same amount of fat if it’s fish based and higher in Omega3 than they can from beef or lamb, or who actually tolerate coconut oil better than animal-fats; it’s really very individual with fat, but that’s another topic). I know this was lengthy and detailed and may be hard to follow if you aren’t used to thinking in numbers. And it is very superficial nutrition - foundational might be a better word -but extremely important nonetheless. The calories your dog eats, and how those calories are divided between fat, protein and carbohydrate are foundational to how you develop a home made diet, that’s the first step. You will eventually need to think about things like fatty and amino acids, food sources and anti nutrients, biological value – it does get complex. But in terms of protein, there is no safe upper limit – on paper at least. This doesn’t mean that feeding a huge amount of animal protein is advisable; in some cases it can even be dangerous. But there is no need to fear a healthy level of varied animal protein in a normal dog’s diet. In fact, it’s one critical component of an optimal, personalized, health-supportive diet.