Food for thought

I don't understand protein levels in pet foods - if you look at dry food and wet food it just looks completely different. I'm guessing dry food has the moisture taken out so the protein level looks much higher. What formula do you need to use to compare like with like? And are all wet foods the same - what about whole foods like tinned fish? Aren't they different to ones with added carbs?
What I don't get is even if I look at a tin of something like sardines for human use, the protein percentage is really low - like 10%. There's nothing else in the tin but fish so far as I can see - so what's the other 90%
But then I got to thinking hold on isn't that normal? Aren't we 90% water? Why should we expect 'real' food to have any less moisture than we have?
Is there someone who could explain it to me what we should look for in a food which presents bits of an animal we can still recognise as opposed to ones with ash and feathers and all sorts of other things?
I'd like to feed my dogs and cats a protein source that is as unmessed with as possible. If so how much protein should I be aiming for ideally and what other ingredients should I add to make the mix perfect?


You’re quite right, dried foods will always ‘seem’ to be higher in protein because they are low in moisture. A wet food may be 10% protein but 75% water, so the non water ingredients are relatively high in protein (in other words after you take the water out, 40% of what is left is protein). On the other hand a dry food that is 25% protein and which has virtually no water in it is still 25% protein in comparison.
However, it’s much more complicated than that because how much protein the dog takes in depends on how much volume of food is eaten and then to confuse matters more, not all of the protein is actually digested equally well. On the label of a bag or can of pet food the ingredients are listed in order of weight. If the first ingredient is chicken or lamb you can take it as being a good quality protein source. ‘Chicken by-product’ or other meat by-products are not as good; meat and bone meal are poorer yet. If grains are listed, they are not as digestible a source of protein and contribute heavily toward the carbohydrate load. Even after digestion there are more differences. Different proteins have different nutritional values. The ability of a protein to be used by the body and its amount of usable amino acids is known as the biological value. Egg has the highest biological value and sets the standard for which other proteins are judged. Egg has a biological value of 100. Fish and milk are close behind with a value of 92. Beef is around 78 and soybean meal is 67. Meat and bone meal and wheat are around 50 and corn is 45. Things like hair and feathers would be very high in protein but would be down at the bottom of the list for biological value.
So all in all go for fresh real food where possible so you know its good quality; if you are giving processed food look for meat rather than meat by products and meat meal; and above all avoid like the plague foods with high carbohydrate content. In principle, the more (high quality) protein the better, some fat is fine, and the fewer carbohydrates the better.
A final point about ash. Ash is not cinders from the fireplace and cigarette ends added to bulk out the food. It is simply the inorganic matter (minerals, vitamins, trace elements) in the diet. Ash content is calculated by incinerating the food; the ash is what’s left (which explains why it is called ash!).A diet containing bones would be, naturally, high in ash, but very healthy all the same.
Richard Allport, alternative vet

Richard Allport says that the diet should be high in protein, some fat is OK and carbohydrate should be avoided like the plague. He mustn’t be allowed to get away with that. What is the merit in a high protein diet? How can you feed high protein without high fat too? They go together in most meat sources. There may be cases where a high protein and low carbohydrate diet is important but there cant be many. In my experience excellent health benefits are achieved when the diet is high in complex carbohydrate (whole grains), and low in fat and protein.
The correct way to compare wet and dry foods is to compare by dry matter (DM) content. Look first at the declared moisture content.
Let’s take a wet food with 80% moisture and 10 % protein.
Subtract 80 from 100 to get the dry matter content which is 20%.
Think of this as 20 gr of DM in 100 gr food.
10 % protein means 10 gr in 100 gr food
So the food has 10 gr protein in 20 gr DM i.e. 50% protein on a DM basis.
With a dry food
Say 10% moisture and 20% protein
This means on a DM basis 20 gr protein in 90 gr food
This equates to 22.2% protein on a DM basis (20/90 x100)
So the dry food which seems to have twice as much protein actually has a lower protein content on a DM basis.
As Richard Allport says, protein levels don't mean much unless you also consider digestibility.
John Burns BVMS MRCVS, Burns Pet Nutrition