I have an "against the grain" opinion on this approach to nutrition and health. See if you don't agree...
First of all I object to the underlying premise of % based nutrition, namely that science has reached a stage of knowledge where they know precisely how much of which nutrients creatures require. Such knowledge would require 100% understanding of nutrition and all the sciences (chemistry, physics, physiology, biochemistry, etc.) that underlie it. Such a bold claim is, of course, absurd. If 100% is not known, which it is not, then any claim about precisely how much of a specific nutrient a pet (or person) needs cannot be known either.
Another problem is that no two creatures are the same. Nutritional needs vary like fingerprints. This is called biochemical individuality. Any supposed requirement taken from a chart out of a nutrition text is a statistical average. Your pet may require more or less than this average number and it would pretty much be impossible to know unless specific studies were done on your pet. But that never happens; rather your pet is just plugged into this average number. Depending on nutritional averages to feed your pet is like strapping 100 pounds to your back and wading across a stream with an average depth of three feet. Would you make such a venture?
Also consider how these "requirements" are arrived at in the first place. Scientists will study caged animals in a lab (an unnecessary cruelty) by feeding them a defined maintenance diet where they know the amount of every nutrient. They will then alter one nutrient to see how little will result in deficiency signs, or how much will create toxicity. That's how they create a % requirement for that nutrient. (See Animal Testing and Feeding Trials.)
But here's the problem with this so-called "science." The rules keep changing as to what the base maintenance pet diet should be. The National Research Council that sets these standards keeps changing its mind as to how much of which nutrients should be in this base maintenance diet. Once they change the base diet, all the studies that have been done up to that point determining percent requirements using that base diet are invalidated since there would be no way of knowing if the nutrient being tested was causing the deficiency or toxicity, or if it was the faulty base diet that was used before the revision. But do scientists start all over and reevaluate all nutrients once the base diet is changed? No. Too costly and too much work. They just let their charts remain even though they have now become totally invalid.
It's kind of like having a law that makes it a felony punishable by jail time to jaywalk. Let's say one prisoner appeals, takes it to the Supreme Court and gets released because the Court found the law to be unconstitutional. But all the other jaywalkers are just left in prison. Resetting the percentage standard for any nutrient makes all the other nutrient standards "unconstitutional," automatically in error. But they are all just kept in the "imprisonment" of error anyway.
The point is, so-called official percentages are just guesses. They are erroneous conclusions based upon erroneous premises and data. They are most certainly not good science nor the road to health.
Why have we ever gotten into this situation where we think we need a nutritionist to tell us how much of which nutrient we need? Not one of the trillions of creatures that live on Earth approaches nutrition in this way. Are we smarter than they are? Are our brains superior to Mother Nature? How come we don't see all these creatures dying off from deficiencies and toxicities? Not only do we not see this happening – provided there is adequate natural food supply – they have pretty much robust and disease-free lives. But not so us and our pets, who now spend a large portion of life diminished with a host of chronic degenerative diseases such as cancer, heart disease, dental disease, arthritis, autoimmunities, obesity, diabetes and the like.
The need for accurate percentages of nutrients only arises if a single food is being fed. But that should never be the case. The only percentage that is important in nutrition is the percentage of the diet you are feeding as I have just explained: if 50% of the meals are varied, fresh and natural and 50% of the time you are just pouring a single food in a bowl, that is better than only 10% of the time feeding properly and 90% of the time forcing your pet to eat meal after meal what it would never eat in the wild (most processed pet foods). Remember, I am saying "percentage" here not literally – it is all relative, and the closer to natural feeding, the better.
So don't be misled. Finding a diet with a certain percentage of sodium, potassium, calcium, protein, taurine, carbohydrate, saturated fat and the like and feeding that exclusively is not the road to health. It may seem real scientific and sophisticated but it is the opposite. Let nature, not a silly number, be your guide.