So many things...
There is a question I get on a fairly regular basis, which kind of kills me a little every time I hear it. Because I am a sadist, I will share my slow pain with you.
The question comes in several variations, but all of them can be condensed down to: "what would my pet eat in the wild/naturally?"
Despite intention, this is not, for many reasons, the same question as "what is the best thing to feed my pet?"
Here are some of those reasons:
1: Your pet, unless you have some random non-domestic exotic pet, would not exist in the wild/is not a creation of nature. Yes, chihuahuas are genetically very similar to wolves. Well, humans are just as genetically similar to chimpanzees, but very few folks think we should all eat termites and leaves; where's the consistency there? In related news - some of the biggest genetic differences between wild dogs/wolves and domestic dogs is in their ability to digest starches.
2: Nature is a cruel bitch, and the lives of animals in the wild are typically short and brutal, with a lot of time spent on the verge of starvation. Yes, it is rare (though hardly unheard of!) to see age-related diseases such as as diabetes or cancer in wild animals. There are a couple of factors to that - most individuals die before they are old enough to develop those disease, or die very early in the development of them because chronic disease debilitates them enough to lead to death.
3: What most people who ask this question are wanting from me is permission/validation for feeding a raw meat diet. That usually means some combination of chicken and beef muscle meat, maybe with some egg shells or bone in. So turn that back around and logic it out - supposing your cat WAS wild, do you really think it'd be eating cow? How exactly would it be coming by that? You wanna feed a natural diet? feed live whole mice and chicks.
4: Myth: dogs and/or cats are predators, they don't need plant matter/can't digest plant matter. Really? Then why is it that intestine is the first thing many predators go for (assuming they don't just eat their prey whole)? To get the partially digested plant matter and all the nutrients therein, that's why. Commercial diets replace that by 'digesting' the plant ingredients through cooking.
5: Related myth: corn (or wheat, or brewers yeast, or bi-products, or gluten, or whey, or other evil-food-ingredient-of-the-week) is indigestible and will cause all manner of problems. This is only true inasmuch as allergies are a thing that happens. Allergies are a product of an over-reactive immune system, and that over-reactive tendency will be triggered by proteins commonly seen. Since corn, wheat, beef, and chicken are the most common protein sources in commercial pet foods, they are not-coincidentally associated with most of the food allergies we see. That's not the fault of the proteins, it's the fault of the immune systems being exposed to them. Guess what? When people started using lamb and rice more to try moving away from chicken and corn, we started seeing increasing incidence of allergies to rice and lamb.
6: In the wild, animals eat raw things all the time, so my dog/cat is naturally immune to salmonella/e coli/campylobacter, so food borne illness isn't a concern with raw pet diets. Sorry, no. A healthy adult animal does have a much lower likelihood of becoming seriously ill than a puppy/kitten, old, or otherwise debilitated animal exposed to pathogens. So does a healthy adult human - that's why so many food borne illness outbreaks disproportionately affect children and the elderly. And even if your dog doesn't appear ill, that doesn't mean you can't get sick from handling the food/contaminating your kitchen, or that the apparently healthy animal isn't shedding bacteria to contaminate your yard and get your kids sick.
7: It is EXTREMELY difficult to formulate a balanced homemade diet, and even more difficult if you want 'meat only'. Yes, it can be done, but it's generally expensive and time-consuming, and reliably formulated recipes are hard to come by. 'Meat only' is a particular problem because so often that means 'muscle meat only'; there are very few minerals or vitamins in muscle meat - unless that 'meat only' diet includes internal organs, nervous tissue, and bone, you are asking for huge nutritional deficiencies, especially in growing animals.
So the short answer to the question people ask: In the wild, your pet would most likely eat whatever scraps of anything it could find in the few days it had before being eaten by an owl or coyote.
The short answer to the question people should ask: You should feed a formulated, balanced diet from a reputable brand, intended for the species of your pet. That usually means middle-price-range commercial kibble or cans. Not the cheapest thing you can get (usually packed with unnecessary food coloring and low-quality ingredients), nor the most expensive 'designer' or 'premium' options (often overpriced with no related increase in quality, boasting semi-meaningless marketing terms like 'human/food-grade', 'all natural', or 'whole ingredient').
The question comes in several variations, but all of them can be condensed down to: "what would my pet eat in the wild/naturally?"
Despite intention, this is not, for many reasons, the same question as "what is the best thing to feed my pet?"
Here are some of those reasons:
1: Your pet, unless you have some random non-domestic exotic pet, would not exist in the wild/is not a creation of nature. Yes, chihuahuas are genetically very similar to wolves. Well, humans are just as genetically similar to chimpanzees, but very few folks think we should all eat termites and leaves; where's the consistency there? In related news - some of the biggest genetic differences between wild dogs/wolves and domestic dogs is in their ability to digest starches.
2: Nature is a cruel bitch, and the lives of animals in the wild are typically short and brutal, with a lot of time spent on the verge of starvation. Yes, it is rare (though hardly unheard of!) to see age-related diseases such as as diabetes or cancer in wild animals. There are a couple of factors to that - most individuals die before they are old enough to develop those disease, or die very early in the development of them because chronic disease debilitates them enough to lead to death.
3: What most people who ask this question are wanting from me is permission/validation for feeding a raw meat diet. That usually means some combination of chicken and beef muscle meat, maybe with some egg shells or bone in. So turn that back around and logic it out - supposing your cat WAS wild, do you really think it'd be eating cow? How exactly would it be coming by that? You wanna feed a natural diet? feed live whole mice and chicks.
4: Myth: dogs and/or cats are predators, they don't need plant matter/can't digest plant matter. Really? Then why is it that intestine is the first thing many predators go for (assuming they don't just eat their prey whole)? To get the partially digested plant matter and all the nutrients therein, that's why. Commercial diets replace that by 'digesting' the plant ingredients through cooking.
5: Related myth: corn (or wheat, or brewers yeast, or bi-products, or gluten, or whey, or other evil-food-ingredient-of-the-week) is indigestible and will cause all manner of problems. This is only true inasmuch as allergies are a thing that happens. Allergies are a product of an over-reactive immune system, and that over-reactive tendency will be triggered by proteins commonly seen. Since corn, wheat, beef, and chicken are the most common protein sources in commercial pet foods, they are not-coincidentally associated with most of the food allergies we see. That's not the fault of the proteins, it's the fault of the immune systems being exposed to them. Guess what? When people started using lamb and rice more to try moving away from chicken and corn, we started seeing increasing incidence of allergies to rice and lamb.
6: In the wild, animals eat raw things all the time, so my dog/cat is naturally immune to salmonella/e coli/campylobacter, so food borne illness isn't a concern with raw pet diets. Sorry, no. A healthy adult animal does have a much lower likelihood of becoming seriously ill than a puppy/kitten, old, or otherwise debilitated animal exposed to pathogens. So does a healthy adult human - that's why so many food borne illness outbreaks disproportionately affect children and the elderly. And even if your dog doesn't appear ill, that doesn't mean you can't get sick from handling the food/contaminating your kitchen, or that the apparently healthy animal isn't shedding bacteria to contaminate your yard and get your kids sick.
7: It is EXTREMELY difficult to formulate a balanced homemade diet, and even more difficult if you want 'meat only'. Yes, it can be done, but it's generally expensive and time-consuming, and reliably formulated recipes are hard to come by. 'Meat only' is a particular problem because so often that means 'muscle meat only'; there are very few minerals or vitamins in muscle meat - unless that 'meat only' diet includes internal organs, nervous tissue, and bone, you are asking for huge nutritional deficiencies, especially in growing animals.
So the short answer to the question people ask: In the wild, your pet would most likely eat whatever scraps of anything it could find in the few days it had before being eaten by an owl or coyote.
The short answer to the question people should ask: You should feed a formulated, balanced diet from a reputable brand, intended for the species of your pet. That usually means middle-price-range commercial kibble or cans. Not the cheapest thing you can get (usually packed with unnecessary food coloring and low-quality ingredients), nor the most expensive 'designer' or 'premium' options (often overpriced with no related increase in quality, boasting semi-meaningless marketing terms like 'human/food-grade', 'all natural', or 'whole ingredient').