If my dog could talk, here's what he would say: “More peanut butter, please.”

It's clear that dogs love the stuff; what’s not so clear is why.

Fat or Sugar or Salt?

Most peanut butter has gobs of fat, sugar and salt — all easy things for a dog to like. But is that really why they love it so much?

Although dogs seem to crave salt, and will lick your fingers if you've been eating chips, they’re not as turned on by it as humans are. Because they lack salt-specific taste buds, they don’t crave it like we do. Nor is it something they particularly need. In the wild, more than 80 percent of a canine’s diet comes from meat. Humans might deem raw meat as rather bland, but it contains more than enough sodium for a dog. Most dog foods also have plenty of salt. Besides, natural peanut butters often have no added salt and dogs seem to love them just as much.

What about fat? Peanut butter is full of it. And fatty foods do seem to taste better — a fact as true for dogs as it is for humans. Indeed, it may be truer for dogs because they have more fat-related taste buds than we do. Does that make fat the key to peanut butter's appeal? Not quite. The extra buds seem to apply only to fats that come from meats — not from vegetables or legumes. And there are plenty of other high-fat foods that dogs don’t like, especially ones they have a hard time digesting.

What about sugar? Unlike cats, dogs have a sweet tooth — or a sweet tongue, actually. They respond positively to the chemical furaneol, a flavor that cats are basically “blind” to. Indeed, “sweet” is something dogs can smell. And the furaneol taste buds are concentrated on the tip of a dog’s tongue. If they’re licking peanut butter out of something, like a Kong toy, that’s perfect placement for maximum contact. The problem is that dogs seem to like natural, no-sugar-added peanut butters just as much as Jif or Skippy. As with salt, the only sugars comes from the actual peanuts.

The Lure of Protein

All that’s left is protein. Peanut butter is loaded with the stuff. In fact, that’s why it was created in the first place, by a doctor looking for a high-protein, easy-to-digest food for his patients. Those two qualities — high protein and easy to digest — might be just the clues we’re looking for.

Although dog owners may worry that too much protein is bad for their pups, causing joint problems or even kidney damage, there’s really not much to worry about. Anti-protein claims have largely been proven false. In fact, growing pups need fairly high amounts of protein. As long as a grown-up dogs' kidneys are fine to begin with, they shouldn’t have any trouble removing excess protein from the body.

In fact, your dog needs plenty of protein to help replace skin and hair, which its body does constantly. A healthy coat is often a sign of sufficient protein in a dog’s diet, while brittle fur and bald patches point to a protein deficiency. Protein is also a big part of your dog’s immune system. And if you have a working breed, the dog will need even more protein to stay healthy while being active. But lots of dog foods are low protein because of old concerns. If dogs have a protein deficiency, they may look for it elsewhere. They find a quality source in peanut butter.

Other than from meat, it can be hard for dogs to find high-quality, easy-to-digest proteins. Most herbivorous foods have a starchy type of protein that can't easily be used by the body. Peanut butter is an exception. As noted by the doctor who invented the stuff, peanut butter’s protein is easy to digest — and not just for humans. Dogs tend to have a taste for foods they need.

In the end, the question might not have just one answer. It might be a little bit of everything: salt, sugar, fat and protein.

Or maybe the answer is very simple: Dogs love peanut butter because it’s fun to eat. When put in the right toy, it can make dogs lick their lips for hours.