Delaney founded BalanceIt, a website with tips on preparing pet food and other finer points of pet nutrition, in 2005. Interest in homemade pet food really took off in 2007 after the melamine pet food scare, he says, and is still growing.

Bob Loper, a former freelance writer who lives in Washington, D.C., says he started cooking food for Toffee, his 10-year old mixed Boykin spaniel, during "a very itchy phase." The vet told him she was allergic to something in the environment, her food or their home.

After eliminating the possibility of fleas, he decided to try a dog food recipe his wife found online. The recipe was created by Michael Fox, former vice president of the Humane Society of the U.S. and the author of more than 40 books on animal care, behavior and bioethics.

The dish is basically a hamburger and rice casserole, with a few extra nutrients thrown in, like brewer's yeast for minerals like chromium and selenium.

"I am an advocate of whole, organic foods that are biologically appropriate for the species. Food for Dogs is different from 'Dog Food' — it's human food quality, but with less grains," Fox writes on his website, where he offers the dog food recipe, plus organic and GMO-free prepared pet food products.

Many people assume that the most "biologically appropriate" food for dogs is meat, but it's more complicated than that. Domestic dogs evolved from wolves, who are carnivores, but recent research published in the journal Science shows that as domesticated dogs evolved along with people, they became omnivores.

As people began to settle down and farm, dogs came along for the free food. And it was rarely meat — it was scraps of grains and vegetable waste on the dump heaps. Dogs that developed the ability to digest starch had an advantage, researchers say.

Cats are another story – they are dedicated carnivores, as you may have noticed when they show up at the door with half-dead mice and birds as presents.

Yet grains – how much and what kind — have become a controversial issue in recent years in both human and pet diets. These days, most complete and balanced pet-food products contain grains, according to Marion Nestle, who authored a book on pet food in 2010.

But as humans have become increasingly concerned that grain-based carbs are the reason we're fat, some pet owners worry our dogs and cats who eat commercial pet food might also be gaining too much weight from the grains in it. That's led many pet owners to look for alternatives.

According to Fox, sales of grain-free pet foods jumped some 28 percent between 2011 and 2012 — to $1.4 billion for dog food, and some $322 million for cat food. Yet it's a small drop in the food bowl. Pet food is a $21 billion a year market.

Some pet owners are even putting pets on raw food diets, which makes Joni Scheftel, state public health veterinarian at the Minnesota Department of Health in St. Paul, nervous because it may increase human exposure to salmonella and other foodborne illnesses. (More on that tomorrow.)

Cooking your own food for Fido is fine, vet nutritionist Delaney says, as long as you learn the dos and dont's. First of all, dog food can't contain ingredients pets can't tolerate, like garlic and onions, raisins, grapes and kabocha squash, he says. And you need to know the right proportions of protein and essential fatty acids. "You have to do math ... to make sure it's balanced," he says.

For example, dogs can only handle a certain amount of vitamin D, or they can develop renal and urinary problems from hypercalcimia. There have also been reports of broken bones from inadequately balanced homemade diets, as reported in a review published in the Journal for American Veterinary Medical Association in 2012.

While it's a lot of work to do it right, many owners who cook for their dogs say the proof is in the poop. Two years after she started on a homemade diet, Toffee's stopped scratching, her coat is shiny, and she make about 50 percent less poop that has to be scooped, Loper says. And she loves her food.

Loper says the reason more people like him are turning away from commercial dog food is that they are choosing fresher, more natural food ingredients for themselves these days. And they want to do the same for their companion animals.

"If you're making better food for yourself, and cooking, why not [cook dog food]?" he says. "It's practically as quick as making pasta."

Copyright 2014 NPR.

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