In the first post on this subject we addressed pet nutrition's back story.  To wit: a) why so many veterinarians have a bugaboo about pet food switching, and b) how the one-bag-for-life mantra served to establish a beachhead in the battle for pet owners’ dedication to one brand of pet food over another. In this post we get to the meat of the matter. Why might you want or have to play round robin with your pet foods? 

(At the outset, let me again apologize to all those non-commercial feeders for whom this three-post series has got to seem like either a total yawn or an opportunity to evangelize.)

Here’s how I see it:

If variety is a virtue when it comes to nutrition, it stands to reason that the one-formula-for-life approach might be problematic for our pets. One kind of food, it would seem, is unlikely to meet all of the needs a complex organism (such as our pet) would require over a lifetime.

Nonetheless, pet food manufacturers have gone to great lengths to devise formulas that are "100% nutritionally balanced" to best meet the needs of dogs and cats. Decades of research and multiple pet lifetimes of testing have gone into the majority of these foods. Formulas are revised and refined constantly.

The problem is this: If we’ve undertaken thousands of times more research on human nutrition and still can’t decide what’s best for us, does it not stand to reason that a "nutritionally balanced" diet for our pets might elude modern science as well?

It’s for this primary reason that I recommend the occasional formula change.

It’s not much to do with my nutrition schooling, really; rather, it's just one of those commonsensical deductions I’d like to think of as fundamental. And yet, I’ve been roundly criticized by some colleagues for taking this position.

Given the lack of evidence to support the benefit of formula variety for optimum nutrition and the preponderance of evidence for their digestive drawbacks, they say, my recommendations smack of irresponsibility. (Raw feeders: Does this argument sound familiar?) Nonetheless, I stand by the reasonable assumption that variety is a good thing.

But let’s say you’re still sitting with my detractors on this one. Even so, can we not all agree that there are very good reasons to undertake dietary changes?

Indeed, veterinarians are often the first to recommend you offer new foods, as in the case of therapeutic diets, food trials for skin allergies (here's a post on that), and intolerances (as mentioned in Wednesday’s post on vomiting in cats).

To that end, here’s my list of the top ten reasons a diet change might prove worthwhile, necessary and/or unavoidable:

1. Variety (I repeat myself).

2. Food allergies that manifest in the skin (reportedly the third most common skin disease in dogs and cats).

3. Non-cutaneous food allergies (as when the body’s immune system overreacts to a normal food, as with gastrointestinal disorders like inflammatory bowel disease).

4. Food intolerances/sensitivities (these have a non-immune basis, as with lactose intolerance in humans in which we lack a basic enzyme).

5. Gastrointestinal motility disorders (as with megaesophagus, among other not-uncommon conditions).

6. Chronic illnesses (think: renal failure, urinary stones, liver disease, heart disease, and geriatric conditions).

7. Food recalls and formula changes (they can and do happen).

8. Hurricanes, earthquakes, tornadoes, Costco closing early, and other acts of God (they can and do happen, too).

9. Because you don’t want a pet so gastrointestinally wedded to any one formula that any deviation from it leads to a lake of fetid, mucoid goo (guest-feeding and garbage-eating do happen, you know).

10. Because how can you honestly say, "My pet eats "X" and he’s always done great!" unless you have something to compare it to?

Note that I did not include: "Because he gets bored of his food and refuses to eat." While this may indeed play a role for some animals, I have a hard time believing that the vast majority of animals are not simply playing their people for better fare. (Indeed, most of my patients who suffer "chronic finickiness" are overweight or obese. Explain that.)

OK, so now that we’re done with why, we can move on to how. Tomorrow. Stay tuned.

Dr. Patty Khuly

Pic of the day: "a dog eating bananas" by