A website called “Raw Feeding Community” attempted to put this question to bed once and for all, so they conducted an experiment with a dog being fed kibble and raw food separately, about 10 days apart. Both meals were consumed with barium, so that the movement of the food through the digestive tract could be radiographed and timed. Since the kibble exited the body faster than the raw meal, the website declared that their experiment offered evidence that there is no truth to the oft-repeated admonition that kibble and raw should not be fed together because kibble digests slower.
Is the experiment valid?
Firstly, although it’s an interesting exercise, I don’t think any experiment that involves only one dog can be used to prove anything except what happened in that particular instance with that particular animal. If the experiment was replicated 20-30 times with different dogs and different types of foods and yielded the same result, we could begin to take it seriously. Apart from that, it is known that barium can cause constipation, so we don’t know from this experiment how either of these two foods would perform without the barium. In addition, considering how unpleasant some of the side effects of barium are and how little useful information this experiment ultimately provided, one has to wonder if it was worthwhile putting an innocent dog through it.
Mixing causes problems, it cannot be denied
Secondly, the negative experiences of thousands of transitioning raw feeders who attempt to mix kibble and raw cannot be dismissed with one experiment. Personally, I did this once with a dog about 17 years ago and the result was an extremely unpleasant and messy bout with both diarrhea and vomiting. That was the last time I mixed kibble and raw. I have since transitioned dozens of dogs, and instructed hundreds of new raw feeders how to transition their dogs, and have never had the experience again.
Does it even matter which digests faster?
Obviously, there is more to the question of whether kibble and raw can or should be mixed than the speed with which either goes through a dog’s system. In fact, it may have nothing to do with transit time at all. Simply combining foods of different constituent make-up is problematic for dogs, who have a single chambered stomach which can only produce one type of chemical environment at a time. Generally, foods that require an acidic environment (such as protein) to be broken down should not be mixed with foods that require an alkaline environment (such as carbohydrates). When they are, the two different chemistries neutralize each other, and a good percentage of the food becomes waste rather than nourishment.
Most commercial pet foods combine many incompatible foods, and that’s one reason why they are so unhealthy for dogs. That’s only part of what’s going on when kibble and raw cause issues when fed together, however. It’s not the digestive process that primarily causes problems, it’s the decomposition process.
The putrefaction problem
Raw food rots, kibble does not. (If you doubt that, leave a pile of each sitting on your counter for a week.) If the digestion of kibble takes longer than it takes the accompanying raw food takes to decompose, the body may find it necessary to eject both foods. Historically, dogs have been able to digest food that is in a putrefied or partly putrefied state. However, even dogs have their limits. There are some foods and combinations of foods that they cannot digest. The body may simply decide that the mess created by all the ingredients of the kibble in addition to putrefying raw food is better discarded than absorbed. That’s one reason why any experiment aimed at answering the above question would need to be done with many different kinds of kibble. Grains and raw meat together create a digestive nightmare for a dog, for example, so a grain-based food might be more of a problem than a grain-free one (although it should be noted that even so-called grain free foods often contain lots of carbohydrates).
“Cost” vs. benefit
Both vomiting and diarrhea are very costly to the body, in terms of energy and fluids. The benefit has to be equivalent or greater than the cost in order for the body to expend its resources. In the case of vomiting or diarrhea that results from kibble and raw being combined, that benefit is a decrease in potential damage caused by absorption of the toxic by-products of putrefaction, or the inability of the body to make use of enough of the usable food to make it worth eliminating the unusable. The body does not make a mistake when it seeks to rid itself of indigestible food, so we have to conclude in those cases that benefit exceeded cost, even if we are never able to know with 100% certainty what the benefit was. Our goal is to make as few feeding mistakes as possible, so as to remove the body’s need to protect itself.
Vitality vs. tolerance
The bigger question is not whether raw food or kibble digest quicker, but why it is that some owners seem to ‘get away’ with combining them. It may relate to the make-up of the kibble being fed. Or it may have more to do with the typical kibble-fed dog’s lack of vitality, because it takes energy for the body to conduct the emergency rejection of a food. Think of the analogy of a young child immediately spitting up after drinking a jigger of alcohol. The body of a child has a great deal more of his/her original vitality with which to protect itself than an adult who regularly drinks alcohol. The latter represents tolerance, and tolerance always exacts a price on the vitality of the organism.
Gradual transition is not necessary
The bottom line is that there is never any reason to mix kibble and raw food. Misguided attempts to transition a dog to raw feeding by dribs and drabs are not necessary when you understand all the dynamics involved. Transitioning a dog to raw feeding is the #1 thing you can do to ensure a long healthy life free of vet visits for your dog, and there’s no reason to delay or do it gradually. When you finally learn that what you’ve really been feeding your dog is garbage, there’s no reason to continue feeding it for even one more day.
Full instructions on how to successfully and cleanly transition a dog to raw feeding are contained in my booklet.