DIGEST THIS: Kibble May Actually Digest Faster Than Raw

As raw feeders, we’ve all heard the ominous warning to “never mix kibble and raw because kibble digests slower than raw.” Where did this sage piece of advice originate, and is there any truth to it? Why are dogs so commonly advised to suffer through a “detox phase” consisting of raging diarrhea and vomiting, if they could be slowly transitioned from kibble to raw in the same manner that is recommended to switch between kibble varieties? The Raw Feeding Community decided to put this myth to the test, and the results of our “experiment” may surprise you…

The Usual Advice
Scanning the top holistic and raw feeding groups and forums, one will find the same advice and explanation listed time and time again. A search of “switching from kibble to raw” on the Dogs Naturally website brings up the follow information:

“I recommend you feed dry or canned food separately from dehydrated or raw meals because they digest at different rates.” (1)

The first time I came across this tip, I remember thinking to myself, “Why does this matter?”, so I read on. This statement is usually followed up with an explanation along the lines of, “raw food digests faster than kibble and mixing them together will cause raw food to sit in the stomach too long. This makes the body more likely to contract bacteria from the raw food.”

Does raw really digest faster than kibble? We posted a thread asking the members of The Raw Feeding Community how long it takes kibble to digest, and received some interesting, although extremely inconsistent, answers. Some claimed kibble took as little as 2 to 3 hours to digest, yet there were a surprising amount of answers that claimed kibble took as much as 16 to 18 hours!

However, even if the digestion rates of kibble and raw differ, this explanation still doesn’t make much sense from a scientific standpoint. That just isn’t how the digestive system works; especially the short, acidic digestive system of a carnivore. And isn’t part of the argument for raw feeding that our carnivore’s bodies are designed to handle the large amounts of bacteria associated with consuming raw animal products? What about raw food would make it more likely to digest faster than kibble? Why would gastrointestinal transit time affect bacterial susceptibility? We know that candy goes through the body faster than a strawberry; aren’t manufactured products supposed to digest more quickly than their raw, uncooked counterparts?

Many people have successfully fed raw and kibble together for years without issue. In fact, feeding raw and kibble together is very common for sled dog teams (here is a cool video of what an Iditarod sled team is fed during the race). It seems to be only relatively recent advise to avoid this kind of feeding. Why should owners be advised to avoid mixing the two? Wouldn’t some raw be better than no raw at all? The Raw Feeding Community decided to find out where this advice could’ve possibly originated from, and if there were any amount of truth to it.

Our Test Dog
For our experiment, we used a 16 month old, intact male, raw fed borzoi who was weaned to partial raw and has been kept on a raw diet throughout his life (prey model raw with occasional supplements). A barium series was performed on December 18, 2014 feeding a kibble meal, and on December 27, 2014 feeding a raw meal. Barium is a radiopaque liquid which can be mixed with food and used to enhance visibility of the gastrointestinal tract on X-ray.

Our test dog
Our test dog, Jaeger.

The Kibble Used
For the kibble study, 2 cups of Science Diet Large Breed Adult kibble was mixed with ½ cup of Science Diet I/D canned and 20mls of barium liquid. Approximately 1 ½ cups of kibble and ½ can of food were consumed over a span of 5 minutes. Thirty minutes later, cranial (top half of the GI tract) and caudal (bottom half of the GI tract) abdominal and lateral (laying on the side) abdominal radiographs were performed. Radiographs were repeated at 1hr, 2hrs, 3hrs, and 4hrs until the stomach was empty (2).

The Raw Used
For the raw meal, 1 cup of bison and green tripe grind (3), 1 cup of chicken gizzards, and 1 chicken drumstick mixed with 20mls of liquid barium were offered over 5  minutes. Approximately ½ of the meal was consumed (including only ½ of the drumstick.) Thirty minutes post-feeding, cranial and caudal abdominal and lateral abdominal radiographs were performed. Radiographs were repeated at 1hr, 2hrs, 3hrs, 4hrs, and 5hrs until the stomach was empty.

Results
Going into this case study, I expected raw to digest more quickly than kibble, simply because I expected there to be some shred of truth to all of the information provided by knowledgeable raw feeders. I personally hypothesized that there would not be a significant (greater than 3 hour) difference between the time it took the food to move from the stomach into the large intestines.

Digestive Anatomy and Physiology Review
Before going into detailed results, it helps to have a basic orientation of what you are looking at and what exactly is happening as food moves through the body. Below are cranial and caudal lateral abdominal x-rays with the major body parts labeled.

Figure 1. Labeled to show the major organs and structures as viewed radiographically. These x-rays were taken 30 minutes after feeding a kibble meal (mixed with barium).
Figure 1. Labeled to show the major organs and structures as viewed radiographically. These x-rays were taken 30 minutes after feeding a kibble meal (mixed with barium).

Carnivores have the shortest gastrointestinal tracts of any mammal. Food breakdown in all mammalian species begins in the mouth where salivary enzymes are released and mechanical digestion is initiated by the tearing and grinding of food. With carnivores, the majority of food breakdown is accomplished by the stomach and intestines as opposed to omnivores and herbivores who rely on more “intense” mastication to “break down” their food.  Food travels from the mouth, into the esophagus, and reaches the stomach in a matter of seconds.

Once in the stomach, the real work begins. Chemical digestion of proteins is initiated by enzymes like hydrochloric acid, pepsin, and lipase and food is liquidized. Hydrochloric acid is the enzyme responsible for denaturing proteins, eliminating bacteria, and converting other enzymes. Pepsin is solely responsible for protein digestion and lipase, which is only found in the stomach of carnivores, begins digesting fats (carbohydrate digestion begins in the mouth with the addition of the enzyme amylase) (4).

After being turned into liquid, food begins to leave the stomach via a sphincter in a region called the pylorus. The first segment of the small intestines, the duodenum, contains the openings of the pancreatic duct and the common bile duct (gallbladder). Bile and pancreatic enzymes are critical for the absorption of fats, carbohydrates, and proteins. The duodenum is the shortest segment of the intestines, but due to the addition of these critical enzymes, it is where the majority of chemical digestion takes place.

The next segment of the small intestines, the jejunum, is also the longest, and is where the majority of nutrient absorption and continued chemical digestion takes place. The surface of the jejunum is covered in small, finger-like projections called villi, which serve to increase the surface area for food absorption (5). The final section of the small intestines, the ileum, serves as a final place for digestion – in herbivores, the ileum contains a high-functioning cecum and plays a much more critical role.

Finally, food moves into the large intestines (colon). In carnivores, this is where water is absorbed, bacterial fermentation takes place, and feces are formed.  Now that we have visually seen the anatomy and followed food on its path through the gastrointestinal system, we will move on to the actual results of our “experiment.”

Thirty Minutes Post Feeding

  Figure 2. Cranial view of abdomen 30 minutes post feeding a kibble (left) and a raw (right) meal.
Figure 2. Cranial view of abdomen 30 minutes post feeding a kibble (left) and a raw (right) meal.
Figure 3. Caudal view of abdomen 30 minutes post feeding a kibble (left) and a raw (right) meal.
Figure 3. Caudal view of abdomen 30 minutes post feeding a kibble (left) and a raw (right) meal.

After 30 minutes, we see both stomachs moderately distended with food and barium. With the kibble meal, the food and barium has settled into the pylorus (bottom of the stomach) and is moving into the small intestines. There is negligible amounts of barium moving into the small intestines with the raw meal because there is likely a large portion of meat preventing the barium from filling the entire stomach and moving out.

 One Hour Post Feeding

Figure 4. Cranial view of abdomen 1 hour post feeding a kibble (left) and a raw (right) meal.
Figure 4. Cranial view of abdomen 1 hour post feeding a kibble (left) and a raw (right) meal.
Figure 5. Caudal view of abdomen 1 hour post feeding a kibble (left) and a raw (right) meal.
Figure 5. Caudal view of abdomen 1 hour post feeding a kibble (left) and a raw (right) meal.

One hour post feeding, when can see the diameter of the stomach starting to decrease and the small intestines are filling with barium. Movement from the stomach into the small intestines is much more dramatic with the kibble meal than the raw.  In both cases, we can begin to see feces (not highlighted with barium) being formed in the large intestines – remains from his previous meal.

Two Hours Post Feeding

Figure 6. Cranial view of abdomen 2 hours post feeding a kibble (left) and a raw (right) meal.
Figure 7. Caudal view of abdomen 2 hours post feeding a kibble (left) and raw (right) meal.
Figure 7. Caudal view of abdomen 2 hours post feeding a kibble (left) and raw (right) meal.

At 2 hours post feeding, the difference in the rate at which food has left the stomach and entered the small intestines (jejunum) between the kibble and raw fed meals is undeniable. The kibble meal is moving into the intestines faster than the raw meal. Formed feces in the colon are becoming more obvious.

Three Hours Post Feeding

Figure 8. Cranial view of abdomen 3 hours post feeding a kibble (left) and a raw (right) meal.
Figure 8. Cranial view of abdomen 3 hours post feeding a kibble (left) and a raw (right) meal.

Three hours post feeding our kibble meal has mostly left the stomach, filled the small intestines, and is moving into the large intestines. It is safe to say that kibble has completely left the stomach by 3 hours – a far cry from what is usually claimed. Movement with the raw meal is definitely slower, but we can see decreased opacity in the stomach and definite movement of feces through the colon. Unfortunately, the caudal kibble radiograph was somehow lost so it is not available for comparison.

Four Hours Post Feeding

Figure 9. Cranial view of abdomen 4 hours post feeding a kibble (left) and a raw (right) meal.
Figure 9. Cranial view of abdomen 4 hours post feeding a kibble (left) and a raw (right) meal.
Figure 10. Caudal view of abdomen 4 hours post feeding a kibble (left) and a raw (right) meal.
Figure 10. Caudal view of abdomen 4 hours post feeding a kibble (left) and a raw (right) meal.

At four hours post feeding, you begin to notice a drastic difference in the amount of ingesta left in the kibble verses raw photos. Although the same amount “went in” with both meals, there is significant less food in the intestines with the raw meal. I’ll talk about why that difference is important in the discussion.

Five Hours Post Feeding

Figure 11. Cranial and caudal view of abdomen 5 hours post feeding a raw meal.
Figure 11. Cranial and caudal view of abdomen 5 hours post feeding a raw meal.

For the raw meal, I had time to take a final radiograph 5 ½ hours post feeding. The stomach, surprisingly, still had the bone fragment floating around, but the majority of ingesta was in the colon, as expected.

Discussion
In conclusion, the raw meal appears to have digested slightly slower than the kibble diet. When you really think about it, it makes total sense – and it is great news for our dogs, and for us raw feeders! Here is why:

  • The first reason is obvious – this means that little credence can be given to the claim that mixing raw and kibble is harmful to your pet because raw sits in the stomach longer. Rarely, a dog does not tolerate a mixed kibble and raw meal, but it has nothing to do with digestion rates. Any kind of sudden diet change typically results in digestive upset; it is not exclusive to feeding raw and kibble together.
  • Also worth mentioning is the bone fragment that stayed behind more than 5 hours after feeding, implying that whole bone takes much longer still to digest. This implies that raw meaty bones will take even longer to digest than the ground raw with bone that was used in this experiment. This makes sense, as a whole bone will obviously take more time to break down than ground bone, which was already broken down before the dog ate it. The ground raw that this dog ate also only contained 10% bone, while the chicken drumstick would have a much higher bone content.
  • By mixing raw and kibble during the transition period, your dog is less likely to experience the diarrhea and vomiting associated with “detox.” It is commonly recommended to slowly transition (over a period of 10-14 days) between kibble brands. I personally recommend doing the same with raw to avoid causing diarrhea. What many call “detox” is a normal reaction to a sudden change in diet (dietary intolerance). The pH and flora of the stomach change when a dog is fed a raw diet, so slowly transitioning gives the body time to adjust. The way I recommend transitioning is to slowly start with small pieces of raw (chicken is often best) while decreasing the amount of kibble over a period of two weeks. After your pet is fully transitioned onto raw, you may then begin adding more components (organs and other proteins) to the diet. You can see our beginner files on The Raw Feeding Community facebook group for more information.
  • If food remains in the intestines longer, more water is absorbed, thus leading to the beloved small raw feces. The reason for big voluminous kibble feces is because there is so much left undigested and unused.
  • Most importantly, remaining in the GI tract for longer periods of time means that the body is able to absorb and utilize more nutrients from the food. Why do raw fed dogs often have shinier coats, less skin issues, and seem to experience a decreased incidence of disease? Because their bodies are better able to utilize the good stuff in raw! Not only do they get the benefit of taking up the maximum amount of nutrients, studies have shown that eating whole foods burn more calories which in turn leads to a fitter animal (6).

Although one animal is by no means enough to declare conclusively that raw digests slower than kibble in every instance, the results strongly suggest that the broad blanket statement that “raw digests faster than kibble” is false. And even if one does digest quicker than the other, it would still have no effect on whether or not they would be safe to feed together.

By conducting this experiment and publishing these results, all we mean to do is encourage people to question everything they are told online, and look for proof rather than anecdotal evidence. There is an unfortunate lack of peer reviewed studies when it comes to raw diets. A lot of what is claimed online tends to be simply hear-say or anecdotal evidence. As raw feeders, we should strive to always continue learning more about what we are feeding our pets, even if what we are learning happens to go against the grain of what most raw feeding Facebook groups preach.

References

  1. http://www.dogsnaturallymagazine.com/switching-dogs-kibble-raw/
  2. http://www.dogfoodadvisor.com/dog-food-reviews/hills-science-diet-dog-food-adult-dry/
  3. Grind produced by Texas Tripe. Made with bison (meat, organs, and bones). Contains approximately 10% fat, 10% bone. texastripe.com
  4. http://www.ncbi.nlm.nih.gov/pubmed/2036471
  5. http://www.peteducation.com/article.cfm?c=2+2083&aid=512
  6. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2897733/

 

 











33 thoughts on “DIGEST THIS: Kibble May Actually Digest Faster Than Raw”

  1. Pingback: Raw food study
  2. it always bothered me that people thought that highly processed, ground and cooked food digested slower..

    Personally I wouldn’t mix raw and kibble because I wouldn’t want the bacteria on the kibble being able to multiply when introduced to the moisture on the surface of the raw..it is why I don’t like mixing kibble and canned food or mixing kibble with water. Do you know how long that kibble sits around? it has an incredibly long shelf life, and the bacteria on it stays under control because it is so dry until it hits the acid of the stomach.. but mix it with something not acidic, those things can grow and flourish..

    Anyway.. thank you so much for doing this study and publishing the results! I am sure quite a few people benefit from it.

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  3. The author of this article should rethink the use of the word “digest” in his headline. Kibble is NOT more digestible than raw. It moves through the digestive tract faster because there just aren’t enough actual nutrients TO digest. Kibble = daily, sometimes numerous, voluminous, somewhat to ghastly smelly poo. Raw = once a day to every two days, small volume, non-smelly poo. Tell me which has been digested better. All this article did was convince me even further that raw feeding is the BEST food to feed our kitties [and dogs]. And sorry, but I ain’t mixing raw with no less-digestible kibble.😀

    Liked by 1 person

    1. Yes… that is exactly what this article says, actually. The article concluded that raw is more digestible than kibble. Maybe you should re-read the last couple paragraphs? Quoted straight from the article… “Why do raw fed dogs often have shinier coats, less skin issues, and seem to experience a decreased incidence of disease? Because their bodies are better able to utilize the good stuff in raw! Not only do they get the benefit of taking up the maximum amount of nutrients, studies have shown that eating whole foods burn more calories which in turn leads to a fitter animal (6)”

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      1. I hear what you’re saying, plearbear. And yes, I agree that raw is more digestible. My only thought is that some just reading the headline, DIGEST THIS: Kibble May Actually Digest Faster Than Raw, are going jump to the conclusion that “kibble is more digestible.” Not all are going to read the article in its entirety–and the headline/title is a bit misleading with regards to ‘digest[ing]’ and therefore what digestion entails (even though it is explained in the article–not all are going to understand or read it). I was thinking perhaps it should say “transit time is faster” instead.🙂 Will say that even with my ‘wording problem’ this is a great article and experiment.

        P.S. I know this is an article for dog caregivers, but in case any kitty caregivers are reading this, this statement “(carbohydrate digestion begins in the mouth with the addition of the enzyme amylase)” is not true for felines. They do not have this enzyme in their saliva/mouth. They are obligate/true carnivores and have no need, and limited physiologic processes, to digest carbs.

        Liked by 1 person

    2. Jules, thanks for your comment! When I say “digest” in the title and description, I am referring to “digest” as the breakdown of food using the simplest form of the definition. Kibble breaks down faster than raw = kibble digests faster than raw. I completely understand where you are basing your recommendation from, but due to the way the alternative myth (raw “digests” faster than kibble) is worded, I thought that this would be a more appropriate and catchy title (and also a bit easier for a lay person to understand.) I will not assume responsibility for anyone too lazy to read through the article and then base their opinion off of the title!

      Thank you for also making mention of the fact that cats do not have salivary amylase (although they DO have several other organs that produce it.) Digestion of starch begins in the stomach (as opposed to the mouth) of cats.

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  4. Would like you to do a study on switching from raw to kibble and back. We switch our dogs on a regular basis when we are away to competitions. We havn’t seen any of the issues you have switching back and forth.

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  5. Thank you for doing all the work required to perform this test. Your posting helped me to decide whether or not I wanted to feed some raw with kibble. “Bacteria” growth with moisture of raw food? I’m not going to research that one at all. When I put tripe in the bowl I usually don’t sit it directly on the kibble .. but the whole entire meal is gone within 5 minutes. Again thank you so much for absorbing the cost of the special X-Rays and doing this experiment.

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  6. Pingback: Raw Bones - Page 2
  7. Hello there thanks for this info – my question would be, does the next meal of kibble prematurely push the still digesting bone through the system? As in, if you feed all raw, everything is on the same digestive schedule. But lets say you fed your dog a meaty bone the night before and in the morning kibble — would the body “speed up” and push through undigested bone in anticipation of moving out the kibble ? My friend feeds his dog a mix of meaty bones and kibble and sees chunks of bone in the poop — whereas my raw dogs poop turns into powder, no chunks of bone at all. Wondering if the reason is rushed digestion of the bone as a result of the kibble and if the bones could cause any damage being passed over time…

    Liked by 1 person

  8. Great read! I think it’s interesting that in English speaking sites about raw, this no kibble with raw ideology seems pretty common, where as where I come from feeding 50/50 raw & kibble is a pretty wide spread way of doing things🙂

    Also, I think that this is interesting from the pov of owning a dog who suffers from acid reflux. We fed her raw before, but she got really bad acid reflux, so we had to feed her low fat cooked fish for a while. Then she got too thin, not a surprise, since pollock hasn’t got that many calories, and now we are feeding her also kibble. I was surprised that kibble didn’t aggravate her acid reflux, but since reading this, I think it’s pretty obvious. Kibble digests fast, hence it doesn’t stay in the stomach long to cause problems!

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  9. in your learned opinion, would you do this, i currently feed taste of the wild kibble, upto 60% meat no fillers or wheat twice daily. about once a week I replace a kibble meal for raw red meat mainly beef, also later that same week il replace a kibble meal with a marrow bone. Stools are different but not loose. Am I unwittingly harming my dogs by feeding the occasional raw meal ?

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  10. Great article. I can see raw and kibble is in the small intestine after 5 hours. How much time is passed whilst the waste then passes into the large intestine then pooped?

    I’m trying to work out the total transit time from ingestion to poop…

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  11. I have actually been one of those that has been believing the whole raw and kibble in the same meal danger. I thought it made sense and all, but had questioned it. I am glad I have found this blog that truly questions and wants to find the truth. I am very excited to find this study and experiment.

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  12. We have a weim that was fed on kibble from bringing him home at 8wks ( we thought we were doing the right thing) All was ok until about 16/18 months them bam, constant scratching, itchy red raw skin dog was miserable. We tried medication and wash. I started to read about raw feeding and watch our dog suffer any longer. I threw out the kibble the next day and immediately put him on prey model raw food twice daily. Couldn’t believe the difference within a week and by 4 to 5 wks scratching totally gone, small poops, drinking less water, glossy soft coat and a much happier weim all round.

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  13. Do you happen to know if any studies have been done till now that compare the transit time of raw, cooked and kibble foods for dogs? I have been searching for that for ages and haven’t come up with anything. In fact, yours is about the only comparison that I’ve found so far. Thanks!

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  14. What about feeding both – kibbles and natural food – in separate meals? I have a puppy (9 w.o.) who was only fed kibbles. Now I’m introducing him to real food. Twice a day he gets boiled chicken and tiny bit of rice (I haven’t tried raw yet). So far, it’s been good. No stomach upsets and he really likes chicken even though he was hesitant at first. Are there any issues with feeding him combination diet long term?

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  15. funny thing is that our leonberger bloated twice within 2 weeks time. Both times his kibble meal from the morning came out undigested,(we were in time to have his stomach pumped) but his most recent (evening) Rawmeal, didn’t. With that knowledge we stopped feeding kibble and he never bloated again and lived for another 2,5 years, died from old age in his sleep.

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  16. I really appreciate this article! We have a rescue puppy who did not like her high quality, grain-free kibble (we suspect she had table scraps most of her puppy life). We aren’t prepared to go raw entirely at this point, but we buy freeze dried raw nuggets and crush it on her kibble, which she finds more palatable. Our trainer told us not to because of variable digestive rates. I’m not a vet but a generally educated human and it sounded like bull- like something people who “cleanse” and think food lives in their intestines for months would believe. I was really happy to find your blog and someone who takes an approach based on science rather than anecdote, and your other articles are similarly informative and thoughtful. I really appreciate being able to learn more about raw from a source that has some data- it must be a lot of work and expense to do that but it is really great for all of us to be able to benefit from that!

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