I recently reported on a study out of Australia that found an association between feeding raw chicken, infection with the bacterium Campylobacter, and a serious neurologic disease call Acute Polyradiculoneuritis (APN). Not surprisingly, advocates of raw diets are desperate to find ways to dismiss this study so they can continue to claim raw diets are as safe, or safer than commercial cooked pet foods. Cognitive dissonance, the discomfort that one feels when confronted with evidence that one’s beliefs about something may be wrong, is a powerful force, and it can lead even smart, educated people to engage in extreme mental gymnastics to dismiss such evidence and preserve cherished beliefs.
Many of the criticisms of the Australian study are simplistic and obviously wrong or irrelevant. It is sometimes dismissed as ”just one study.” This would be a fair criticism if it were true and if there were substantial evidence of benefits to feeding raw that balanced the potential risks, but unfortunately neither of these is the case. There is abundant and robust evidence that raw meat poses a greater risk for infectious disease and parasites than cooked meat, both in terms of studies of contamination of raw pet foods (1,2,3,4,5,6) and the overwhelming evidence in humans that handling and eating raw meat increases these risks and cooking reduces them. It is simply a fact that raw meat is more dangerous than cooked meat, and there is no good argument or evidence that this is not true for pets as it is for people.
A more complex attempt to dismiss the APN findings, and one which is getting some attention online, comes from a raw feeding advocate (and perhaps not surprisingly a marketer of raw foods and other alternative health products), Dr. Conor Brady.
Dr. Brady has a PhD in animal behavior and states that is research focus involved nutrition, so one would expect him to at least present a scientifically reasonable argument. Any study has limitations, and the Australian APN study is no exception, so a science-based critique would be a normal and welcome part of the scientific process.
Sadly, this is not what Dr. Brady offers. Instead, he lurches from scientifically sloppy arguments to cherry-picking of evidence to empty ad hominem attacks on the pet food industry. What he fails to do is provide any real reason to doubt the findings of the APN study.
What Does the Australian Study Actually Say?
Let’s start by looking at what the APN study actually says. The core of the argument made in the study is this:
- Up to 40% of Guillain-Barre Syndrome (GBS) cases in humans may be triggered by the bacterium Campylobacter.
- Most Campylobacter infections in humans come from eating or handling raw poultry.
- APN is believed to be a canine version of GBS, so the study sought to see whether there was an association between APN, Campylobacter, and eating raw chicken.
- APN did turn out to be associated with Campylobacter. 48% of dogs with APN had this bacterium while only 23% of healthy digs did. When looking at recent Campylobacter infections, which would be the most likely to serve as a trigger for autoimmune diseases like APN, three times as many APN dogs had it compared with control dogs.
- APN was also associated with feeding raw chicken. 96% of APN dogs were fed raw chicken while only 26% of control dogs were. Only 1 APN case was not fed raw chicken, and this dog had daily contact with live poultry.
Give these clear associations, it is likely that Campylobacter acquired from raw chicken is a trigger for some APN cases, as it is a trigger for GBS in humans. There are likely other triggers as well, but in this population of dogs feeding raw chicken seems a clear risk factor which would be easily eliminated. If there were clear and proven benefits to feeding raw chicken that outweighed this risk, it might still make sense to do so, but no such benefits have ever been demonstrated.
Dr. Brady’s Attempted Rebuttal
So now let’s turn to Dr. Brady’s comments on this study. He begins reasonably enough by acknowledging that Campylobacter is a serious infectious organism and that raw chicken is a common source for it:
Raw chicken is certainly a source of Campylobacter and a lot of raw dog foods are based on raw chicken. What’s more, Campylobacter is well known to put you on your ass, or at least pooing a lot out of it. It is the most common bacterial cause of enteric disease worldwide, with two million American cases reported annually.
From there, though, he goes through a series of objections which range from reasonable but misleading to completely ridiculous. Let’s take each in turn.
- Do most dogs have Campylobacter in their intestines regardless of what they are fed?
The prevalence of Campylobcater in healthy dogs varies. Some studies show rates from 25-58%, as Dr. Brady claims, but others show much lower rates (such as this study in Poland with infection rates < 5%). Dr. Brady is being misleading, however, in suggesting that the rate in the Australian APN study was irrelevant because it was “normal” or the same as in normal dogs in Australia. The only other study looking and Campy in Australian used mostly stray dogs, which obviously have different diets and health status from owned pet dogs.
Certainly, not all dogs with Campylobacter will get sick, and not all varieties of Campylobacter are pathogenic. However, that has little to do with the results of the APN study. The dogs with APN still had Campy at a much higher rate than the dogs without APN, and this difference doesn’t magically go away just because other dogs in other places have had Campylobaxcter without having APN. As Dr. Brady acknowledges, Campylobacter is a potentially serious infection often acquired by exposure to raw chicken, and this remains true even if some strains are worse than others and not all dogs exposed to it get sick.
- There are many potential triggers for GBS and APN.
So what? If Campy from eating raw chicken is a risk factor (potentially causing 40% of human GBS cases), shouldn’t we do what we can to eliminate this and reduce the risk? Dr. Brady’s argument is like saying that because some people die in car crashes from reasons other than not wearing a seatbelt, we can ignore the fact that not wearing a seat belt is a major reason people do die in car wrecks. Medicine and public health are about reducing risk where we can, not creating a risk-free world. Until there is evidence of benefit from feeding raw meat (and right now there isn’t!), doing so despite the risk of diseases like Campy and APN makes no sense.
Dr. Brady makes a number of misleading or false statements in this section of his post. For one, he cites a paper that found no association between APN and Campylobacter to suggest this contradicts the Australian study. What he ignores is the fact that the paper he cites studied an entirely different population of dogs in another part of the world, it used less reliable measures of Campylobacter infection (serology rather than culture and PCR), and none of the dogs in that study were fed raw meat. In implying that this paper undermines the conclusion of the Australian study, Dr. Brady is either being disingenuous or showing a lack of understanding of basic principles in science and epidemiology.
Interestingly, the study he cites here implicated a different pathogen, Toxoplasma, as a potential trigger for APN. Since this parasite is also mostly acquired in humans from eating undercooked meat, this would actually provide another reason to avoid feeding raw meat to dogs. Dr. Brady cherry picks not only the studies he cites but the parts of them he refers to.
Brady also mentions vaccinations as a potential trigger for APN. In doing so, he cites a case report, which is a much lower level of evidence than the Australian case-control study he is dismissing here. He chooses which evidence to accept and which to reject based primarily on what agrees with his beliefs, not objective scientific criteria for the strength of the evidence.
Even more ridiculous is Dr. Brady’s reference to a study he suggest shows that APN can occur in dogs not even being fed “real food” but still nursing (how mother’s milk is not “real food” isn’t made clear). The study he cites, however, is actually a case report of dogs with a protozoal parasite invading their brains and causing neurologic symptoms, which is not even the same disease as the immune-mediated APN in the Australian study. This fast-and-loose approach to scientific evidence is another example of how Brady seeks only to legitimize his existing beliefs with reference to cherry-picked or misconstrued research, not to really listen to the evidence.
- Was the study too small or poorly done?
The short answer is, “No.” Sample size is always an issue in veterinary research, especially when studying uncommon diseases like APN. Most of the time, too small a sample either leads to false negative results due to low statistical power (that is, not finding something that is actually true because you didn’t have enough examples to get a statistically significant result). The other problem with small samples is that random variation between individuals can more easily lead to the appearance of differences between groups that don’t really exist. If you measure the height of five people to determine the average height in the entire country, a sample that includes only men or only NBA basketball players is likely to give you a result that doesn’t accurately reflect the whole population.
A larger sample would certainly strengthen the results of the APN study, but the results were quite consistent and distinctive even with the numbers used. The results were also consistent with the existing evidence regarding the link between Campy and eating raw chicken as well as the link between Campy and GBS in humans. To borrow a phrase from Dr. Brady, it is “extremely unlikely” that the results of this study are due to chance effects from a small sample population.
His second criticism is less reasonable and betrays a surprising lack of understanding of research methods for someone with a PhD. He complains that the control group was not selected “randomly.” He is correct that it was not, but he is confusing this study, which was a case-control study, with a randomized clinical trial, which is a very different design with different methods.
In a case control study, you start by collecting patients with the disease you are interested in. This is commonly done for rare diseases because simply studying a bunch of patients at random would likely never give you enough cases to learn anything from. Once you have your cases, you select controls that are matched to your cases so that they are likely to be representative of the same group that the cases came from. That means deliberately looking for patients with similarities to the patients with the disease such as age, sex, race, etc. This is not a mistake, it is a core feature of the type of study being done.
Dr. Brady then makes a bunch of comments about how the case selection method invalidates the results which illustrate that he doesn’t understand very well the research methods he is critiquing. He complains that selecting staff pets means they aren’t comparable to the APN dogs because they were less likely to be fed raw chicken. However, the fact that dogs without APN are less likely to be fed raw than dogs who are eating raw meat is exactly the thing being studied. If the control dogs and the APN dogs were all eating raw, there would be no way to tell if this was a risk factor or not!
Similarly, Brady complains that the dogs were not matched on weight, implying again this invalidates the results. But once again, this was a deliberate part of the design to allow the investigation of weight as a potential risk factor, as is actually explained in the published study report: “Very coarse frequency matching by dog size (so that this variable could still later be analyzed for associations with case-control status).” It turned out that weight wasn’t a risk factor associated with APN anyway, but breed size category was. Small breeds were more likely to be APN cases that larger breeds.
Now, the authors hypothesized this might be because small breeds were more likely to be fed raw chicken and get Campylobacter, which are the main risk factors associated with APN in this study. Dr. Brady seems to agree that small breeds are more likely to be fed raw chicken, but he makes the odd conclusion that instead of this leading to Campy infection which triggers APN, small dogs are more likely to get APN for some other reason and the fact they eat raw chicken more often is unrelated.
If this is true, then of course we have to ignore all the evidence of association between Campy and GBS and between raw chicken and Campy and just assume there is some other reason small breed dogs get more APN. This is not supported by any reasoning or evidence. It is ultimately just a guess intended to deflect any potential acknowledgement of the risks of raw feeding.
4. Couldn’t Campy in APN dogs be due to something else? Anything else?! ANYTHING BUT RAW!!
At this point, Dr. Brady loses even basic coherence in his argument. He asks the rhetorical question “Might there be another reason dogs with APN shed Campylobacter” and proceeds to admit he doesn’t know, but he is willing to speculate wildly so long as the reason is anything but feeding raw meat. All the evidence that eating raw meat is associated with Campy in humans and other animals is ignored as he grasps at straws to find another answer more compatible with his faith in raw feeding.
He meanders into unsubstantiated musings about reverse causality, suggesting APN weakens the immune system which leads to Campy infection. This is clearly nonsense since APN is an inappropriate immune system reaction, not a weakened immune system, and the overwhelming majority of Campy is associated with eating raw meat in people and dogs without APN.
Brady then launches into a tirade about the evil of feeding dogs carbohydrates that has absolutely nothing to due with Campy, APN, and the Australian study. This is simply hand-waving to distract from the lack of a coherent explanation for the study findings. He also turns the lack of evidence for raw feeding on its head, suggesting that the lack of any research evidence showing health benefits to feeding raw rather than conventional diets is actually a reason to choose raw diets. Talk about smoke and mirrors! The decades of research on conventional diets is casually dismissed by reference to “industry,” which is not only silly but hypocritical for someone who makes his living selling unproven supplements, diets, and dietary advice.
Finally, he launches into a lofty rhetorical assault on the pet food industry, full of sound and fury but also full of bullshit and woefully lacking in facts. Here is a brief sample:
Lacking any evidence to support the use of their junk food products over fresh ingredients, all they have left to convince you to hand over €5 per kilo for what is Weetabix with cows toenail and crushed centrum tablet in it, is smoke and mirrors. And the best smoke is fear. Fear you will do it wrong. Fear they will get sick. Fear you will get sick. Fear your kids will get sick.
…as cereal-based dry food sales stutter and fall worldwide, to be replaced by more natural, raw dog food products not yet owned by them, the multi-billion industry is not going to go down without a fight. The notion of fear and danger will keep coming up, more and more in the future. ..while raw dog food is yet to kill a dog or harm a single human, dry food cannot say the same in either instance. Injury aside, dry foods’ body count from chemical and microbiological contamination is absolutely shocking.
There isn’t a dry-versus-raw debate guys, any more than there is a global warming debate. There is only skewed, industry nonsense and everyone else. Fear is their weapon. Truth is their enemy. The really scary bit is that what is true and what is industry-nonsense will become harder and harder to detect.
Actually, I find the really scary bit to be the ability of a smart, scientifically educated person like Dr. Brady to ignore and distort evidence to preserve his beliefs at any cost. One can speculate on the financial motives that might influence his thinking, as he clearly believes it influences the thinking of anyone who dares to disagree with him, but I actually doubt that’s a major factor. I think he is simply a true believer who fancies himself a brave warrior against the Evil Empire and is unable to accept any facts that might undermine that belief. The real scary bit is that people might belief the rhetoric and the distortions and suffer for it. Despite his bold claim to the contrary, raw food can harm your pets and you and, yes, your children. Here is just one recent example:
The Minnesota Department of Health reports that two children in a single household were exposed to contaminated Raws for Paws product, which was used to feed the family dog. One child’s illness resulted in septicemia (blood infection) and osteomyelitis, a painful and serious bone infection.
Testing performed by the Minnesota Department of Health and the Minnesota Department of Agriculture demonstrated that the same strain of S. Reading found in the ill children was also found in four samples of Raws for Paws Ground Turkey Food for Pets that was used to feed the family pet.
Dr. Brady can call me a dupe or lackey of Big Pet Food if he wants (and I suspect he will). The truth is, I am open to the idea that fresh food, even raw food, might have health benefits. However, the evidence is clear that raw has risks, and it is up to the proponents of raw diets to prove there are benefits that make these risks worth taking. Not with anecdotes, faulty logic about what is “natural,” rhetorical assaults on the pet food industry, or mere passion. They should prove it with data, with reliable evidence derived from appropriate scientific research. Until they do so, there is no reason for pet owners to take the risks they deny exist for ourselves, our pets, or our families.