Dog Allergies + Evaluating Scientific Evidence
Edith broke a nail earlier this week (her dewclaw). It’s a very minor injury and she is fine. Though, if you saw her without context you’d think she broke her leg based on the size of her bandage. She’s already been getting special treats to help her heal. :)
Are Cedric and Edith allergic to anything? So far, neither of them have shown any symptoms of food allergies.
A while back, Cedric had peanut butter for the first time (it was way too big a serving looking back) and had diarrhea shortly after. He’s had peanut butter several times since without any issues. He just had it in much smaller amounts. This is an example of food intolerance. If he were allergic, any amount would trigger a series of symptoms.
If your dog can’t have dairy is it an allergy or just lactose intolerance?
Often allergies, food intolerance and even toxicity are confused to be the same thing. The TLDR of this week’s newsletter is that dogs are probably not as allergic to foods as you think.
We’ll start with a short primer on how to interpret scientific data.
Before that here are this weeks recipes.
How to assess scientific research
You are on your own when it comes to research. If you don’t know how to evaluate information, you’re going to end up believing a lot of things that are based off of bad science. Unfortunately even articles that look credible (think from the AKC, Pet MD, vet clinic sites, etc) tend to cite no or very low quality sources.
Scientific evidence has varying levels of reliability. The above pyramid shows how scientists regard the reliability of a given paper. Randomized controlled trials (RCTs) are where scientists test an intervention like a drug and measure a specific outcome against a control (sometimes called placebo, a pill that does nothing). The best evidence comes from comparing multiple RCTs, these are often called a meta-analyses, and it’s why they are at the top of the pyramid. The lower down the pyramid you go the lower the quality of evidence.
Everything from cohort studies on down is indirectly studying something that happens. For example let’s say we want to find out if people who eat fish live longer than those who don’t. There’s no way for us to test that long-term, so we have look at the natural population and ask them. These kinds of studies usually involve surveys, either self reported or researchers observing subjects’ habits. When people self report they can forget exactly what they ate or how much. A researcher observing something can also make mistakes. This is why it’s generally considered to be less reliable than a controlled study.
It gets worse. Much of the research published in recent years is not reproducible. Many scientists believe there is a reproducibility crisis. Reproducibility means that when scientists run the same experiment more than once, they get the same result. When research can’t be reproduced, it’s unlikely to be true.
So even randomized controlled studies, which are near the top of the above pyramid, can be misleading unless it’s reproducible. Near the bottom of scientific evidence is expert opinion. In other words, the scientific community does not regard the opinions of experts as high quality evidence, and neither should you (let alone someone on the internet). Remember almost anyone can write a paper and publish it.
Although meta-analyses are regarded as the highest quality scientific evidence because they attempt to show reproducibility, meta-analyses can still be wrong. Researchers must choose which studies to include and which studies to omit and that process can introduce bias, both intentional and accidental.
So what are we supposed to do? First, we all have to learn how to interpret scientific data so that people can’t use “science” to trick us (which is the goal of this post). Second, we have to understand who funds the research. Many special interest groups fund studies to support their commercial interests. Big food has been doing this for decades. This is why we often cite Waltham research (owned by Mars) when it contradicts Mars’ commercial interests. Third, we all have to hold on to conclusions very loosely as things are constantly evolving. Fourth, we have to continually update our knowledge base.
Allergies and food intolerance in dogs
A lot of dogs have issues with food, but there are different kinds of issues. Allergies are defined as immune responses when an animal’s immune system mistakes a protein (usually) in food, the air, or surfaces as a pathogen (like bacteria, viruses and fungi). This is different than a food intolerance where animals have difficulty digesting a food. Intolerance can be caused by lacking enzymes to digest certain nutrients (such as lactose intolerance). Another type of intolerance is caused by the animal being unable to absorb the nutrient (such as fructose intolerance).
This 2002 study suggests that food intolerance is more common than food allergies in dogs. Similar claims are made about people, and this is significant because management of allergies and intolerances are fundamentally different. People and dogs with allergies often must avoid the offending allergen (the exception is immunotherapy for allergies which is effective to desensitize animals when they are young), while intolerance usually means that small amounts of the offending foods can be consumed. The symptoms are also different, with allergies often causing systemic issues like rashes, difficulty swallowing and wheezing. Food intolerance is more commonly associated with digestive issues, though systemic issues can also occur at high doses.
The most accurate way to confirm allergies is through skin tests where allergens are poked into the skin and the reaction is measured. We were quite surprised to find that there is little consensus on the actual prevalence of food allergies in dogs. See literature review here. Some sources place the incident of food intolerance at approximately 17% while Banfield pet hospitals claims only 0.2% of dogs are truly allergic to foods. However, another prospective study following 90 West Highland Terriers for three years found that 52% showed clinical symptoms of food allergies while 17% were confirmed to have food allergies.
Tufts University claims that only about 10% of cases where owners suspect food allergies are actually food allergies. Their expert opinion is that most of the skin allergies that dogs have are related to environmental allergens and that most reactions to food are food intolerance to some ingredient in used in the kibble. But because they have few citations here I’m skeptical.
So what does all this mean for my dog’s allergies?
The good news: based on the literature, if you think your dog has food allergies, there is a good chance (better than 50%) that it’s not.
The bad news: there is a number of other things that it could be, from allergies to dust mites, pollen, mold and other allergens or it could be food intolerance.
What to do about food intolerance?
In general we keep our dogs’ diet simple and whole-food based. Modern dog foods contain all sorts of animal byproducts, isolates, processed carbohydrates and chemicals that can amplify issues. On top of that many items, not listed in ingredients, make their way into pet foods.
Another strategy to find offending foods is elimination diets. This process involves feeding only 2-3 foods for extended periods allowing your pet to recover from allergy symptoms. Once they are symptom-free, new foods are introduced one by one to identify the foods that are causing issues. This is a slow and painful process, but may be worth it to help improve your dog’s life in the long run. Here’s an intro to elimination diets for dogs from Tufts University.
That’s all for this time!
Hope you’re all having the best week,
Joelle and the Precious Creatures Team