Many studies investigating human diseases and other health conditions start by looking at how the same or similar conditions work in animals, and how they might be treated or improved.
Some animals encounter the same or extremely similar diseases to those that affect humans, making them viable models for preclinical research.
Moreover, certain animals have similarly structured internal systems — such as the digestive system — which means that they can provide a good approximation of how our own biological mechanisms work.
Therefore, mice and rats are often used to study human diseases, whereas pigs are a favorite go-to model for researching gut health. But now, scientists are looking to another animal that they argue has an even more similar gut microbiome to that of humans: humans' best friend, the dog.
Luis Pedro Coelho — who currently works in the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany — plus colleagues at the EMBL and the Nestlé Purina Research laboratories in St. Louis, MO, hypothesize that dogs may be also be our best friends when it comes to learning more about our own gut health.
However, the same idea applies the other way around, too — if dogs and humans are similar in this respect, perhaps we can apply what we know of managing obesity in humans to our canine companions.
"Dogs are very important in many people's lives and (like us), they increasingly suffer from obesity," Coelho told Medical News Today, explaining why the research team had decided to focus its attention on these animals.
"Thus," he went on, "knowing more about their microbiome and how it is (or is not) affected by diet is an important question."
Their research, the results of which are now published in the journal Microbiome, indicates that dogs' gut microbiomes overlap a lot more with own than those of mice or pigs.
Humans and dogs' surprising similarities
The study — which was co-funded by the Nestlé Purina PetCare Company — was a randomized controlled trial, for which the scientists selected 64 dogs of two breeds: beagle and Labrador retriever.
They worked with an equal number of dogs from each of these breeds, and they also made sure that half of all the canine participants were overweight and that half had a healthy body weight.
Over an initial period of 4 weeks, all of these dogs were fed the same commonly available dog food sold on the market.
Then, the dogs were randomly divided into two groups: one that was to only receive food that was high in protein content and low in carbs, and another that was fed a low-protein, high-carb diet. This stage of the experiment lasted for another 4 weeks.
The researchers collected 129 samples of dog stool, once at the 4-week mark and then again at the end of the study. These samples allowed them to map the gene content of the dogs' microbiomes, identifying 1,247,405 genes in total.
Coelho and team then compared this "gene catalogue" to existing data on the gut microbiomes of mice, pigs, and humans. This allowed them to assess how similar these microbiomes were to each other in terms of their genetic content, plus how the dogs' microbiomes were altered by changing diets.
The team was surprised to find that the microbiomes of dogs were much more similar to the human gut microbiome than those of mice and pigs.
They found a 20 percent overlap between the murine and human gut microbiomes and a 33 percent overlap between our gut microbiomes and those of pigs, but a 63 percent overlap between dogs' gut microbiomes and our own.
"These results suggest that we are more similar to man's best friend than we originally thought," Coelho says.
Still, when speaking to MNT, he warned that these similarities do not mean that we can think of dogs' microbiomes and our own interchangeably.
"[I]t is also important," he explained, "to note that there is significant host-specificity: we share many species [of microbes] with our dogs, but strains are host-specific and human microbiomes are more complex than those of dogs."
'A better model for nutrition studies'?
The scientists also noted that low-carb, high-protein diets and high-carb, low-protein diets influence the gut microbiome in similar ways in the case of both humans and dogs, independently of breed and biological sex.
Overweight dogs responded more strongly to a high-protein diet than their slender counterparts, presenting more drastic changes in the composition of their gut microbiomes.
This sensitivity confirms the existing idea that overweight individuals are more vulnerable to health threats due to the instability of their gut microbiomes.
Looking at the results of their study, the researchers believe that, in the future, humans' best friend may be able to help us gain a better understanding of the mechanisms at play in our own health.
"These findings suggest that dogs could be a better model for nutrition studies than pigs or mice, and we could potentially use data from dogs to study the impact of diet on human gut microbiota."
Luis Pedro Coelho