Dogs can quickly feel like part of the family, and a new study shows that our canine pals share more similarities with human beings than we thought - particularly when it comes to gut microbiomes and responses to diet.
By analysing poop samples, both with and without special diets in place, researchers found that the dog microbiome responds in a similar way to the human microbiome – and more so than in other animals like pigs or mice.
Plus, besides adding to the evidence that we share a special bond with our dogs, the study might also help us tackle the growing problem of canine obesity. According to recent figures, more than half of pooches are fatter than they should be.
"These findings suggest that dogs could be a better model for nutrition studies than pigs or mice, " says one of the team, Luis Pedro Coelho from the European Molecular Biology Laboratory.
"We could potentially use data from dogs to study the impact of diet on gut microbiota in humans, and humans could be a good model to study the nutrition of dogs.
"Many people who have pets consider them as part of the family and like humans, dogs have a growing obesity problem. Therefore, it is important to study the implications of different diets."
Stool samples were collected from 32 labrador retrievers and 32 beagles, with an equal number of lean and overweight dogs in the group.
After four weeks of chowing down normal dog food, the animals were split up into two groups for the next four weeks – one was put on a high protein, low carb diet, while the other was given a high carb, low protein diet.
A total of 129 samples were collected at four weeks and at eight weeks, offering up more than a million microbiome genes ready for analysis. These genes were compared against existing catalogues for humans, mice, and pigs.
While the microbes aren't an exact match between humans and dogs, the researchers noted they were "very similar" – closely related strains of the same species.
After the different diets were introduced, the response in the gut bacteria of the dogs to changes in levels of proteins and carbohydrates was similar to the changes scientists would expect to see in humans.
What's more, overweight or obese dogs showed more responsiveness to new diets when it came to the composition of their microbiota – backing up the current thinking that healthy microbiomes are more resilient.
There are all kinds of possibilities opened up by this research: dogs might be better case studies than mice or pigs are for certain types of research on the gut bacteria of humans, and how it relates nutrition, for example.
On top of that, it gives experts a starting point for understanding how changes in diet and microbiome could help tackle the problem of dogs living with excessive weight.
In humans as well, links between the make-up of our guts and our overall health are turning up time and time again.
Considering how early in human history dogs were domesticated - with theories that it may have happened up to 32,000 years ago - it makes sense that our digestive systems have evolved some similarities, especially since we've shared a lot of food resources with them over millennia.
Now that both canines and humans are facing rising levels of obesity, the solutions might also be similar in both cases.
As you might expect, plenty more research is required, to link together the responsiveness of gut bacteria in dogs and humans, and to test these ideas outside the two breeds that have been studied so far.
"Together with the taxonomic census, our study of two dog breeds should provide a baseline for expanding dog microbiome research to other breeds, biogeography, and variation of living conditions," conclude the researchers.
The research has been published in Microbiome.