Microbiome and Diet: A Close Connection Between Humans and Dogs That Extends Even to the Gut

A study published in *Microbiome* shows that the closeness between dogs and humans extends beyond social relationships and is also reflected in the composition of gut bacterial populations. While numerous studies highlight the impact of these microbes on our health (immunity, chronic inflammatory bowel disease, cancer, obesity, brain function, etc.), the close relationship between these two species could have implications for both.   The first finding of this new study is that the microorganisms present in dogs’ intestines are more similar to those found in humans than to those in pigs or mice (63% of the canine microbiota can be mapped to the human microbiota, compared to only 33% in pigs and 20% in mice). This is all the more surprising given that the immune system most similar to that of humans—which is influenced by the gut microbiome—is believed to be that of the pig, an omnivorous animal. First implication: the dog thus becomes a model of choice in the study of human nutrition, a fact not currently taken into account by research. However, while the two microbiomes are similar, they contain different strains specific to each host. Second, this study shows that the composition of the canine microbiome is also strongly influenced by diet. To this end, 32 Beagles and 32 Labrador Retrievers were classified according to their weight (normal to obese). After four weeks on an identical diet, two new groups were randomly assigned: one was placed on a high-protein, low-carbohydrate diet, and the other on a low-protein, high-carbohydrate diet. After another four weeks, the scientists analyzed the dogs’ gut microbiotas. It appears that dogs with normal or even below-normal body weight did not experience any changes in their microbiota between the two four-week periods. In contrast, the situation was different for overweight dogs, regardless of the animals’ breed or sex. These bacterial changes thus allow for a comparison between the gut flora of a healthy individual and that of one in a state of biological imbalance due to a poor diet. It remains to be understood how such a long-standing relationship in the history of domestication has led to such similar microbiomes in species that nevertheless exhibit some major differences in dietary function. For now, the canine model appears to be the most predictive of what we might observe in the human microbiome.