Your Dog's Gut Microbes Change Quickly With New Diet

THURSDAY, Aug. 4, 2022 (HealthDay News) -- Switching Fido to a new dog food? What happens in his gut as a result is nothing short of remarkable, a new study reveals.

The population of bacteria living in his gut — his microbiome — will change dramatically in as little as a week.

It starts when "wallflower bacteria," those that were on the sidelines, multiply rapidly to replace the old, the study found. The chemical byproducts of these microorganisms change as they vie for dominance. Many of these byproducts are crucial for your dog’s overall health.

“Metabolites change really quickly, within a couple of days," said study co-author Kelly Swanson, a professor of human nutrition at the University of Illinois, in Urbana. "Bacteria responsively metabolize and deal with the substrates they're given in the new diet. Then it takes a few more days to sort out the microbial pecking order, if you will. Our data show everything stabilizes by day six.”

In mammals, the interaction between nutrients, microbes and their chemical byproducts has long been known, but up until now, scientists have only theorized about the rate of microbial turnover. This new study shows it happens quickly.

“As long as I've been doing animal nutrition research, we’ve argued over how long we need to feed a new diet before collecting samples, when everything's stabilized,” Swanson said in a university news release. “No one has ever tested it definitively.”

For the study, Swanson's team fed the dogs dry kibble for two weeks and then abruptly switched to a new food for 14 days. Half of the dogs ate high-fiber kibble, half consumed a high-fat, high-protein canned diet.

Two days after the diet change, the researchers collected fecal samples. They did so every four days after that. The researchers conducted the process twice and switched dogs to the opposite experimental diet the second time around.

“Oftentimes, we feed a diet and collect the feces, but there's kind of a black box in terms of what’s going on in the gut. We know what some bacterial species metabolize, but definitely a lot of it is unknown,” Swanson said. “Our correlations are the starting point to connect some of the dots, but more targeted research still has to be done.”

The key objective of the study — which was published Aug. 1 in the journal Animal Microbiome — was to monitor microbial changes over time, but it also supported earlier findings that a high-fiber diet is healthier for dogs than one that is high in fat and protein.

These results weren't unexpected, but the researchers were surprised that the two extreme diets reached equilibrium at the same time. Metabolite changes were found for both diets on day two and changes in the bacterial community by day six.

Swanson said the general findings may apply to other mammals' gut bacteria, particularly those of pets and livestock that eat a consistent, controlled diet. For instance, the rate at which the gut microbiome adjusts and stabilizes after a dietary change may be standard for most. And while specific bacterial species and strains may vary among canines, humans and other mammals, metabolite/species correlations may be the same, he said.

While researchers tested an extreme diet change, the results still support veterinarians' customary advice to switch to a new dog food brand gradually.

“People usually suggest moving pets over to a new diet over a seven-day period. Our study suggests the microbes can completely change over in that timeframe,” Swanson said. “When you switch diets, the body has to adjust, but the microbes have to change as well. If they’re not in a happy situation, you end up with loose stools or flatulence. So it’s probably good to do it a bit more gradually at home than we did in the lab.”

This research was conducted in collaboration with the pet food manufacturer NomNomNow, Inc.

“Understanding the microbiome is central to our efforts in improving pet health, and this study brings us another step closer uncovering how the canine gut actually responds to a new diet,” said Ryan Honaker, the company's director of microbiology.

More information

The American Kennel Club has more about changing your dog's diet.

SOURCE: University of Illinois, news release, Aug. 1, 2022