The Two Best Foods for a Healthy Gut

In 2017, a team of university researchers published a study that revealed how different types of diets affect the gut bacteria (microbiome) of dogs.1 The objective of the 28-day study was to determine fecal microbiota and metabolite concentrations in eight adult dogs fed four different diets, including:

  • Two lightly cooked Freshpet diets
  • One raw Freshpet diet
  • One extruded diet (Purina Dog Chow)

The study results showed that (unsurprisingly) there are differences in gut bacteria depending on what food dogs eat, but beyond that, nothing unexpected or out of the ordinary came to light.

Mildly Cooked and Raw Diets Proved More Digestible

One of the study co-authors, Kelly Swanson, a professor of animal and nutritional sciences at the University of Illinois, told PetfoodIndustry.com the food dogs eat has a significant effect on the types of microorganisms found in their digestive tracts.

“The quality and chemical composition of the ingredients and nutrient digestibility are key factors,” says Swanson.

“That is an important factor in our study because the ingredient list, chemical composition (nutrient profile), and nutrient digestibility was quite different among diets. The mildly cooked and raw diets were generally higher in protein and/or fat and were more digestible than the extruded diet.”2

Based on this feedback, the lightly cooked and raw diets performed as I would expect them to, in that they were easier for the dogs to digest than the ultraprocessed extruded diet. If this was a surprise to the researchers, it really shouldn’t have been. And PetfoodIndustry.com made this observation:

“… despite having a higher fat content than extruded dog food, both lightly cooked and raw diets seemed to reduce blood triglyceride concentration, which would be considered beneficial long term. The biological reason for this is unknown.”

My guess is the lightly cooked and raw diets have less unwanted advanced lipoxidation end products3 than the Purina Dog Chow (one of the lowest quality, grain-based kibbles on the market), thus the decrease in the dogs’ blood triglyceride values.

There Is No Equivalency Between Fresh and Extruded Diets

After reading the study and the related PetfoodIndustry.com article, I was left wondering what the real purpose of the research was. However, one of the final paragraphs of the PetfoodIndustry.com article may offer a hint:

“Since all three types of dog food didn’t seem to result in health problems, one takeaway from this research may be that extruded, lightly cooked and raw dog foods can all meet dogs’ nutritional needs if made using evidence-based guidelines and safety protocols.”

There it is again, that strange reference to no health problems in the dogs who ate the four pet foods for 28 days. Perhaps the hoped-for outcome was that the dogs wouldn’t do as well on the fresh or raw diets. Or perhaps it was an attempt to establish that fresh and processed dog foods are the same.

Whatever the intent of the research, I’m happy these types of studies are beginning to take place here in the U.S. I feel the pet food industry has no choice but to begin evaluating the health benefits of fresh (raw and gently cooked) pet foods because of their popularity.

While I have some questions about the quality of raw materials used in FreshPet (it’s made with “feed grade” materials and has an exceptionally long shelf life), I’m also perplexed as to how their meat products can remain refrigerated for months without spoiling, when the USDA tells us to consume cooked, refrigerated meat in less than a week.

And while I’m thankful the company can afford to do basic nutritional testing, compared to kibble, I recommend pet parents investigate the dozens of gently cooked pet food brands using human grade ingredients.

I was fortunate to be able to visit Dr. Anna Hielm-Björkman, professor at the veterinary school in Helsinki, Finland, who is also studying dog metabolomics. The DOGRISK program, conducted at the school, is involved in several innovative research programs evaluating the effects of different types of dog foods on canine health. 

Björkman’s findings support the results of this study — raw food is less metabolically stressful than kibble, and raw fed dogs have lower levels of inflammatory and disease markers compared to kibble fed dogs.

The nonprofit Companion Animal Nutrition and Wellness Institute (CANWI) has also completed research comparing the levels of unwanted advanced glycation end products (AGEs) in different types of pet foods. Their studies show raw pet food contains the least amount of these unwanted chemical tagalongs, compared to air dried, canned and kibble pet food.

I find many nutritionists end up with tunnel vision when evaluating and formulating diets. They see food as single ingredients on paper, with pet food recipes viewed solely as chemical compositions with specific various nutrient profiles for many in the pet food industry.

Thankfully, more and more scientists are realizing the “entourage effect” with whole foods is very real; the interactions and benefits of the diverse bioactive compounds found in each unadulterated food that haven’t yet been fully quantified. Their powerful effects on the body aren’t dosed on a milligram per kilogram basis, and they can’t be added to a nutrition spreadsheet, but play mightily into health and healing.

Nowadays, pet food ingredients come as single, highly refined, fractionated ingredients. Parts of fresh herbs, fruits and vegetables are often stripped down to fiber or concentrated into extracts and are significantly different than the fresh, whole foods they started from. Annoyingly, fresh blueberries and blueberry powder both show up on pet food labels as “blueberries.”

So, I disagree with the suggestion by Swanson and colleagues that it doesn’t matter whether dogs are fed fresh food or kibble, since presumably, both types of diets meet their nutritional needs on a spreadsheet. It has been my experience over several decades as a practicing veterinarian and that of many other food-focused vets, that the type of food we offer our animal companions matters very much to their long-term health and well-being.

Fact: Raw Fed Dogs Have Healthier Guts Than Kibble Fed Dogs

Other research on how diet impacts the canine gut microbiome has provided better insight into the benefits of feeding species-specific diets to dogs. For example, a 2016 Italian study compared the influence of a raw meat and vegetable diet vs. an extruded diet.

The study authors concluded that feeding a raw diet “… promoted a more balanced growth of bacterial communities and a positive change in the readouts of healthy gut functions in comparison to [an extruded] diet.”4

In another New Zealand study, the researchers discovered that the dogs fed a raw red meat diet showed higher levels of digestibility of protein and energy than dogs fed kibble. They also produced less poop with lower levels of fecal volatile fatty acids.5 As for gut bacteria, the study authors noted that:

“Diet significantly affected 27 microbial families and 53 genera in the faeces. In particular, the abundances of Bacteriodes, Prevotella, Peptostreptococcus and Faecalibacterium were lower in dogs fed the meat diet, whereas Fusobacterium, Lactobacillus and Clostridium were all more abundant.”

The shift in the microbiota correlates to protein and fat digestibility in the dogs. By understanding the relationship between a dog’s microbiome and digestibility of the food consumed, we gain insight into the influence of diet on the overall well-being of pets.

Fresh Food Is the Best Food for Pets

For the record, I’m not endorsing the Freshpet brand of dog foods. But as my regular Healthy Pets visitors know, I’m most definitely an advocate of feeding pets fresh food, preferably human grade — but honestly, any brand of nutritionally balanced fresh food — over biologically inappropriate dry food.

I recommend transitioning your pet away from “fast food” (kibble), and instead feeding a nutritionally optimal, species-specific diet, which means food containing unadulterated (less processed), high-quality animal protein, moisture, healthy fats and fiber, with low to no starch content.

A nutritionally balanced raw or gently cooked homemade diet is the top choice for pets, but only for those pet parents who are committed to doing it right. If you don’t want to deal with balancing diets at home, feeding a pre-balanced, commercially available raw or gently cooked food is a good alternative.

And be sure to incorporate a variety of fresh foods into your pet’s diet, too. Adding fresh foods from your refrigerator to any meal can provide your furry family member with a variety of polyphenols, antioxidants, enzymes, and bioactive substances that nourish your pet’s microbiome and immune system.

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