This week on the Cone… Dr. Andy Roark talks to the Skept Vet himself, Dr. Brennan McKenzie about a topic that seems to get blood boiling among veterinarians, vet nutritionists, pet owners, breeders and dog food manufacturers. Why are we divided about grain-free pet foods, and what does the research really say?

dog eating grain-free kibble at veterinary hospital


  • Grain-Free diets weren’t largely prevalent before the 2000s.
  • Although evidence is unclear, grain-free was promoted as an option to help with skin allergies and G.I. disease.
  • Gluten phobia in human medicine contributed to concerns in animal medicine.
  • In 2019 approximately 43% of diets sold are grain-free, compare that to 15 years earlier where grain-free accounted for roughly 2% of diets.
  • In 2018 the FDA starting seeing an increased report of dilated cardiomyopathy in dogs. In a little over a year, they went from seeing 1-2 reported cases to over 1,100.
  • In the 80’s DCM in cats was linked to a nutritional deficiency in Taurine. When cat’s diets were supplemented the issue virtually disappeared.
  • DCM in dogs was understood to be linked to genetics/breed.


  • Correlation does not imply causation.
  • Increased reporting of DCM may be due to increased awareness.
  • There are large commercial implications to both sides of the argument. Diet change can be used in conjunction with other treatments for DCM. Correlation does not imply causation.
  • “Hard to change our perspective on these things when we think we already know the answer.” – Dr. McKenzie


Personal Branding w/Dr. Andy Roark:
Dr. Andy Roark Swag:


Dr. McKenzie has always pursued a wide range of interests both within and outside of science. After completing a bachelor’s degree with majors in English Literature and Biology at the University of California at Santa Cruz, he obtained a Master’s in Physiology and Animal Behavior and worked for several years in environmental and behavioral enrichment for captive primates.

Dr. McKenzie then attended the School of Veterinary Medicine at the University of Pennsylvania and began working as a small animal general practice veterinarian. In addition to his clinical work, he has served as President of the Evidence-Based Veterinary Medicine Association, lectured on evidence-based medicine at numerous veterinary conferences, and published journal articles on such topics as overdiagnosis, cognitive bias in veterinary clinical decision-making, and the philosophical underpinnings of evidence-based and alternative medicine. Since 2009, Dr. McKenzie has managed the SkeptVetBlog and associated social media outlets, including a series of science-based pet health videos on YouTube. He has also been an occasional contributor to the popular Science-based Medicine blog.

While working as a practitioner, speaker and writer, Dr. McKenzie has continued to pursue post-graduate training and completed his MSc in Epidemiology at the London School of Hygiene and Tropical Medicine in 2015. He also teaches veterinary students in his practice as well as undergraduate biology majors, he writes a monthly column on evidence-based medicine for Veterinary Practice News magazine, and he has published a book for pet owners and veterinary professionals — “Placebos for Pets? The Truth About Alternative Medicine in Animals”.

In his sparse free time, Dr. McKenzie enjoys reading, hiking, playing his mandolin and guitar, traveling with his family and sitting on the couch with his dogs watching the hummingbirds and woodpeckers outside his living room window.

Editor: Dustin Bays
@Bays4Bays Twitter/Instagram