Are Grains Bad for Your Dog? The Science Behind Canine Evolution and High-Starch Diets

Claire Lucie Sonck
Mar 14
7 min read

Updated: Mar 21

The Evolution of Dogs: From Wolves to Starch-Digesting Omnivores

Dogs share a common ancestor with wolves, but they are not the same species. Genetic studies show that dogs and wolves split into separate species between 27,000 and 40,000 years ago, leading to distinct differences in DNA, behavior, and dietary needs. This means that while they share some traits, dogs have evolved their own unique nutritional requirements over tens of thousands of years.

''A key study published in Nature (Axelsson et al., 2013) revealed that domesticated dogs have multiple copies of the AMY2B gene, which is responsible for producing amylase, the enzyme that breaks down starch. While wolves typically have only two copies of this gene, domestic dogs have develop up to 30 copies of that genes, the same as humans, making them able to thrive on high-starch and humans diet.''

This genetic adaptation coincided with the rise of agriculture, as early dogs scavenged human settlements for food scraps, including grains. Whole grains have been a primary ingredient in the canine diet for at least 10,000 years, dating back to the Neolithic period, when humans first began cultivating crops. Over generations, dogs that could efficiently digest starch had a survival advantage, passing on these genes to their offspring.

Scientific evidence suggests that it takes between 3,000 and 4,000 years for a species to adapt to a new diet at a genetic level. Since grains have been a core part of the canine diet for over 10,000 years, they are not only safe but a natural and beneficial source of nutrition for modern dogs. This evolutionary shift proves that dogs are not strict carnivores like their wolf ancestors, but rather omnivorous animals that thrive on a varied diet—including grains.

The Role of Whole Grains in Canine Nutrition

Whole grains have been a primary source of nutrition for dogs for thousands of years, from farm dogs eating barley and oats to sled dogs thriving on rice-based diets. Despite modern misconceptions, whole grains provide essential nutrients, including:

Complex carbohydrates for sustained energy
Dietary fiber to support digestive health
B vitamins for metabolism and cell function
High-quality plant-based protein – Contributes to a well-rounded amino acid profile.
Essential minerals like magnesium, iron, and zinc
Antioxidants that support immune health

Unlike highly processed grains, whole grains retain their fiber and nutrient content, making them a valuable component of a balanced canine diet. Dogs digest cooked whole grains very well, and in fact, are commonly easier to process than raw meat for some dogs with sensitive digestion.

However, the problem is not grains themselves but how they are processed. Minimally processed whole grains such as brown rice, oats, quinoa, and barley are extremely healthy for dogs.

On the other hand, ultra-processed grains, like those found in most commercial kibble, have been stripped of their nutrients and fiber, leaving behind a starchy filler that can contribute to metabolic dysfunction, inflammation, and disease. Studies have linked the consumption of ultra-processed carbohydrates in pet foods to increased risks of obesity, diabetes, and even cancer (Knueven et al., 2015; Larsen et al., 2017).

Debunking the ‘Grain-Free’ Hype: Marketing vs. Science

The popularity of grain-free diets skyrocketed due to marketing claims that grains are unnatural, inflammatory, or linked to allergies. However, there is no scientific evidence to support these claims. Let’s break down some of the most common myths:

1. “Grains cause allergies in dogs”

This is one of the most misleading claims. According to veterinary dermatology studies, the most common food allergens in dogs are animal proteins—specifically beef, chicken, dairy, and lamb—not grains (Mueller et al., 2016). While some dogs may be sensitive to specific grains, true grain allergies are extremely rare.

Additionally, dogs and wolves split into separate species between 27,000 and 40,000 years ago, with dogs adapting to a starch-inclusive diet over thousands of generations. Whole grains have been a primary ingredient in the canine diet since at least the Neolithic period (10,000 years ago), meaning their bodies have long been accustomed to digesting and thrive on grains.

2. “Grains cause inflammation and digestive issues”

The real culprits behind inflammation in dog food are ultra-processed ingredients and synthetic additives, not whole grains. In fact, whole grains are an excellent source of prebiotic fiber, which promotes gut health by feeding beneficial bacteria.

Studies have shown that high-heat processing of carbohydrates in kibble can lead to the formation of advanced glycation end products (AGEs), which are linked to oxidative stress, inflammation, and chronic disease—including cancer (de Wilde et al., 2019). This means it’s not the grains themselves, but rather how they are processed, that can lead to health issues.

In fact, studies have shown that whole grains promote a balanced microbiome and lower inflammatory markers like C-reactive protein (CRP), making them a valuable addition to an anti-inflammatory diet.

3. “Dogs are carnivores and don’t need grains”

This claim ignores the evolutionary adaptations that separate dogs from wolves.

Scientific research, including a key Nature (Axelsson et al., 2013) study, reveals that domesticated dogs have multiple copies of the AMY2B gene, which allows them to digest and utilize starch. While wolves typically have only two copies of this gene, domestic dogs can have up to 30 copies of this gene, same as humans, proving they are well-adapted to digesting starch and carbohydrates, including grains.

Additionally, it takes between 3,000 and 4,000 years for a species to adapt to a new diet at a genetic level, and whole grains have been a staple in canine diets for at least 10,000 years. This means that dogs are omnivores, not facultative carnivores like wolves.

4. “Grain-free diets are healthier”

Not only is there no scientific basis for this claim, but studies suggest that grain-free diets may actually be harmful to dogs.

In 2018, the FDA began investigating a rise in cases of dilated cardiomyopathy (DCM) in dogs fed grain-free dietshigh in legumes (lentils, peas, chickpeas) instead of grains. While initial concerns suggested a link between grain-free diets and heart disease, no direct causal relationship has been found between whole grains or legumes and DCM.

Further investigations concluded that the real issue is not the ingredients themselves, but rather how pet food is processed. Highly processed pet foods—whether grain-inclusive or grain-free—may contribute to nutritional imbalances and deficiencies, particularly in taurine and other key heart-supporting nutrients. The FDA has since closed its investigation without finding definitive evidence that grain-free diets directly cause DCM.

Rather than avoiding grains or legumes, the focus should be on feeding whole, minimally processed ingredients as part of a fresh, balanced diet that supports long-term canine health.

Conclusion: Should You Feed Your Dog Grains?

The science is clear—grains are not only safe but beneficial for dogs. Evolution has equipped dogs with the ability to digest starch efficiently, and whole grains provide a wealth of essential nutrients. The grain-free trend is largely driven by marketing rather than science, and in some cases, it may even pose risks to canine health.

If you’re choosing grains for your dog, opt for minimally processed whole grains like brown rice, oats, barley, or quinoa, which provide valuable fiber, vitamins, and minerals. Avoid heavily processed grain fillers found in low-quality kibble.

At the end of the day, a well-balanced diet tailored to your dog’s individual needs is what truly matters—and for most dogs, that includes grains.

What are your thoughts on grains in dog food? Have you noticed a difference in your dog's health with or without grains? Let’s start a discussion in the comments below!

Scientific Evidence Supporting Grains in Dog Diets

A growing body of research supports the role of grains in dog diets:

Dogs digest starch efficiently: Axelsson et al. (2013) showed that domesticated dogs have evolved multiple copies of the AMY2B gene to digest starch.
Whole grains provide essential nutrients: Studies have demonstrated that grains contribute to a well-balanced diet for dogs, improving digestive health and reducing the risk of certain diseases (Zentek et al., 2004).
Grain-free diets and DCM: A 2018 FDA report highlighted concerns about grain-free diets potentially contributing to heart disease in dogs due to taurine deficiencies and nutritional imbalances.
Ultra-processed grains and chronic disease: Research has shown that the high-heat processing of grains in kibble contributes to the formation of AGEs, which are linked to chronic inflammation, metabolic disorders, and cancer in both humans and animals (de Wilde et al., 2019).
Dogs digest starch efficiently: Axelsson et al. (2013) found that domesticated dogs have evolved multiple copies of the AMY2B gene, which allows them to digest starch more efficiently than wolves. (Axelsson et al., 2013, Nature)
Whole grains provide essential nutrients: Studies show that whole grains contribute to a balanced diet, supporting digestive health, gut microbiota, and metabolic function in dogs. (Zentek et al., 2004, Journal of Animal Physiology and Animal Nutrition)
The evolutionary adaptation to a starch-rich diet: Genetic research indicates that dogs have been consuming grains for at least 10,000 years, with evolutionary adaptations supporting starch digestion. (Freedman et al., 2014, PLoS Genetics)
Grain-free diets and DCM: The FDA investigated a rise in cases of dilated cardiomyopathy (DCM) in dogs on grain-free diets and found concerns related to nutritional imbalances, particularly taurine deficiencies. (FDA Report, 2018)
No proven link between whole grains and DCM: Research has not found a direct causal link between whole grains or legumes and heart disease in dogs. Instead, processing methods and overall dietary formulation appear to play a larger role. (Kaplan et al., 2022, Journal of Animal Science)
Ultra-processed grains and chronic disease: Studies show that high-heat processing in kibble leads to the formation of advanced glycation end products (AGEs), which are linked to oxidative stress, inflammation, and chronic disease, including cancer. (de Wilde et al., 2019, Journal of Nutrition)
Whole grains and anti-inflammatory properties: Research suggests that whole grains contribute to a balanced gut microbiome and lower inflammatory markers like C-reactive protein (CRP), supporting immune health. (Montoya et al., 2020, Frontiers in Immunology)
Historical evidence of grain consumption in canine diets: Archaeological findings suggest that early domesticated dogs consumed starch-rich diets as they coexisted with human agricultural communities for thousands of years. (Perri et al., 2021, Scientific Reports)

By looking at real-world evidence, we also see that many long-lived dogs have been fed diets rich in minimally processed whole grains, further debunking the myth that grains are harmful.

Disclaimer:

This article is for informational and educational purposes only. It is not intended to replace professional veterinary advice, diagnosis, or treatment. Always consult with a qualified veterinarian or canine nutritionist before making changes to your dog’s diet, health routine, or medical care. The author is a certified canine nutritionist and does not claim to diagnose or treat medical conditions.

No part of this article may be reproduced or distributed without written permission from the author.