Vet's Note: Should Glycemic Index Guide Your Choice of Pet Food?
To this day, research on glycemic index in dogs and cats remains very scarce. Rather than be held hostage by marketing terms, focus on feeding a balanced diet.
The glycemic index (GI) comes from human nutrition. So what exactly is it, and what does it mean for dogs and cats?
Do pets have a glycemic index?
In humans, GI measures the blood-glucose response to a carbohydrate compared with pure glucose. The benefits of a low-GI diet are established in people: lower cholesterol and triglycerides, and reduced risk of obesity, diabetes and cardiovascular disease.
In dogs and cats, however, research is still very limited. Species differences (omnivore vs. carnivore) mean different enzymes and mechanisms, so carbohydrate digestion, absorption and metabolism are not the same. The "low GI" many pet-food brands cite is actually a human value — and GI measured in human diets should not be applied directly to dogs and cats.
GI is also usually a reference value for a single starch, yet cooking method and degree of processing change it (ground raw rice and cooked rice have different GIs). Since pet food blends many ingredients, some question how meaningful ingredient GI is for judging a finished food.
Research on pet GI is still scarce…
A 2020 study fed sled dogs single starches and commercial kibbles and compared glycemic responses using human GI methodology. Blood-glucose and insulin responses to single starches and to kibble were similar, and kibble based on traditional cereal grains produced the slowest insulin peak (so stop maligning grain-inclusive food!). The authors noted, however, that human GI methods may not suit dogs, that individual variation was large, and that more research is needed.
On dog–cat differences, a 2021 study measured post-starch glycemic response, GI, insulin, methylglyoxal (a toxic glucose metabolite) and d-lactate in both species. Peak post-meal glucose was surprisingly similar between dogs and cats, but glucose fell more slowly in cats, reflecting weaker glycolytic enzyme activity. Dogs' overall response resembled humans'; cats' did not. The study concluded the GI concept applies to dogs but not to cats.
Myth-busting: low-GI food does not mean no diabetes
Owners ask whether low-GI food prevents diabetes. Beyond individual assessment, the general advice is a balanced diet. Setting aside the scarcity of research, a low-GI food fed in excess causes obesity — the most common risk factor for diabetes. The first goal for health is maintaining body condition: feel your pet regularly, weigh them, keep them trim. For pets already diagnosed, follow your clinician's instructions: insulin on schedule, appropriate body condition (lose weight if needed), diet discussed with the vet and never changed on a whim — that is what gives them a stable, comfortable life.
References
- Rankovic A, et al. Glycemic response in nonracing sled dogs fed single starch ingredients and commercial extruded dog foods with different carbohydrate sources. J Anim Sci. 2020;98(8).
- Briens JM, et al. Glycemic, insulinemic and methylglyoxal postprandial responses to starches alone or in whole diets in dogs versus cats. Comp Biochem Physiol A. 2021;257.
- Behrend E, et al. 2018 AAHA Diabetes Management Guidelines for Dogs and Cats. J Am Anim Hosp Assoc. 2018;54(1):1-21.
