In the pet food industry, the topic of glycemic index (GI) seems to have come and gone and come again. Glycemic index is a measurement of the blood glucose response to carbohydrates. It is measured specific to a set quantity of individual carbohydrates, compared to the response to pure glucose or white bread.
In human medicine, GI can be affected by a variety of factors pertaining to the individual or the food item itself. Different individuals may have different glycemic responses to the same food and even a single individual could have different responses at different points throughout the day. Insulin response and the ability of the body to regulate blood glucose levels are impacted by medical conditions and even by stress. Different cooking methods and even different levels of “ripeness” of a particular food can change the glycemic response to that food. The combination of carbohydrates with a high GI with fats or fibers can lower the overall GI of the food being consumed. So, GI values applied to foods are general guidelines, but may not be applicable across the population consistently.
GI still is an important tool to guide healthier diet choices, particularly in weight management and diabetes, but it is important to understand its limitations. One example that illustrates this clearly is carrots. Most of us would consider raw carrots to be a healthy snack. The GI of carrots is relatively high, though, which may lead us to cross them from our list. However, an individual would have to consume more than a pound of carrots before there was any undesirable impact on blood glucose levels.
There are several issues of concern surrounding GI as it relates to pet nutrition. First, pets are not people. Humanization of pets has allowed for the explosion of many trends in the industry, with a phenomenal impact on the foods that are purchased. But humanization of pets does not turn the metabolism of a dog or cat into that of a human.
I already mentioned that weight management and diabetes are two situations where GI might be particularly useful. Cats, as obligate carnivores, would not be expected to have the same response to a food or ingredient as a dog, an omnivore. Interestingly, cats can develop Type II diabetes as a result of being overweight, just like humans (omnivores like dogs), but dogs do not. Cats can also develop stress hyperglycemia, even to the point of spilling glucose in their urine.
Science and medicine have a long history of using animal models to test medications or treatments or even poisons. The reverse occurs sometimes as well, and many pharmaceuticals that were developed for human use are used in veterinary medicine. The question of how well the GI values for human foods pertain to pets has not been answered. This is the stance that regulatory officials take on GI claims.
Companies could take on the expense of testing a particular pet food or foods in a group of animals to measure the glycemic response. A large group of subjects under a variety of conditions would be ideal, but costly and time consuming. Whether the data would be acceptable to regulatory officials to allow a claim on a package is an unknown. And as anyone involved in regulatory compliance knows, what one state might allow, another may deny. The Food and Drug Administration does not evaluate glycemic claims as it does for hairball or urinary tract, and there is not an accepted protocol for investigating GI for pet foods that I am aware of at this time.
Another way in which the current GI values do not pertain directly to pet food is the fact that GI measures the response of blood glucose to specific individual ingredients. Pet foods contain a variety of ingredients in varying proportions to create a complete and balanced food. If there can be variability in an individual’s response to different foods based on ripeness and other factors, imagine the magnification of this impact when looking at the response to a complete pet food that is made up of numerous ingredients.
GI of pet foods certainly could provide value in managing the overall health of pets. However, we cannot blindly apply the GI of individual ingredients in a pet food formulation to create a value that has real meaning. Unfortunately, nutritional research for dogs and cats is expensive and time consuming. Information being studied today may not be available for years. There is a lot of research that has been done investigating carbohydrates and fibers and how these nutrients relate to pet nutrition and pet health. Maybe a new, pet-specific GI will evolve from this body of work and offer manufacturers an opportunity to be on the cutting edge of this particular nutritional concept.