LINKING A TOXIC GLUCOSE METABOLITE TO GLYCEMIC AND CARDIOVASCULAR RESPONSES IN AN OMNIVORE COMPARED TO A CARNIVORE
Pet nutrition is becoming increasingly important to pet owners with more owners claiming that they are conscious of the ingredients in their pet foods. Healthy whole nutritious pet foods are important to pet owners although some of the health claims made by pet food companies do not have a scientific basis. High protein costs are a common driver for the pet food industry to formulate their foods with increased levels of carbohydrates. Cats have different nutritional requirements, and being a carnivorous species, are thought to handle high levels of ingested carbohydrates poorly. The purpose of this thesis was to determine how glycemic index values differed for various starches and diets in a carnivorous species, cats, and an omnivorous species, dogs. With this novel information, low glycemic index diets were formulated using either modified cornstarch or pulse starches (pea, lentil or faba bean) as carbohydrate sources. I aimed to provide long-term health benefits to dogs and cats through feeding low glycemic index diets that would control postprandial glycemic and insulinemic responses, plus reduce postprandial levels of the toxic glucose metabolite, methylglyoxal, and promote cardiovascular health. Two studies were designed to determine the research objectives: • Determine species metabolic differences (dog versus cat) to both low and high glycemic index carbohydrate sources, and link these to postprandial cardiovascular and methylglyoxal results; and • Compare long-term health benefits of diets formulated with pulse starch to a modified cornstarch diet in dogs versus cats, including digestibility, glycemic, insulinemic, and cardiovascular responses, and postprandial methylglyoxal levels. For the first study the glycemic index was determined for nine different starch sources and four whole formulated diets in laboratory beagles and domestic, mixed breed cats. For this first study, I related the postprandial glycemic and insulinemic responses to methylglyoxal and cardiovascular responses after single feedings in animals not previously acclimated to the test diets. The results from this study showed that pulse starches produce lower GI values in both dogs and cats when compared to common pet food ingredients such as unmodified corn, rice flour and white wheat flour, and other starch sources such as tapioca, modified cornstarch, and potato. However, in dogs only, the potato starch produced the lowest GI value. When modified cornstarch versus pulse starches (pea, lentil or faba bean) were used at a 30% inclusion rate in whole diets, glycemic responses increased in both species, likely due to formulation and processing effects. Contradictory to what was initially thought, cats can handle higher amounts of carbohydrates in their diets which is shown by the low glycemic responses and high digestibility of the pure starches and whole diets. Postprandial increases in plasma glucose were linked with increased levels of methylglyoxal in dogs. In contrast, in cats, there was no association between glycemic index and postprandial methylglyoxal changes. Interestingly methylglyoxal decreases from pre-feeding to 60 minutes postprandial were observed for most of the starches and whole diets. Contradictory to the acute study, the long-term study results showed that this link between postprandial glycemic response and methylglyoxal is not supported in dogs. The long-term study results in the cats agree with the acute study in that there was no link between postprandial methylglyoxal levels and glycemic index. The results from this study support the use of low glycemic pulse carbohydrate sources in pet food, which can now be marketed as low glycemic index food using scientific support. I also showed that cats are able to control postprandial blood glucose levels following consumption of multiple starch sources, contradictory to what has been previously reported in the literature.
Carbohydrates, Glycemic Index, Methylglyoxal
Master of Science (M.Sc.)