The Effects of Oral Mannoheptulose Supplementation on Canine Energetics and Macronutrient Utilization

In companion animals there is a growing interest in the use of nutraceuticals for weight management and healthy longevity. A nutraceutical can broadly be considered a food or a part of a food that provides a health benefit. The overall goal of this work was to evaluate the efficacy of mannoheptulose (MH), a seven carbon sugar found in avocados, as a novel nutraceutical for canines. The metabolic effects of MH are ascribed to its ability to competitively inhibit hexokinases. When given at doses greater than 1 g/kg intravenously or intra-arterially, MH transiently elicits profound hyperglycaemia and hypoinsulinemia. These findings suggest that doses greater than 1 g/kg are supra-physiological. The ability of MH to transiently lower the insulin to glucagon ratio could be of benefit to overweight animals as it would promote lipid oxidation. However, few studies have examined the metabolic effects of low doses of MH on metabolism. Three experiments were undertaken to assess the effects of low oral doses of MH (2 mg/kg, Chapter 3; 4 mg/kg, Chapters 4 and 5; 8 mg/kg, Chapter 2) on fasting and post-prandial energy expenditure and macronutrient metabolism in healthy adult dogs. Overall, oral MH supplementation, at any dose, did not significantly affect macronutrient metabolism. A pilot study using a dietary dose of 2 mg/kg MH did not find any statistically significant effect of MH on plasma glucose kinetics or energy expenditure. At a dietary dose of 4 mg/kg, MH decreased voluntary physical activity as measured by an accelerometer, and transiently decreased dietary thermogenesis and respiratory quotient. In contrast, MH fed at a dose of 8 mg/kg in the presence of a high carbohydrate relative to fat diet (54% carbohydrate, 11% fat) transiently increased dietary thermogenesis. These findings suggest that oral MH has differential effects on energy expenditure depending on the administered dose and macronutrient composition of the diet. Irrespective of MH, these experiments are the first to assess post-prandial glucose and lipid kinetics in canines using stable isotope tracer and indirect calorimetry techniques. Such information is pertinent and provides a basis for quantitative measures of macronutrient metabolism in dogs.