Effect of feeding a high‐carbohydrate or a high‐fat diet on subsequent food intake and blood concentration of satiety‐related hormones in dogs
The effect of the main macronutrients on food intake and on satiety‐related gut hormones has been widely studied in humans and rats as the incidence of obesity and metabolic‐related diseases gradually increases in Western countries. However, there have been comparatively few studies carried out in dogs and these have mainly focused on the effect of protein and fibre (Bosch et al., 2009; Weber et al., 2007). According to studies in humans, consumption of fat is closely related to body fat mass beyond any other individual factor (Tucker & Kano, 1992), and an increase in the fat to carbohydrate content of diets has been related to an increased energy intake in humans (Blundell, Burley, Cotton, & Lawton, 1993) and rats (Warwick, 2003) during ad libitum feeding tests. Over‐consumption of fat‐rich diets in these species may be associated with their high palatability, which can reinforce feeding behaviour even when energy needs have been satisfied (Erlanson‐Albertsson, 2005), but also to a weaker satiating capacity of fat. In this respect, a series of studies in humans (Blundell et al., 1993) and rats (Gaysinskaya, Karatayev, Chang, & Leibowitz, 2007) have evidenced a higher capacity of carbohydrates vs. fat to suppress food intake in the first two hours post‐prandial. It is uncertain whether feeding high‐fat diets to dogs may also result in energy over‐consumption, thus contributing to the high prevalence of obesity (McGreevy et al., 2005). Hitherto, the effect of fat and carbohydrates on food intake control remains understudied in dogs. Moreover, in a study conducted by Geoghegan, Cheng, Lawson, and Pappas (1997) in which the satiating capacity of isocaloric infusions of oleate and dextrose was determined in dogs by sham‐feeding at the end of small bowel infusion, the workers in this paper found a greater suppression of food intake with fat in comparison to dextrose. Although this finding suggests a greater satiating action of fat, it is debatable whether or not the satiety response observed in this study fully reflects the effect of orally administered nutrients that also elicit physicochemical signalling from the stomach.
Hormones released from the gastrointestinal tract or the pancreas exert either an orexigenic (i.e. ghrelin) or an anorexigenic [i.e. peptide YY (PYY), glucagon‐like peptide (GLP‐1) and insulin] action, their secretion being differentially evoked by fat and carbohydrates. Carbohydrates are regarded to be more efficient than fat in increasing blood levels of insulin (Gibbons et al., 2013; Monteleone, Bencivenga, Longobardi, Serritella, & Maj, 2003). Greater post‐prandial suppression of ghrelin induced by carbohydrates rather than fat has also been shown in rats (Overduin, Frayo, Grill, Kaplan, & Cummings, 2005) and humans (Monteleone et al., 2003; Yang et al., 2009), although these findings were not corroborated by two recent studies in humans (Gibbons et al., 2013; van der Klaauw et al., 2013) in which a similar ghrelin suppression was found after consumption of two isocaloric meals rich in either fat or carbohydrates. On the other hand, fat intake has been shown to increase blood levels of PYY at a similar (van der Klaauw et al., 2013) or greater extent than carbohydrates (Essah, Levy, Sistrun, Kelly, & Nestler, 2007; Gibbons et al., 2013; Yang et al., 2009), and to cause a higher rise of GLP‐1 (Gibbons et al., 2013; Paniagua et al., 2007) in humans.
We are aware of only a few studies that have evaluated the effect of fat and carbohydrates on satiety‐related hormones in dogs. In an early study conducted by Greeley et al. (1989), intraduodenal infusion of oleic acid resulted in a greater release of PYY in relation to intraduodenal infusion of glucose. More recently, Lubbs et al.