Postprandial Responses of Energy Substrates in Dogs Fed High Fat‐ vs High Protein‐Low Carbohydrate Ketogenic Foods Relative to a High Carbohydrate Food

Abstract

ObjectiveReduction of dietary carbohydrate (CHO) can increase circulating ketone availability and may aid disease management including inflammatory bowel disease, cancer, diabetes and cognitive decline. Companion animal dogs are prone to all of these maladies. Postprandial to a mixed macronutrient meal, non‐esterified fatty acids (NEFA) and beta‐hydroxybutyrate (BHB) decrease. In contrast, both glucose and blood urea nitrogen (BUN) increase. Triglycerides (TG) comprise circulating fat energy after a fat‐containing meal although medium chain TG (MCT) are preferentially catabolized to ketones. The postprandial responses of dogs to habitual feeding of high fat versus high protein low CHO foods, relative to high CHO foods, is not known. Therefore, we compared fasting (0 hr) and 2‐0 hr delta values for BHB, NEFA, TG, glucose, BUN as markers of available energy for these foods in dogs.MethodsDogs housed in pairs, with daily group exercise in outdoor grassy runs. Dogs returned to the colony healthy after the study; no invasive procedures. Blood collections under approved protocols at 0 hours (immediately before a meal) and at 2 hours postprandial. Macronutrients (P/F/C; % energy) for the 3 foods: HiCHO (25/37/38); LoCHOprot (50/44/6); LoCHOfat (28/68/4). The LoCHOfat food further contained 22% of dietary fat energy as MCT. Prospective randomized crossover trial (2 groups, n = 18). HiCHO was the wash‐in food followed by LoCHOprot or LoCHOfat in randomized order (5 wk feeding each food). Foods analyzed according to AOAC methods. Energy substrates BHB, NEFA, TG, glucose and BUN measured by Cobas or enzymatic reaction. Individual diet differences by dependent samples t‐test, linear mixed modeling for overall diet effect. Significance at α = 0.05.ResultsAnalyzed ketogenic ratios of the foods: HiCHO (0.46), LoCHOprot (1.1), and LoCHOfat (1.7). At fasting, LoCHOprot and LoCHOfat elevated circulating BHB above HiCHO food with LoCHOfat BHB higher than LoCHOprot. Between 0‐2 hours postprandial, BHB decreased for HiCHO (‐23%) and increased more for LoCHOfat (+100%) than LoCHOprot (+33%). Fasting NEFA were higher in LoCHOprot than LoCHOfat, and not different otherwise. From 0‐2 hours postprandial all foods showed decreased NEFA: HiCHO (‐43%), LoCHOprot (‐57%), LoCHOfat (‐12%). Fasting glucose was not different between groups. From 0‐2 hours postprandial LoCHOprot (‐4%) and LoCHOfat (‐8%) showed decreased glucose while HiCHO was unchanged. Fasting TG levels were different between all foods with the LoCHOprot (‐45%) and LoCHOfat (‐37%) lower than HiCHO. From 0‐2 hours postprandial all dogs showed increased TG with all values different between groups: HiCHO (+135%), LoCHOprot (+356%), LoCHOfat (+591%). Fasting BUN was higher with LoCHOprot than either HiCHO (‐27%) or LoCHOfat (‐26%). From 0‐2 hours postprandial all dogs showed increased BUN with all changes different: HiCHO (+17%), LoCHOprot (+42%), LoCHOfat (+23%).ConclusionsThe LoCHOfat food increased postprandial availability of BHB, NEFA and TG energy while decreasing glucose energy. LoCHOprot primarily enhanced available energy from protein as shown by increased amino acid catabolism to BUN, with additional contributions from BHB, NEFA and TG. The HiCHO food presented only glucose and TG as energy postprandial. Together these data show that a moderate protein, high fat, low CHO food with added MCT can selectively apportion postprandial energy toward ketone and fats while decreasing availability of glucose.