Dietary Mannoheptulose Does Not Significantly Alter Daily Energy Expenditure in Adult Labrador Retrievers

Abstract

Mannoheptulose (MH), a sugar found in avocados that inhibits glycolysis in vitro, has been preliminarily investigated as a novel food ingredient for dogs. This study aimed to determine the effects of dietary MH, delivered as an extract of un-ripened avocado, on energy expenditure (EE) in healthy adult Labrador Retriever dogs (total of 12 dogs, 26.99 ± 0.634 kg, 4.9 ± 0.2 y). The study was a double-blind, cross-over with each dog receiving both dietary treatments, control (CON) and MH (400 mg/kg of diet; 6 mg/kg BW), in random order. Resting and post-prandial (10 h) EE and respiratory quotient (RQ) were determined by indirect calorimetry (d 42). The following day, body composition was assessed using dual X-ray absorptiometry. Continuous activity monitoring was conducted using an Atical® accelerometer (d 43–47). A vastus lateralis muscle biopsy was obtained prior to the morning meal (d 49) and 4 h after consumption of their meal (d 56) to determine the protein content and phosphorylation of 5' adenosine monophosphate-activated protein kinase (AMPK). Diet did not affect body weight, resting EE or skeletal muscle AMPK phosphorylation. Dogs fed MH had significantly lower post-prandial RQ (p = 0.02) and ratio of fat to lean body mass (p = 0.02). Physical activity during light time periods (but not dark) was lower in dogs fed MH (p < 0.05) during weekends, but not on weekdays. These results suggest that MH affects energy balance of adult dogs, but that these effects are not dose dependent and not due to physical activity.

Characterization and Mechanisms of Action of Avocado Extract Enriched in Mannoheptulose as a Candidate Calorie Restriction Mimetic

“…McKnight et al 32 also found no significant effects of an AvX diet delivering 6 mg/kg for 9 weeks on plasma glucose kinetics in Labrador Retrievers but did observe significantly reduced postprandial RQ. It is unclear why the differences between these past reports and the findings reported herein occurred regarding the effects of AvX on glucose and insulin levels.…”

An Avocado Extract Enriched in Mannoheptulose Prevents the Negative Effects of a High-Fat Diet in Mice

“…In Labrador Retrievers fed an AvX diet delivering 2 mg/kg of MH for 22 days, McKnight et al [ 46 ] observed significantly increased fasting RQ and glucose oxidation measured by calorimetry. In another study of Labrador Retrievers eating an AvX diet delivering 6 mg/kg of MH for 9 weeks, McKnight et al [ 47 ] also observed significantly reduced post-prandial RQ. It is uncertain why differences between these past studies in dogs and cats and the current findings in mice occurred regarding the effects of AvX on glucose and insulin levels.…”

“…Some previous studies applying a similar formulation of MH-enriched AvX in studies of dogs and cats have produced results that are incongruent with those of our mouse study. Ranging from 14 to 42 days of treatment delivering MH doses from 2 to 8 mg/kg, investigations of Labrador Retrievers, Beagles, and domestic cats found no significant effects on circulating levels of glucose or insulin nor on body weight [ 43 , 44 , 45 , 46 , 47 ]. Several significant physiological effects of feeding AvX were observed, however.…”

Caloric Restriction Mimetics in Nutrition and Clinical Trials

“…Resveratrol , which is discussed later in the review in more detail, also shows anti-glycolytic activities, as it shows inhibitory effects on hexokinase in cell lines ( 97 ). Apart from these phenolic, plant-based compounds, mannoheptulose , a rare sugar, also inhibits hexokinases and was suggested as a CRM which is prominently present in unripe avocados ( 98 ), but has produced mixed results in preclinical work ( 17 ).…”