The ¹³C-bicarbonate technique as a tool for measurement of energy expenditure in overweight dogs undergoing body weight reduction and the effect of different dietary composition

Changes in body size and composition, i.e., body weight (BW) gain or loss, affect the daily energy expenditure (EE). To ensure an appropriate BW reduction and to find an efficient strategy to reduce and maintain a target BW, regular evaluations and adjustments of energy allowance are important. This study aimed to provide a detailed knowledge about the possible changes in resting EE using the oral C-13-bicarbonate technique (o(13)CBT) as a research tool in 16 overweight pet dogs undergoing BW reduction. Dietary composition (i.e., in % of dry matter [DM] being a high protein [33.3], low fat [9.6], and high crude fiber [18.0] diet [LFHFibre], and a high protein [37.9], high fat [52.0], carbohydrate-free diet [H-Fat]) during 16 wk of energy restriction were evaluated regarding effects on resting EE, rate of BW reduction, body composition, and plasma concentrations of metabolic hormones involved in energy metabolism and appetite regulation. The mean BW loss was higher (P<0.05) for the dogs fed the LFHFibre diet (1.1%/wk) than that for dogs fed the H-Fat diet (0.8%/wk), but the total BW reduction of 14.6% and 12.0% of initial BW did not differ significantly (P>0.05). Resting EE was lower (P<0.02) after the BW reduction; 414 kJ (99 kcal)/kg BW0.75/d at the start (week 0) and 326 kJ (78 kcal)/kg BW0.75/d at the end (week 16) of the study. The BW reduction in both groups (P>0.05) consisted of both fat mass (FM) and fat-free mass (FFM). Energy expenditure, calculated in relation to amount of FFM, was not significantly (P>0.05) affected by BW reduction. Dietary composition did not significantly affect (P>0.05) plasma concentrations of insulin, leptin, and ghrelin, and no effect (P>0.05) of BW reduction was observed on hormone concentrations. In conclusion, the o(13)CBT proved to be a useful research method for studying short-term EE in overweight dogs. Even though all dogs lost BW, most dogs were still overweight at the end of the study. Due to a high individual variation among dogs, a longer experimental period with a larger sample size would be desirable. Changes in body size and composition, such as body weight (BW) loss, affect daily energy expenditure. The minimally invasive C-13-bicarbonate technique can be an efficient research tool for measuring energy expenditure in overweight dogs undergoing weight loss (WL) programs, thus allowing for adjustment of energy supply so that WL and achieved target BW can be maintained. Lay Summary The most common nutritional disorder in dogs is overweight, and knowledge about dogs' energy requirement is therefore important to adjust daily feed allowance. Changes in body weight may affect energy expenditure (EE) and, thereby, energy requirement. This study aimed to measure such potential changes under resting conditions in overweight dogs. It was found that the minimally invasive C-13-bicarbonate technique was a useful research method for studies regarding EE during weight loss (WL) in dogs. EE decreased when the dogs lost weight, and energy allowance needed to be reduced to maintain WL. The second objective of this study was to evaluate the effects of feeding diets with different macronutrient compositions on EE, rate of WL, body composition, and plasma concentrations of hormones involved in energy metabolism and appetite regulation. The mean WL rate was slightly higher for dogs fed a diet with high protein, low fat, and high crude fiber contents than those fed a carbohydrate-free diet with a high protein and fat contents. However, diet did not affect the resting EE, measured plasma hormone concentrations, or the total WL at the end of the study.