Low-fat diet results in lower respiratory quotient during caloric restriction and refeeding than other diets but it is not a predictor of greater body fat burning in mice

Abstract

Background. Weight regain following weight loss is a frequent problem that people with obesity or athletes of weight-making sports face (Fothergill et al., 2016). It is suggested that diets high in carbohydrate or protein decrease or increase energy expenditure, respectively, and thus affect energy balance and success of weight maintenance (Ebbeling et al., 2018; Oliveira et al., 2021). Our goal is to examine the role of diet composition on weight maintenance and energy metabolism in aged mice during caloric restriction (CR) and post-dieting period (P-CR). Research methods. Males of C57BL/6J mouse strain were grown until 18-month-old and then mice with overweight were selected and divided into 4 groups matched by body mass: low-fat (20, 20, 60% of kcal from fat, protein, carbohydrate), low-carbohydrate (60, 20, 20%, respectively), high-protein (30, 35, 35%, respectively) and control (regular chow diet) (n = 9–11 each). Mice were subjected to 30% CR for 4 weeks followed by ad libitum P-CR feeding for 4 weeks using the same diets. Controls were fed ad libitum all the time. Body mass and 23-h indirect calorimetry in metabolic cage (energy expenditure, respiratory quotient, physical activity levels) were assessed during CR and P-CR. Results and discussion. Weight loss was similar between the diet groups during CR (p > 0.05) but only low-carb group regained more weight in P-CR than had initially prior CR. Energy expenditure did not differ between diet groups neither during CR nor P-CR (p > 0.05) but was lower in CR and higher in P-CR compared to controls. Energy expenditure normalized to body mass was similar between diet groups during CR but lower in low-carb group during P-CR compared to high-pro and especially low-fat group (p < 0.001). Physical activity did not differ between diet groups neither during CR nor P-CR (p > 0.05). Respiratory quotient was significantly lower in low-carb group compared to all groups during both CR and P-CR (p < 0.01–0.001). Conclusions. Low-carb diet is associated with greater weight regain and lower relative energy expenditure after previous weight loss compared to other type of diets in aged mice. Low respiratory quotient in low-carb diet indicates overall fat metabolism and oxidation (from diet + body storage) and is not a good predictor of burned body fat.