Effects of dietary β-conglycinin on energy expenditure and lipid metabolism in Otsuka Long-Evans Tokushima Fatty (OLETF) rats

Background and objectives: Beta-conglycinin (β-CON), one of the major components of soy protein (SOY), has been shown to lower body fat mass and lipid levels. The effects could be partly associated with an increase of serum adiponectin concentration. Since adiponectin was demonstrated to control energy metabolism, the feeding of β-CON could also modulate energy consumption. In the present study, therefore, we examined how β-CON affected energy expenditure and lipid metabolism in obese Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Methods: The 14% high-fat diets were prepared according to the AIN-93G formula, containing either 20% casein (CAS), or the CAS replaced with SOY or β-CON at the proportion of 50%. The animals (5 week-old) were fed with the diets for 6 weeks. On day 35, the respiratory quotient was measured to calculate energy expenditure. After the feeding period, blood was collected from the abdominal vena cava and serum was prepared. The liver, white and brown adipose tissues and soleus muscle were excised. Results: Total energy consumption in the β-CON group was significantly higher than that in the CAS and SOY groups, concomitant with an increase of serum adiponectin level. Final body weight in the β-CON group was significantly lower than that in the CAS and SOY groups, while food consumption was comparable among the groups. The expression of genes related to energy metabolism (i.e. peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and carnitine palmitoyltransferase 1b (CPT1b) in the soleus muscle and uncoupling protein 1 (UCP1) in the brown adipose tissue) was higher in the β-CON group than in the CAS and SOY groups. The mesenteric adipose tissue weight was also significantly lower in the former than in the latter. Dietary β-CON compared with CAS decreased triglyceride concentration in the liver, being associated with a decrease of fatty acid synthesis and an increase of fatty acid β-oxidation in the liver. Conclusions: The results suggested that dietary β-CON was involved in energy expenditure to improve lipid metabolism through an increase of serum adiponectin concentration in OLETF rats.