Combined Effects of Dietary Protein Type and Fat Level on the Body Fat-Reducing Activity of Conjugated Linoleic Acid (CLA) in Rats

Asuka AKAHOSHI, Kazunori KOBA, Rie ENMOTO, Kazuko NISHIMURA, Yukiko HONDA, Miyuki MINAMI, Keiko YAMAMOTO, Toshio IWATA, Yoshie YAMAUCHI, Kentaro TSUTSUMI, Michihiro SUGANO
2005 Bioscience, biotechnology and biochemistry  
The interaction of dietary protein type and fat level on the body fat-reducing activity of conjugated linoleic acid (CLA) was studied in male rats fed diets containing casein (CAS) or soy protein (SOY) as a protein source with low fat (LF, 6.0% soybean oil) or high fat (HF, 13.0% soybean oil) combinations for 4 weeks. CLA was added at the 1.0% level to all diets. The weight of perirenal adipose tissue tended to be lower in the SOY groups than in the corresponding CAS groups, and the difference
more » ... and the difference between the LF diets was significant. The weight of epididymal adipose tissue showed a similar but insignificant trend. The weight of brown adipose tissue was heaviest on the SOY-HF diet and lowest on two CAS diets, the SOY-LF diet being intermediate. The concentration of serum leptin was lowest on the SOY-LF diet and was significantly lower than that of the corresponding CAS group, but this difference disappeared when the dietary fat level increased. The serum cholesterol-lowering activity of SOY in relation to CAS was reproduced even when CLA was given. Thus the body fat-reducing activity of CLA was most marked when rats were fed the SOY-LF diet. Although the CAS-HF diet increased body fat deposition, the magnitude of the reduction by lowering dietary fat level was more marked than in the case of SOY. These results indicate a complicated interaction of dietary manipulations with the body fat-reducing effect of CLA, but the combination of CLA with the SOY-LF diet appears to be an appropriate approach. Conjugated linoleic acid (CLA) has many known beneficial health effects such as anti-carcinogenic, anti-obesity, and anti-atherogenic activities, 1-6) but the magnitude of response to CLA differs from animal species to species, and humans appear to be the least responsive animal. 7,8) A line of human studies on the body fat-reducing activity of CLA showed equivocal results under a wide range of dose level, [9] [10] [11] [12] although one recent study showed staple body fat-reducing potential of CLA in the long term human trials. 13) It is, therefore, reasonable to examine the effect of dietary components that enhance the activities of CLA. This approach might additionally help to lower possible unfavorable side effects of CLA 14-16) by reducing dietary intake of it. If the reinforcing effects of various food ingredients on the physiological functions of CLA are defined, CLA will be more beneficial for humans. In a preceding study on rats, we showed that the body fat-reducing activity of dietary CLA can be enhanced by combination with sesamin, a lignan occurring abundantly in sesame seeds. 17) Although it is well-known that soybean protein in relation to casein reduces body fats, the beneficial interaction of this protein with CLA has not been well clarified in this animal model. 18) Thus insight into the interaction of dietary protein sources opens a new approach to dietary reinforcement of the physiological functions of CLA. It is also interesting to define the effect of dietary fat level on CLA effects, because dietary fat level appears to influence the effect that CLA exerts on the diabetic state. 19) In this context, we studied in more detail the modifying effects of dietary protein type and fat level on the body fat-reducing activity of CLA in rats. Thus in the present study growth parameters, weights of adipose tissues, concentrations of serum components related to lipid metabolism, and hepatic fatty acid -oxidation activity were measured in rats fed 1% CLA diets containing either SOY or CAS with low (6%) or high (13%) levels of dietary fat (soybean oil).
doi:10.1271/bbb.69.2409 pmid:16377901 fatcat:6mn6mrb4x5anrmb6wkcpwx3n5i