Normocaloric Diet Restores Weight Gain and Insulin Sensitivity in Obese Mice

Abstract

An increased incidence of obesity is registered worldwide, and its association with insulin resistance and type 2 diabetes is closely related with increased morbidity and mortality for cardiovascular diseases. A major clinical problem in the management of obesity is the non-adherence or low adherence of patients to a hypocaloric dietetic restriction. In this study, we evaluated in obese mice the effects of shifting from high-calorie foods to normal diet on insulin sensitivity. Male C57BL/6JOlaHsd mice (n = 20) were fed with high fat diet (HFD) for a 24-week period. Afterward, body weight, energy, and food intake were measured in all animals, together with parameters of insulin sensitivity by homeostatic model assessment of insulin resistance and plasma glucose levels in response to insulin administration. Moreover, in half of these mice, Glut4 mRNA levels were measured in muscle at the end of the high fat treatment, whereas the rest of the animals (n = 10) were shifted to normocaloric diet (NCD) for 10 weeks, after which the same analyses were carried out. A significant reduction of body weight was found after the transition from high to normal fat diet, and this decrease correlated well with an improvement in insulin sensitivity. In fact, we found a reduction in serum insulin levels and the recovery of insulin responsiveness in terms of glucose disposal measured by insulin tolerance test and Glut4 mRNA and protein expression. These results indicate that obesity-related insulin resistance may be rescued by shifting from HFD to NCD.

Keywords: Glut4; diet; glucose; insulin resistance; obesity.

Figure 1

Study design. A schematic representation of the study protocol and experimental plan is shown.

Figure 2

Effects on body weight, food, and energy intake in mice fed with high fat diet (HFD) for 24 weeks and with normocaloric diet (NCD) for other 10 weeks. A significant reduction of body weight and energy intake was observed in NCD mice (A,B), whereas no significant difference was detected in food intake (C). Body weight over the time is shown in the inset. Values are expressed as mean ± SD. *p < 0.001.

Figure 3

Biochemical parameters. Blood samples were collected as indicated in Section “Materials and Methods.” After 10 weeks of feeding with a normocaloric diet (NCD), mice showed a significant reduction of plasma glucose levels and serum insulin levels, as well as a reduction in both triglycerides and total cholesterol when compared to the HFD. Values are expressed as mean ± SD. *p < 0.05.

Figure 4

Insulin sensitivity. HFD and NCD mice fasted for 12 h were injected intraperitoneally with insulin (1 U/kg). Blood glucose levels were measured with a glucometer, as reported in Section “Materials and Methods.” Values are expressed as mean ± SD. *p < 0.05.

Figure 5

Expression of Glut4. Glut4 mRNA levels were measured by qRT-PCR in skeletal muscle from HFD and NCD mice, after insulin stimulation. Results are the mean ± SD for six animals per group. *p < 0.05 versus HFD mice. A representative Western blot (WB) of Glut4 in quadriceps muscle from six to eight mice of each group is shown in duplicate in the autoradiogram. Gapdh, control of protein loading.