| Objectives:Rudermat introduced a new term'metabolically obese, normal-weight' (MONW) in 1981. He suggested that individuals exist who are not obese on the basis of height and weight, but metabolically abnormal similar to obese subjects. Recently, it was reported that the degree of obesity was not correlated with the caloric diet as the greatest body weight was found in rats fed with the lower energy content, conversely, the highest caloric diet did not lead to a significant increase in body weight compared with control animals. It was concerned with fat-to-carbohydrate ratio. The aim is to make up MONW rat model with high temperature baked high-fat high-sucrose diet to be used in further study for the pathogenesis and management of MONW.Methods:1. The make up of the high-fat high-sucrose diet. The high-fat high-sucrose diet was composed with 0.83% calcium,0.65% phosphonium, 3% egg yellow flour,18% pork fat,25% sucrose and 59% SPF animal feeds. After agitated with water sufficiently, they were baked at 160℃for an hour, then turned off the fire and kept them in the baker all the night. The total calorie of the high-fat high-sucrose diet was 21.37 kJ/g, protein account for 15%, carbohydrate account for 51%, fat account for 25%.2. For the experiment, a total of 60 male Sprague-Dawley (SD) rats,4 weeks old, weighing 60g-70g upon their arrival, were kept at appropriate temperature and humidity under a 12h light/dark cycle and had ad libitum access to standard food and tap water for 4 weeks. Then they were randomly divided into two groups:①The high-fat h gh-sucrose group was fed with high-fat high-sucrose diet (40 rats);②The control group was fed with normal diet (20 rats).Every week measured body weight of each rat. After 8 weeks with the high-fat high-sucrose diet, the animals were orally gavaged with 2 g/kg body weight of glucose dissolved in water (40%, wt/vol). In this experiment, there were 6 rats dead. So there were 36 rats in the high-fat high-sucrose group, and 18 rats in the control group in the end.3. Blood glucose levels were measured at 0,2h with the glucose meter. (glucose dehydrogenase method, tip strip Optium Xceed, Roche Co Ltd, Germany). After 21 weeks with the high-fat high-sucrose diet, the animals were gavaged with 2 g/kg body weight of glucose dissolved in water (40%, wt/vol) again. Blood glucose levels were measured at 0,0.5,1,1.5, and 2 h with the glucose meter.4. For the study of the effect of a high-fat high-sucrose diet on fasting serum insulin, overnight fasting and blood samples were collected from angular veins and centrifuged, and serum was kept at-80℃until use for insulin determination (ELISA kit for rats from Mercodia Diagnostics, Sweden).5. For the study of the effect of the high-fat high-sucrose on the diabetes mellitus type 2 induction rate with streptozotocin (STZ). STZ was dissolved in citrate buffer (pH 4.1) with a conceatration of 1%. Rats (29 weeks old) that fed with high-fat high-sucrose diet were divided into two groups:Group 1 (n=15) was injected with STZ (30mg/kg), Group 2 (n=11) was injected normal saline intraperitoneally. Rats (29 weeks old) that fed with regular forage were divided into two groups:Group 3 (n=9) was given the same dosage of STZ as in the high fat high-sucrose group, Group 4 (n=9) was injected normal saline. One week after injection, rats were fasted overnight. In the next morning fasting blood glucose level and OGTT 30, 60,90,120 min was measured. Diabetes mellitus type 2 was made when plasma fasting tail blood glucose (FPG)≥7.0mmol/L or OGTT 120min blood glucose (OGTT 2h)≥11.0mmol/L. Results:1. There were no differences in the body weight between the high-fat high-sucrose diet group and the control group when they were 8 weeks old (P>0.05).2. From the 1st week to the 21st week after high-fat high-sucrose diet, there were no differences in the body weight between the high-fat high-sucrose diet group and the control group (P>0.05). There were no differences in the increasing of every weekly body weight between the two groups (P>0.05). In the 21st week, the level of body weight of the high-fat high-sucrose+STZ group, the high-fat high-sucrose+NS group, the control +STZ group and the differences were significant compared with the control group+NS group.3. In the 16 weeks old, rats in the high-fat high-sucrose diet group had higher (P<0.05) blood glucose level at time points 2 hours, the fasting blood glucose was not significant(P>0.05).4. In the 29 weeks old, rats in the high-fat high-sucrose diet group had higher blood glucose level at time points 0,0.5,1 and 1.5 h and it was significant (P<0.05). The glucose tolerance of the high-fat high-sucrose diet group was impaired.5. There was significant in the differences of the blood glucose when the high-fat high-sucrose diet rats were 16 weeks old compared with 29 weeks old (P<0.05). But the differences of the control group were not significant (P>0.05).6. The level of fasting serum insulin of the high-fat high-sucrose diet group higher than the control group and it was significant (P<0.05). There was insulin resistant in the high-fat high-sucrose diet group.7. In the control group with STZ there was one rat with FPG≥7.0mmol/L, and two rats with OGTT 2 h≥11.0mmol/L. While in the high-fat high-sucrose diet group there were eleven rats with FPG≥7.0mmol/L, and all the rats with OGTT 2 h≥11.0 mmol/L. There was significant at fasting blood glucose and OGTT 2 h between the high-fat high-sucrose group and the control group (P<0.05), and the high-fat high-sucrose group was higher than the control group. The high-fat high-sucrose group was higher than the control group in the incidence of STZ-induced diabetes mellitus type 2.ConclusionsHigh temperature baked diet containing high-fat high-sucrose does not increase body weight, but led to a metabolically abnormal state of insulin resistant and increased incidence of STZ-induced diabetes. Thus, a MONW rat model could be achieved with high temperature baked high-fat high-sucrose diet that can be used in further study for the pathogenesis and management of MONW.
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