The Effects of Diet‐Induced Obesity in Male Sprague Dawley Rats on Blood Glucose, Ketones and Markers of Mental and Physical fatigue

Abstract

ObjectivePrevious studies on the pathology of obesity and obesity‐induced metabolic disorders utilized genetically modified obese rat models. To better mimic the onset and the physiology of obesity in humans, the use of diet‐induced obese rat models is lacking. Therefore, the purpose of this study is to induce obesity in Sprague Dawley rats by administering a high fat (HF) diet and to further investigate the effects of obesity on blood glucose and ketone concentrations as well as locomotor and mental activities as indicators of fatigue.MethodsFifty‐four 7‐week‐old male Sprague Dawley rats were randomized into either a high‐fat diet (HFD) group (n=28) or a standard diet (SD) group (n=26). All rats were housed in individual cages under controlled laboratory conditions and had access to food and water ad libitum. The HFD group received a HF diet (60% fat, 20% CHO, and 20% Pr) for six weeks, while the SD group received a standard diet (17% fat, 56% CHO, 27% Pr). Body weight (BW) was measured weekly and blood glucose and ketones were measured twice a week for 6 weeks. The open field test (OF) was conducted daily for 8 days in week 5, followed by Novel object recognition (NOR) testing at 4 separate days during week 6.ResultsBoth groups gained weight from week 1 to week 6 (HFD: 223.0±16.2g vs. 387.7±23.6g, p<0.001; at week 1 vs. week 6, respectively, SD: 215.0±15.9g vs. 361.5±23.6g, p<0.001; at week 1 vs. week 6, respectively). However, the average within‐subject BW gain was greater in the HFD compared to the SD (168.1±21.6g vs 130.1±16.9g, p<0.001; HFD vs. SD, respectively). Although the average glucose levels were not different between the two groups throughout the study, the HFD showed higher fluctuations of blood glucose levels and at week 4 they had higher glucose levels than the SD (104.1±11.2mg/dL vs. 96.6±6.9mg/dL, p=0.005; for HFD vs. SD, respectively). Ketone levels were not different between the two groups. Although there were no overall differences in OF and NOR test results in HFD vs. SD, the difference between the recognition time of the familiar vs. the novel object in the HFD tended to be smaller than that of the SD at all 4 days of NOR testing (p=ns).ConclusionsThe HF diet results in significant weight gain consistent with obesity in the majority of rats within a 6‐week period of receiving the diet. Overall, diet‐induced obesity was not found to have adverse effects on glucose and ketone levels. However, it might negatively affect memory and lead to mental fatigue in rats.