Intermittent fasting and mental and physical fatigue in obese and non-obese rats

Intermittent fasting (IF) is an alternating pattern of restricting eating. This study evaluated mental and physical fatigue secondary to IF (daily 18-hour fast, 7-days-a-week) in the high-fat diet (HFD)-induced male obese Sprague Dawley rats. Fifty-four rats were randomly assigned to a HFD (n = 28) or a standard diet (SD; n = 26). After six weeks, the HFD rats were divided into one of four groups: obese HFD ad libitum (OB-HFD-AL), obese HFD-IF (OB-HFD-IF), obese SD-AL (OB-SD-AL), and obese SD-IF (OB-SD-IF). Similarly, non-obese controls were grouped into HFD-AL (C-HFD-AL), non-obese HFD-IF (C-HFD-IF), non-obese SD-AL (C-SD-AL), and non-obese SD-IF (C-SD-IF). After 2 weeks of IF, mental and physical fatigue were measured using open field (OF) and novel object recognition (NOR) tests. Rats on IF gained weight at a slower pace (p<0.05) and had lower glucose levels (p<0.01) compared to the AL group. In non-obese rats, ketone levels were higher in the IF-HFD group than IF-SD (p<0.05) and AL-SD (p<0.01) animals. Obese rats exhibited elevated blood ketone levels in IF-SD conditions versus AL-SD rats (p<0.01). AL-HFD rats had higher ketone levels than AL-SD animals in both obese and non-obese groups (p<0.05). In conclusion, rats with higher blood ketone levels, whether they were on IF or AL, traveled a greater distance during OF suggesting a lack of physical fatigue. There was no significant difference between IF and AL during NOR indicating a lack of mental fatigue. Thus, IF results in reduced body weight and blood glucose levels but does not induce physical or mental fatigue.