Obesity is a leading health problem in the United States, despite the abundance of weight-loss programs available. There is an increasing interest in weight-loss methods that use time-restricted feeding, including intermittent fasting, where days of limited food access are alternated with days of normal food intake. To determine the benefits of intermittent fasting to obesity, we employed a rat model of inherent leanness and obesity, with the lean rats being more physically active (high-capacity runners) than the obesity-prone (low-capacity runners). Our hypothesis stated that intermittent fasting would induce loss of fat and lean mass in both rat types with the obesity-prone rats losing more body weight. Body weight and composition were measured before intermittent fasting in lean and obesity-prone male rats (n=8/group). Rats were allowed free access to food on fed days, alternating with fasting days (no calories consumed). Rats were weighed daily and the body composition was analyzed weekly using magnetic resonance spectroscopy (EchoMRI). All rats lost weight over eight weeks of intermittent fasting. Obesity-prone rats lost significantly more fat mass and body weight compared to the lean rats, whereas loss of lean mass differed by only a few grams. Results were similar in female rats but contrasted with previous findings when weight loss was induced using 50% calorie restriction. Compared to standard calorie restriction, intermittent fasting decreased the loss of lean mass while enhancing the loss of fat mass. Intermittent fasting was thus found to be successful in inducing weight loss in obese rats.