SummaryObesity is the presence of excess body fat and is associated with a variety of medical conditions which increase morbidity and mortality. Millions of individuals participate in weight-reduction programmes which include reduced calorie diets and may also include exercise. Very low calorie diets (VLCD) of 400 to 800 kcal/day appear attractive as they generally show an increase in weight loss from 0.2 to 0.5 kg/week found with the traditional diet to 1.5 to 2.0 kg/week. Early use of very low calorie diets with poor quality protein and loose medical supervision resulted in about 60 deaths, many of which were attributed to loss of lean body mass and in particular, cardiac muscle atrophy. Although current very low calorie diets are presumed safe, concern regarding preservation of lean body mass (LBM) remains. Investigators have used exercise to slow the depletion of lean body mass during very low calorie diets; however, the results are not conclusive. A host of different methodologies and questionable documentation and design of exercise protocols precludes a definitive statement for the benefits of exercise during very low calorie diets for the purpose of LBM retention.