Low-carb diet (low carb diet): an eating plan that reduces or limits carbohydrates, instead emphasizing foods that are high in protein or fat. Carbohydrates are found in grains, starchy vegetables, pasta, sugary foods, and fruits. There are many different types of low-carb diets. The theory behind the popularity of low-carb diets for weight loss is that lowering one's consumption of carbohydrates lowers insulin levels, which results in burning stored body fat for energy. Examples of popular low-carb diets include the Atkins and South Beach diets.