Or you can do a combination of both. Eliminate 250 calories and perform about half hour of cardio, which will burn through about 250 calories. Most experts recommend only shedding two pounds -- any more than that can either be water weight or muscle.{relatedarticles}Losing muscle is detrimental - the more muscle you have, the harder your metabolism works when your body is at rest. To prevent muscle loss, it's important to consume at least 1,200 calories a day. The other dangers of rapid weight loss include dehydration, malnutrition, diarrhea and fatigue.