Effects of Under Eating Not eating enough is equally as bad as not eating a healthy diet. Poor eating habits will affect your body developing with lack of nutrients. Not eating enough may result in loss of muscle mass, lack of energy and poor recover from exercise. Loss of Muscle Mass During a workout your muscles will get tears and get strained. This will release stress hormones in your body. If you are not eating enough your body will get under constant (chronic) stress which will result in muscle catabolism even on not working. To recover your muscles need carbohydrates, protein and fats. Not eating enough nutrients will mean your body will get them from somewhere .Fat and muscle loss is a clear sign on under-eating. Take notice and start to eat right kinds of food. No Lose in Fat It would sound like the opposite effect but under-eating will gain you weight. Few things are happening in this case such as stress hormones will increase and they promote fat storage. Starvation is the reaction will cause on under-eating. Your body will burns muscle instead of fat to store more energy. The lesser you will eat and the worser you will become. Losing muscle mass for energy will slower the metabolism.