Undereating is defined as eating less food than the body demands to maintain its weight. Prolonged or severe undereating results not only in weight loss but also potentially dangerous muscle wasting. It may also lead to metabolic and psychological disturbances. Mild undereating is a necessary part of a planned weight-loss regime, but it should not be severe. It is important that the undereating results in a lower calorie intake but not a reduction in essential nutrients – especially vitamins and minerals. This usually means reducing the fat content of meals. Once the target weight is achieved, the dieter should revert to a well-balanced maintenance diet.
Undereating problems can also be due to psychological or physical reasons. If you are significantly underweight, this may indicate serious disease so please consider seeing a doctor as soon as possible.
As a result of fasting, skipping meals or eating too little, the body will try to conserve energy by producing less body heat, thus reducing your body temperature.