Calories are units of energy that drive body processes and make it possible for you to live. With the exception of water or diet soda, virtually all other foods contain at least a few. As Kids Health notes, to maintain a healthy weight you need to strike a balance between the calories you consume and the calories you burn. If you consume more than you burn, weight gain and the health problems that come with it, are natural results. Conversely, if you consume too little, weight loss and its associated health problems can also occur.
You can divide the calories you consume each day into two groups; those you need to stay alive and those you need for physical activity. The number of calories in the first group, called your resting or basal metabolic rate, depends on factors such as your gender, age, height and weight. According to Flavia Herzog, a registered dietitian specializing in pediatric nutrition, the average RMR is 1,000 to 1,400 calories each day. Falling below this number has an effect on your body and your overall health.
If you are trying to lose weight, consuming too few calories in a day can significantly alter weight loss goals. According to the consumer health information site Net Wellness, if your calorie intake falls below 50 percent of your RMR, your body goes into starvation mode. As this occurs, fat metabolism stops and lean tissue and muscle mass metabolism begins. According to registered dietitian and writer Juliette Kellow, as you begin losing muscle mass, metabolism slows ever further as decreasing muscle and tissue mass requires less energy to function, and weight loss slows or stops.
Too few calories have an effect on blood sugar levels. Normally, metabolism causes blood sugar levels to increase as food energy in the form of glucose enters your bloodstream. Insulin, produced and secreted by your pancreas, helps glucose get into body cells and tissues, bringing blood sugar back down to normal levels. According to the University of Maryland Medical Center, too few calories cause a reduction in blood sugar levels that can lead to a condition called hypoglycemia. Symptoms of hypoglycemia include depression, anxiety, irritability, trembling and heart palpitations.
Continually consuming too few calories in a day can lead to the development of an eating disorder called anorexia nervosa. According to Help Guide, a nonprofit health information site, anorexia nervosa has the potential to affect hormone production, fluid balance and every organ in your body. Early symptoms of anorexia nervosa can include fatigue, constipation, body chills, headaches and dizziness. Later symptoms can include disruption of menstrual periods in women, jaundice, changes in brain chemistry, kidney or heart failure.
An eventual return to your pre-diet weight is a typical consequence of consuming too few calories in an attempt to lose weight. According to Net Wellness, this can make further attempts to lose weight more difficult for two reasons. First, your metabolism is slower due to decreased muscle mass and second, the weight you gain back is fat that requires a high metabolic rate to burn.