The human body requires a certain amount of calories to function, even for those who are sedentary. Not eating enough calories to meet those basic needs can cause a variety of physical and mental ailments, ranging from mild to severe. Knowing how many calories your body needs can help you avoid any issues that might arise from not eating enough.
The amount of calories the human body needs to function at a basic level is known as the basal metabolic rate, or BMR. The BMR is the amount of calories your body needs, while at rest, to perform basic functions such as blood circulation, organ function, breathing and temperature regulation. Your body also needs additional calories to provide energy for other activities, including digestion, exercising and the basic activities of daily life.
In medical terms, a sign is considered an objective phenomenon, such as an observable physical problem like a rash, while symptoms are subjective, meaning what the patient feels. Not eating enough calories can lead to a variety of signs and symptoms. Mild symptoms can include dizziness, feeling hungry, feeling irritable, shakiness and tiredness. This is the result of low blood sugar, which means your body doesn't have enough sugar -- called glucose, the body's basic fuel -- to perform its necessary functions. This is a condition known as hypoglycemia. According to the National Diabetes Information Clearinghouse, mild signs and symptoms usually go away if you eat or drink something that contains enough glucose, such as a glass of orange juice or some fruit.
Consuming too few calories over a longer period of time can result in serious problems, most notably malnutrition and starvation. If you are malnourished, your body is being deprived of the necessary nutrients, calories and vitamins to function, which can ultimately lead to the most severe form of malnutrition -- starvation. Symptoms of a prolonged reduction in calorie intake are similar to the milder symptoms but are more pronounced. Instead of feeling tired, for example, you feel extremely fatigued. Signs of starvation can include hair loss, lowered body temperature, severe weight loss, anemia, organ shrinkage, low blood pressure and an impaired immune system. The digestive system can also be damaged, causing chronic diarrhea and a slowing down of the metabolism. Treating starvation usually requires medical attention in addition to consuming more calories.
Not eating a balanced diet can result in long-term problems if not rectified, particularly in children and pregnant women. Children who are not properly nourished during childhood can experience stunted growth, due to their bones not receiving enough nutrients. Long-term malnutrition also affects a child's overall mental capacity and can result in permanent damage to their brain and motor control. Common problems include decreased IQ scores, learning disabilities, lack of social skills and a reduction in language skills and problem-solving abilities. Pregnant women who don't eat a balanced diet can experience symptoms of starvation more quickly. And the child she is carrying will experience problems as well, such as low birth weight and an earlier onset of chronic degenerative diseases later in life. Childhood mortality is commonly due to malnutrition, particularly in undeveloped countries.