Underweight, like overweight, is a relative term, being based on the ideal weight for a given height, build and sex. A person can be regarded as moderately underweight if he or she weighs 10 per cent below the ideal body weight and markedly so if 20 per cent below the ideal.
Approximate body weight is among the most important physical attributes and has a deep influence upon the health and personality of an individual. For a healthy body, weight slightly above the average is favourable upto the age of 30 years, as it serves as a good defence measure against certain diseases, especially tuberculosis, which are widely prevalent among the adolescent and the young.
Between 30 and 40 years of age, weight should be maintained at the average level as during this period, many future diseases have their beginning. After the age of 40, it will be advisable to keep the weight slightly below the average, so as to lighten the burden on the heart, kidneys and other vital organs.
There are two types of thin people. One type is wiry and energetic, who eat heartily but never put on weight. Presumably, they burn up energy due to constant activity. Such persons need not worry as chances are that they do not have any disease as such.
The other type of thin persons lack energy and drive, are unable to take normal meals and find that rich food usually makes them sick. Their body lacks fat cells thus providing no storage place for added fat and the calories they consume are probably wasted.
Symptoms
Underweight due to an inadequate calorie intake is a serious condition, especially in the young. They often feel easily fatigued, have poor physical stamina and lowered resistance to infection. Diseases like tuberculosis, respiratory disorders, pneumonia, circulatory diseases like heart disorders, cerebral haemorrhage, nepthritis, typhoid fever and cancer are quite common among them. The occurrence of the complications of pregnancy in young women may result from malnutrition due to an inadequate energy intake.
Causes
Thinness may be due to inadequate nutrition or excessive bodily activity or both. Emotional factors or bad habits such as skipped meals, small meals, habitual fasting and inadequate exercise are some of the other causes of thinness. Other factors include inadequate digestion and absorption of food due to a wrong dietary pattern for a particular metabolism; metabolic disturbances such as an overactive thyroid and hereditary tendencies.
Disorders such as chronic dyspepsia, chronic diarrhoea, presence of parasites like tapeworm in the ailmentary canal, liver disorders, diabetes mellitus, insomnia, constipation and sexual disorders can also lead to thinness.
It has been observed that most underweight persons are not healthy. They are usually tense and lack appetite. Eating large quantities of food will not help them to gain weight until and unless their health improves. They can gain weight only when these abnormalities are overcome. Building up their health is, therefore, of utmost importance.