Dear Doctor,

Are there people who can’t grow fat no matter what they eat or how bad their lifestyle is? Melisa

Dear Mellisa,

The human body is as variable as there are number of humans in this world. Tall, short, thin, fat, e.t.c. so many types of people have variations in their body structure, colour and so many other external features, depending on genetics and life style factors. Whether a person is thin or not cannot be based on the external appearance. It is determined by the BMI (basal metabolic index). This is calculated using weight and height-Weight in Kilogram/height square meters gives the value of BMI. A result>25 suggests obesity,<18 suggests being underweight and between 18 to 25 is considered normal.

A person may look underweight, but if BMI is normal, it means he/she is normal. If he is really underweight, the reasons should be probed. A low protein, low fat and carbohydrate diet can make a person underweight and look thin, because the body is deprived of necessary calories and proteins necessary to build up muscle mass and fat deposits.

Malabsorption syndrome is a group of conditions, where one does take necessary nutrients, but body fails to absorb them, causing chronic weight loss. This can also happen due to diseases of intestines, where intestines fail to absorb nutrients. Tuberculosis, cancer of the intestines are such conditions.

Loss of weight or not putting on weight can be due to an overactive thyroid gland as well. It can be known by a simple blood test that measures thyroid function tests. It is a treatable condition. Uncontrolled diabetes can also lead to weight loss, in spite of the person eating well. It may be the first sign of diabetes. It is advisable to exclude these conditions by investigations. The amount of proteins, fats and carbohydrates can be increased in the diet. If help of a dietitian can be available, he can help to tell the amount of calories to be consumed and through what types of food items, it can be available. Amount of calories necessary is worked out depending on gender, height, weight of a person and level of physical activity done.