Endocronologist (Pediatric) Questions Underweight

Why is my son not gaining weight?

My son is 15 years old and is still underweight. He eats normally and isn't exactly active. Why is he not gaining any weight?

5 Answers

Male teenagers underweight need a full history and physical exam as well as some exploratory lab testing. Possibilities include overactive thyroid, underactive adrenal gland, hypopituitary problems as well as a long list of gastrointestinal problems such as celiac disease, Crohn's, ulcerative colitis and psychological difficulties including eating disorders. If here is something positive on detailed history or examination, that may provide some clues to pursue but first one needs current weight and height plotted
He may be experiencing a growth spurt, the weight coming later.
Many possible reasons. GI Tract could be malabsorbing calories, metabolic rate could be high (overactive thyroid), early onset of diabetes (increased thirst and urination), eating disorder, side effect of a new medication (ADHD meds, for example). These are a good start to consider, but there are others and they would be driven by a careful medical history.
Thinness or failure to thrive could be due to inadequate weight gain or inappropriate weight loss. These conditions may be due to poor appetite, poor calorie intake, malabsorption or excessive calorie expenditure.
Many children with poor appetite due to various reasons, may have failure to thrive. Failure to thrive may also take place while appetite is normal. In this scenario the child may have either malabsorption or excessive calories expenditure. Malabsorption may be due to gastrointestinal issues such as celiac disease, lactose intolerance, protein allergy etc. And excessive calories expenditure could be due to hyperthyroid, anemia, heart disease, cystic fibrosis, diabetes and other diseases that reguire more calories expenditure. Some children who have good appetite may not gain optimum weight as these children may have constitutional underweight which is a normal variant of growth.
Most children gain weight in a predictable fashion. A new born child baby is about 7.5 pounds at birth. Birth weight is doubled at 3 months and tripled at one year. At age 5 years the average child is 40 pounds in weight. Thereafter the child (boys) gains about 5 pounds untill the age of puberty 12 years. After the age of 12 years the average child gains about 9 pounds per year until adulthood. A simple formula could be also used to calculate the weight of a child after the age of 1 year. (age x 4.4 pounds +18 pounds = average weight of a child at that age). Linear height growth also follows a predictable process. The formula for height after the age of 1 year is as follows: age x 5cm + 80 cm = the height in centimeter of the average child for that age. To covert this to inches, simply divide it by 2.54.
Children who have poor appetite and or have failure to thrive, those children whose weight is less than 20% of thier hieght or those who fell 2 or more centiles of the wieght growth curve or the ones whose weight is below the 3rd percentile, need proper evaluation by an expert. Medical, hormonal genetic, psychological and environmental factors should be ruled out.
Children who have poor appetite and those who are picky and Small eaters and those with failure to thrive need to be provided with high calorie foods. They need to eat more frequently and should always have bedtime snacks. Calories can be fortified with cheese, creams, peanut butter, butter and oil. Seeing a good nutritionist will also be very important. Nutritional consultation will help in understanding of nutritional values of different foods and micronutrients. If indicated some children can benefit from apettite stimulating agents. Cyproheptadine is commonly used for this purpose. 2-4 mg three times a day half hour before meals may help. Oxandrolone 5-10 mg can be considered for some children. Progesterone base medications ( such as megace) are reserved for serious illnesses such as cystic fibrosis and wasting syndromes. These things should be discussed with the physician if they are ever indicated. The most important thing is optimizing calorie intake.
Going back to your question: If your son have a normal linear hieght growth but his weight is low or has poor appetite, he may have a constitutional underweight which is a normal variation. But if linear hieght growth is affected, he may have more issues going on. If your son has a good appetite and is not a small or a picky eater and, his height is normal that is likely his genetic program. It is important that you have him see his doctor and have him proper evaluation and get referral if indicated. Basic work up should be performed to rule out hormonal and medical conditions. You should also see a good nutritionist to help you appreciate different foods and nutrients. You should optimize calorie intake as much as you can. Add Cheese, butter, oil etc to his food. Let him eat high calorie foods more frequently at least 6 times (three meals and three snacks) a day and remember to provide him with high calorie bedtime snacks. Ask your doctor if he can benefit from weight promoting agents if indicated. The most important thing is to work with your doctor closely.
Good luck.
Weight gain is usually a balance between caloric intake and physical activity. There are also genetic factors and hormonal factors that play important roles in weight gain. I will recommend you to seek the advice of a endocrinologist to be sure that there is no a hormonal disbalance ( for example hyperthyroidism) with your son.