Though they appear at the opposite end of the spectrum, being overweight and being malnourished (and thus underweight) share characteristics in common. Primary among these shared characteristics is that both conditions increase children's risk of developing serious diseases. Both conditions can also negatively affect children's physical, emotional, and social development.
Whether a child is overweight, underweight, or of normal weight is always something that needs to be judged in context of that child's height, age and sex. In other words, older, taller children are supposed to weigh more than younger, shorter children. It does not make sense to consider weight in isolation of these other factors.
Body Mass Index (BMI) is a statistic (a calculated measurement) that summarizes children's height and weight in the context of their age and sex. Doctor can measure children's BMI in the office. Alternatively, online children's BMI calculators are available that can compute BMI based on children's height, weight, age and sex. The BMI number can be used to classify children into categories including 'underweight', 'healthy weight', 'at risk for being overweight', and 'overweight'. According to USA government measures, almost 20% of contemporary American children ages 6 to 11 are currently considered to be overweight! Children who fall into the 'underweight', 'at risk of being overweight', or 'overweight' BMI categories should consult with their doctor to rule out weight loss or gain due to medical problems.
Typically, children's obesity is not caused by a medical problem, but rather by excessive consumption of food (especially "junk" foods, "fast" foods and snack foods which are high in fat and refined sugar)in combination with too little exercise. Parents of overweight or near-overweight children should carefully consider what their children are eating and how active (or inactive) they are, and make changes as necessary to provide their children with more nutritious meals and more incentives for physical activity. A weight management program or visit with a nutritionist may be useful to help put new eating and activity habits in place.
Where overweight children are taking in too many calories, underweight children are not taking in enough calories to sustain them. This may occur due to poverty and the inability of the family to obtain nutritious food, to abuse or neglect, or due to children having a poor appetite due to medical or psychological concerns. Some children may suffer with depression or anxiety problems which suppress their appetite, or may be overly picky eaters who are averse to trying new foods.
Malnourishment is associated with the 'underweight' BMI categorization, but it is also possible to present at a normal weight and still be malnourished. Children at the appropriate weight for their age and sex may still be malnourished if they are not receiving appropriate levels of fiber, protein, vitamins and minerals in their diet (e.g., if they eat mostly fat, sugar, and empty calories due to the ready availability of junk food and fast food in their home).
Malnourishment takes a toll on children's health. In the short term, malnourished children will often present with weakened immune systems, as their bodies do not have the nutrients they need to maintain a strong defense against infections, cold, and flu. Additionally, they may struggle to maintain concentration, be irritable and experience mood swings. Chronic malnourishment can have lasting negative effects on children's physical and mental development.
Though not the case in all circumstances, children's obesity or malnutrition are frequently associated with lifestyle factors including poor diet and inadequate exercise. To the extent that these lifestyle factors can be corrected, children will tend to lose or gain weight so as to move towards the 'normal' weight BMI category. As well, their long and short term health risks are lowered. It is far better to reduce risks and avoid serious diseases from occurring in the first place, than to treat diseases after they have developed. Basic information concerning healthy diet and exercise can be found in earlier sections of this document, and in our Nutrition topic center.