The World Health Organization (WHO) defines malnutrition as the cellular imbalance between the supply of nutrients and energy and the body’s demand for them to ensure growth, maintenance, and specific functions.
Malnutrition generally implies undernutrition and refers to all deviations from adequate and optimal nutritional status in infants, children and in adults. In children, undernutrition manifests as underweight and stunting (short stature), while severely undernourished children present with the symptoms and signs that characterize conditions known as kwashiorkor, marasmus or marasmic-kwashiorkor.
BMI is body weight divided by a power of height, usually (height)2, which is said to be independent of stature. Calculations based on values for ideal body weight suggest that BMIs for normal men and women should be in the range of 18.5 to 25 kg/m2. Indeed, this range roughly corresponds to the 10th to 75th percentile values recorded from adult individuals. For infants and children, average BMI values change with age, from 13 kg/m2 at birth, to a peak of 18 at about 1 year, a nadir of 15 at about age 6 years, and then a rise to adult values during adolescence.