Why is IAEA helping to evaluate body composition?
Body composition as a health indicator
Meaning of `body composition'
For most public health purposes, as well as for many clinical applications, total body weight is divided conceptually into two compartments, the fat-free mass and the fat mass. The fat-free mass as a percent of body weight in healthy people ranges from 65 to 85%. Some of the variation in healthy people is due to gender, age and ethnicity. The fat-free mass is made of protein, water (about 73%) and minerals. These data form the basis of most methods for assessing body composition.
Body composition and aging
Aging is associated with changes in body composition which increase the risks of disease and accidents and limit participation in activities they once considered normal. Some changes in body composition can be prevented or reversed by exercise and diet, but planning and evaluating interventions to prevent or reverse body compositional change during aging relies on good assessment tools. Body composition measurements are ideal for this.
The health status of elderly people will be a rapidly growing concern, especially for developing countries. In 1950 there were approximately 200 million people in the world aged 60 years and over. By 2025, there will be 1.2 billion elderly people in the world, 60% of whom will reside in developing countries.
Undernutrition and body composition
Primary undernutrition alters body composition, as does secondary malnutrition (ie., malnutrition which occurs because of an underlying disease). Severely malnourished underweight children are not just scaled-down versions of normal children but differ markedly in body composition. Body composition is useful in estimating children's nutritional needs and in evaluating the success of child feeding programmes.
Overnutrition and body composition
Obesity is spiralling as a global public health problem. Obesity is not limited to technologically advanced countries but in fact is now prevalent in formerly malnourished populations in developing countries.
Obesity in children, adolescents, and adults has major impacts on health. It is a risk-factor in the development of diabetes, vision and kidney disorders, circulatory problems, and early death. Obesity can limit activity, productivity, and increase absenteeism from the workplace.
Experts are vigilantly looking for ways to prevent obesity and its untoward consequences. Body composition and energy expenditure data are major tools in this endeavour.
Energy used + energy stored = energy eaten
According to basic principles of thermodynamics, all dietary energy (calories eaten) is either utilized (expended) or is stored. The more fat one stores, the more energy one has stored. In people who are gaining or losing weight, energy stores are either increased (weight gain) or used as an energy source (weight loss). The difference between dietary energy and energy expended is equal to the total amount of energy stored. Thus, measurements of energy expenditure are very useful for determining how much energy has been stored and are indispensable to strategies for reducing the morbidity and mortality associated with undesirable changes in body composition. Additionally energy expenditure measurements are useful for measuring food intake and energy needs under conditions of pregnancy, lactation, growth and aging.
Energy expenditure data can be used to:
Measuring body composition and energy expenditure (EE): conventional indicators and isotopic techniques
There are many techniques for measuring body composition (skinfold thicknesses, neutron activation, densitometry, infrared interactance, electrical conductance, 2H or 18O dilution, computer tomography). Selection of a method depends on one's objectives, cost limitations, precision and accuracy required and on the convenience and health of the subject.
The method which is often preferred is isotope dilution (2H or 18O) because it is inexpensive to perform, accurate, practical, can be applied under field conditions and poses no risk or discomfort to the person measured.
To measure body composition, body water is measured by giving a dose of water labelled with either deuterium (2H) or 18O. Isotope enrichment, measured in urine samples, is a function of the amount of body water. Body composition is calculated from measured body water and the hydration coefficient of the fat-free mass. Fat is calculated as the difference between total body weight and fat-free mass.
There are no alternatives to the isotopic methods for measuring EE in everyday living conditions. The doubly-labelled water (DLW) method (2H218O) is the only technique that can accurately determine the energy needs of people in their own environments and is one of the most reliable methods for determining food energy intake.
IAEA'S role in investigating body composition
The IAEA has helped develop and apply methods for measuring body composition. For example, measurements of body composition helped define nutritional treatments which sped recovery of undernourished children, and helped identify local foods and diets which can provide the specific nutrients children need for growth.
There is a growing consensus among global nutrition experts that evaluating body composition in children and adults will improve national health profiles -an important step in targeting health and nutrition interventions. Moreover, isotopic tools increase the reliability of reference growth charts used in monitoring children in developing countries. This is important because current standards are based on observations of healthy children in industrialized countries, and can be misleading for children in developing countries. Several Member States have already indicated their interest in such activities.
Recovering from malnutrition: lessons from Peru
Almost half of all schoolchildren in Peru are stunted as a result of chronic nutrient deficiencies and frequent bouts of diarrhoeal diseases. As youngsters, they were likely to suffer in many ways: from underweight, lower disease resistance, lethargy, and learning handicaps. Only by addressing this early and thoroughly through specially formulated diets could such a costly outcome be avoided.
Healthy infants gain 1 to 2 grams per kg per day. Rapid weight gain of as much as 160 grams per day in an 8 kg child is biologically possible and can substantially reduce the time needed for recovery. During the rapid catch-up weight gain period, children have enormous appetites; once their weight is restored to that which is typical for their age, appetite declines.
The challenges are to know how much of each essential nutrient to provide to enable children to achieve their potentials for growth, cognitive development, and physical activity. Body composition is an indicator of the kind of nutritional deficiencies which need restitution, and can be used to assess the progress of recovery. Body composition assessment is therefore a tool which helps define nutrient needs under these special conditions.
Conventional methods cannot be relied upon to quantify actual changes in body composition. But using isotopic methods to evaluate dietary energy utilization and body composition changes, the Agency, in collaboration with the Instituto de Investigación Nutricionál (IIN) in Lima, Peru, were able to demonstrate that diets amply fortified with micronutrients during the catch-up phase result in the use of dietary energy to adequately meet all needs, including those for rapid weight gain with a typical ratio of muscle to fat. The results of the work meant that children following the prescribed dietary treatment could be fully recovered to normal weight in about 50% of the time which was needed previously.