Establishing a strong nutritional foundation during the first two years of life has been globally recognized by experts as a priority to ensure optimal growth, functional development and health later on in life. A proven indicator of nutritional health is body composition, which refers to the relative amounts of fat and lean tissue that make up the body.
A study supported by the IAEA has used a nuclear isotopic technique as well as other methods, to assess body composition in infancy and generate new international reference data. The study was recently published in the American Journal of Clinical Nutrition. Through the use of the stable isotope technique - deuterium dilution - researchers gathered body composition data from Africa, Asia, Oceania and South America, where data on nutritional status during infancy was previously based only on body proportions, such as weight and length.
"While length and weight are core components of early childhood measurements, these measurements do not provide information on a child's body composition, in other words, the fat and fat-free mass," said Alexia Alford, Nutrition Specialist at the IAEA and corresponding author of the recent infant body composition study. "The amount of fat or fat-free mass a person has, has important implications for long term health, so it is important to measure body composition during childhood."
The study, carried out between 2013 and 2019, measured body composition over the first two years of life in 1496 infants. The data collected on healthy infants represents the most diverse collection available of body composition data and has enabled international body composition reference charts to be developed for infants between birth and 24 months of age.
"These reference body composition charts will give clinicians and researchers the tool to interpret infant body composition data, which can inform and evaluate interventions to combat the double burden of malnutrition and set up healthier childhood trajectories," Alford added. The double burden of malnutrition refers to the prevalence, especially in low- and middle-income countries, of high levels of undernutrition alongside increasing obesity levels.
A better understanding of body composition in infancy can support the development of nutrition intervention strategies to curb issues related to poor overall nutritional health. An infant with poor body composition is at a higher risk of developing obesity and related non-communicable diseases, such as type 2 diabetes or heart disease, as an adult.
The new body composition reference charts will support the design of nutrition interventions based on more accurate, informative and relevant data. "In this way, the data can contribute to enhancing nutrition programmes and strengthening the global efforts to prevent malnutrition in infants and young children and related longer term poor health into adulthood," Alford said.
How nuclear techniques are used to assess body composition in infants
Looked at simply, a person's body weight comprises fat mass and fat-free mass, their body composition. Fat-free mass is composed of water, mineral and proteins, and it is assumed that fat mass contains no water. Total body water can be measured by the nuclear stable isotope technique of deuterium dilution, and when we know total body water, which corresponds to the fat-free mass, we can estimate fat mass.
Deuterium is a stable and therefore non-radioactive isotope of hydrogen, one of the two components of water (H2O). Deuterium dilution was used in this study to assess the body composition of infants between 3 and 24 months of age. A saliva sample was collected from the infant using a cotton swap before a small dose of deuterium-labelled water (2H2O) was swallowed by the infant. The labelled water then mixed with the water in the infant's body, and after a couple of hours, the isotope was evenly spread throughout the water in the body. A second saliva sample was then collected from the infant. The enrichment of deuterium in saliva was measured using isotope ratio mass spectrometry, or Fourier Transform Infrared Spectrometry. Total body water was calculated from the measured isotope enrichment and the weight and enrichment of the deuterium-labelled water consumed. From this the fat-free mass was estimated using an appropriate hydration factor. The fat mass was calculated as the difference between body weight and fat-free mass. Based on these assessments, reference charts for infant body composition, fat-free mass and fat mass, were generated.
