Understanding human body composition in the first two years of life

A recent European Journal of Clinical Nutrition study highlights some of the historical challenges associated with the assessment of body composition in the first two years of life.

Study: Body composition from birth to 2 years. Image Credit: didesigns021 / Shutterstock.com

Background

Historically, anthropometric measurements such as height, weight, and head circumference have been used to assess the development, growth, and nutritional status of infants. This stage of life is crucial in developing phenotypic metabolic profiles that are subsequently associated with health status later in life.

Previous studies have identified associations between birth size and susceptibility to future illnesses as an adult. This suggests that the ‘quality’ of growth is a key determinant of the risk of later abnormal metabolic function.

Improving the current understanding of early life changes is important, especially considering the high prevalence of numerous cancers, cardiovascular diseases, and other diseases.

A critical window for growth and development

The first 1,000-day window from conception to two years of age is referred to as the ‘critical window’ for growth and development. Accurately assessing body composition and body growth at this stage could assist in the early identification of health risks, which could then lead to proper interventions.

Importantly, obtaining these precise measurements during fetal growth would provide important insights into the infant’s projected quality of growth after birth. The role of a healthy pregnancy also contributes to fetal growth; therefore, further studies are needed to determine the role of the mother’s body composition and health status before and during pregnancy on infant growth.

Despite existing evidence that the early phase of life is crucial, malnourishment and undernutrition are still common issues, especially in low- to middle-income countries. There is strong epidemiological evidence that individuals who are small or thin at birth experience a higher likelihood of chronic disease in adulthood.

Limitations in assessing growth and development

Despite the widespread use of anthropometric screening of height and weight, this methodology is associated with certain limitations, such as the relative proportions of lean and adipose tissue being very different for the same body weight.

At the population level, anthropometry is a useful approach to monitoring changes in physical growth; however, the lack of representation to all population groups limits its practical use. Thus, supplementing traditional size and shape measurements with data on body composition to define the quality of physical growth will improve the accuracy of these measurements.

Under healthy conditions, most of the body’s water is held within the lean tissue. Therefore, an assessment of total body water (TBW) provides an index of fat-free mass (FFM).

In a two-compartment model, fat mass (FM) can be obtained by subtracting FFM from body mass. This model is simple and versatile and continues to be used, despite the availability of three- and four-compartment approaches, which require additional technical equipment. This restricts their use to smaller sizes.

Most body composition assessment techniques cannot be applied to infants and young children, as they have only been validated in adults. As compared to adults, growth changes during infancy are quite dynamic and complex, thus increasing the complexity of obtaining their measurements.

Among recent developments, hydrometry, which is based on isotope dilution, appears to be useful for compositional assessment in infancy. This approach is easy to administer, safe, and non-radioactive.

The value of high-quality data

In a defined population at a specific point in time, normative data refers to the preferred and observed statistical statement of the distribution of characteristics. Growth assessments have typically been made on convenience samples rather than preferred samples.

The INTERGROWTH-21st Consortium and the World Health Organization (WHO) Child Growth Standards have significantly advanced current knowledge on how disease-free children should grow when exposed to standard health practices in a non-smoking environment. Overall, the availability of the first normative body composition data up to two years of age could provide deeper insights into growth and development during this critical stage of life.

Conclusions

Recently, the WHO Child Growth Standards generated from anthropometric data have been complemented with reference charts for body composition. The next step is to develop a global consensus on protocols and definitions for both body composition and anthropometry in infancy.

A shared vision between the United Nations (UN) agencies and stakeholder organizations is important for the harmonization and standardization of measurement approaches. Thus, improving quality control mechanisms and training of relevant health professionals should be encouraged.