CRP Success Story: Novel Stable Isotope Method Reveals Pathways for Nutrient Absorption

Despite EED’s prevalence and impact on health and well-being, the dysfunction is difficult to diagnose definitively since the gold standard for doing so involves an intestinal biopsy to determine gut damage. However, such an invasive clinical procedure is not feasible in community settings, especially in low-resource areas. Another approach, the dual-sugar test – which involves consuming sugars of different sizes (for example, lactulose and rhamnose) to see if there is an increased appearance of the larger one in urine –gives widely varying results. Breath tests utilizing carbon-13-labelled carbon dioxide cannot assess intestinal structure or permeability changes, but they can help in understanding general nutrient malabsorption – one of the effects of EED.

In bringing together nine countries, an IAEA coordinated research project (CRP E41016) aimed to validate and apply a novel, non-invasive stable isotope technique to foster better understanding of the pathways underpinning EED and child growth. Specific objectives included:

• Developing a protocol with highly enriched carbon-13-labelled sucrose, which was used to diagnose EED in adults in the United Kingdom.
• Validating the newly optimized protocol by comparing it to intestinal biopsy and sucrase activity, which was carried out among Zambian adults.
• Testing its applicability in diagnosing EED compared to the lactulose: rhamnose test, while also exploring the link to child growth in countries such as Bangladesh, India, Jamaica, Kenya, Peru and Zambia.
• Applying mathematical modelling to further explain the biological pathways underpinning intestinal sucrose absorption.

The main study involved a total of 158 children aged 12 to 15 months, who were measured using the carbon-13 sucrose breath test (SBT). A baseline breath sample was collected prior to receiving an oral dose of carbon-13 sucrose, with subsequent samples collected every 15 minutes for the first 90 minutes, and additional samples taken every 30 minutes for the next 150 minutes. Laboratories in Australia, India, and the United Kingdom analysed carbon-13-labelled carbon dioxide ratios in these samples as an indication of intestinal absorptive capacity. Children also underwent the dual-sugar test, and a laboratory in the United States of America analysed their urine samples to measure intestinal leakiness.

The timing of the sample collection was crucial as it helped identify the pattern of nutrient absorption and the rate at which carbon-13 sucrose was metabolized, providing key insights into the children’s ability to absorb nutrients.

A separate study in Australia, whose results are yet to be analyzed, compared carbon-13-SBT to intestinal biopsy for children with coeliac disease. This comparison is important because coeliac disease is a condition that manifests in a similar fashion to EED, providing a benchmark for understanding the potential broader applicability of the test.

In optimizing carbon-13-SBT, the CRP has provided countries around the world with an easy-to-perform tool for assessing nutrient absorption in the context of EED. While the test itself is not directly linked to intestinal structure nor leakiness (and therefore could not be validated against intestinal biopsy), the technique is nevertheless strongly related to the enzymatic processes involved in breaking down sucrose for absorption. Findings also reveal that carbon-13-labelled carbon dioxide recovery was not directly linked to child growth. This is likely because growth is influenced by multiple factors beyond nutrient absorption, such as immune function, environmental conditions, and overall health status. Subject to further research, the test could potentially be used to explore sucrase activity in other related conditions affecting nutrient digestion, such as severe acute malnutrition associated with disrupted pancreatic or liver function.

Beyond fostering North-South and South-South collaboration and facilitating the training of postgraduate as well as doctoral students, the CRP has inspired other research activities. For example, scientists in the Philippines are applying carbon-13-SBT to explore links between EED and stunting as part of a technical cooperation project. For its part, the IAEA has launched additional CRPs to assess the efficacy of amino acid supplementation in treating EED symptoms and measure added sugar intake in the context of the obesity pandemic, where the carbon-13 sucrose breath test is being used.

With the link between adverse environmental exposures and stunting yet to be fully understood, the IAEA’s CRP helps unlock the metabolic workings of the human body – bringing the world one step closer to tackling a pressing global health challenge.