Using stable isotope techniques in nutrition assessments and tracking of global targets post-2015

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Conference on 'Nutrition dynamics in Africa: opportunities and challenges for meeting the sustainable development goals'

9-14 October 2016

7th Africa Nutritional Epidemiology Conference (ANEC VII)

Palm Plaza Hotel, Marrakech

Isotopes are elements with identical chemical and functional properties but different in atomic mass due to having different number of neutrons in the nucleus. The difference in mass makes it possible for the isotopes to be analytically set apart from each other⁽¹⁾. Thus the metabolic fate of each isotope can be traced when introduced into a biological system. Stable isotopes refer to non-radioactive isotopes occurring naturally, but elements or compounds can be synthesised that are enriched compared with the naturally occurring amount. Stable isotope techniques have been used in studies of human nutrition for over 50 years⁽²⁾. With the development of MS and infrared spectroscopy techniques coupled with wide commercial availability of tracers labelled with stable isotopes including¹³C,¹⁵N,²H and¹⁸O, detailed metabolic pathways can be investigated⁽³⁾.

In nutrition, stable isotopes can be used to measure the amount of water or other nutrients in the body or the amount of an ingested nutrient that is absorbed and metabolised or excreted. They can be applied to determine the rate of absorption, utilisation or synthesis of proteins, fats or carbohydrates. Stable isotope techniques are non-invasive, and do not involve any radiation hazard. In nutritional assessments, stable isotope labelled compounds are given orally, often as part of a test meal, or intravenously and after a period of time urine, saliva, blood or breath samples are collected and the enrichment of the administered isotope in the compound of interest is measured using MS or infrared spectroscopy techniques.

Application of stable isotopes in nutrition assessments

Examples of applications of stable isotope techniques of relevance to the public health agenda include: assessment of breast-feeding practices, body composition, energy expenditure and energy requirements, evaluation of food-based approaches to improve nutrient intake, assessment of nutrient bioavailability and gut function. The first three of these involve the use of labelled water. Water is composed of isotopes of hydrogen and oxygen. Natural water is composed mainly of¹