The use of stable isotope techniques for nutritional and metabolic research in paediatrics

Stable isotope methods are increasingly used in paediatrics for clinical di agnosis and research due to marked improvements in analytical technologies and better availability of suitable tracers. The safety of stable isotopes is of major importance for use in children. Large amounts of deuterium well above the doses applied under clinical conditions may induce adverse effec ts. In contrast, heavier stable isotopes such as C-13, N-15 or O-18 do not induce adverse effects even at the highest enrichments obtained, and they a re safe. Breath tests with measurements of (CO2)-C-13 enrichment after oral application of a tracer can reliably evaluate helicobacter pylori infectio n and gastric emptying kinetics. Combined with an estimation of total CO2 p roduction, (CO2)-C-13 breath tests allow estimation of the absorption and o xidation of C-13-labelled substrates, such as medium- and long-chain trigly cerides, and demonstrates the beneficial effect of carnitine supplements on fat oxidation in primary carnitine deficiency. The study of metabolic proc esses may require the sampling of blood for isotopic analyses of metabolite s of the applied tracer. Gas chromatography-isotope ratio mass spectrometry can detect tracer in individual components from small plasma samples. The high precision enabled us to utilize the small differences in natural C-13- enrichment between dietary fats to study fatty acid turnover in term infant s, in whom the dietary fat source was switched to corn oil with a slightly higher C-13-content. With this approach we demonstrated active conversion o f linoleic into arachidonic acid. We also applied biotechnologically produc ed, U-C-13 labelled linoleic and cu-linolenic acids to infants and detected the conversion of these essential fatty acids to their longer chain polyun saturated derivatives, with an apparent change of conversion activity with age. Moreover, it has become possible to measure tissue protein synthesis f rom small biopsy samples obtained in situ without surgery, such as forceps biopsies of rectal tumors. These few examples of recent developments demons trate the great clinical and scientific potential of stable isotope methods in future paediatric applications. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.