The International Symposium on Understanding the Double Burden of Malnutrition for Effective Interventions was held at the International Atomic Energy Agency (IAEA) headquarters in Vienna, Austria, from 10 to 13 December 2018. The Symposium was hosted by the IAEA in cooperation with the World Health Organization and United Nations Children's Fund. The double burden of malnutrition (DBM) is a complex situation characterised by the co‐existence of overweight/obesity, underweight and/or undernutrition, and can occur at the individual, household and population levels across the lifespan. Currently, one in three individuals worldwide suffer from at least one form of malnutrition. The objective of the meeting was to strengthen understanding of how to tackle the DBM by sharing research findings, ideas and issues with the implementation of relevant interventions, programmes and policies. In particular, the Symposium highlighted the crucial roles stable isotopes play in the assessment and monitoring of the DBM and in measuring the impact of programmes designed to address this issue. The range of stable isotope applications considered at the meeting is discussed in this paper and includes the assessment of body composition, total energy expenditure, breastfeeding practices and micronutrient bioavailability.