Dietary reference values (DRV) are estimates of the daily amounts of nutrients or food energy that meet the needs of healthy people. In the UK, three terms are used to express these estimates, assuming a normal distribution of requirements in a population. These are the estimated average requirement, the lower reference nutrient intake and the reference nutrient intake. DRV are for use in a variety of settings, including the assessment of adequacy and safety of nutrient or energy intake in a population group, in the design of meal provision in care settings, in food labelling and in considering food fortification strategies. DRV, and other expressions of nutrient requirements, assume a relationship between the intake of a nutrient and some criterion of adequacy, the outcome. Estimates of requirements are based on a diverse range of measures of adequacy, according to available evidence. The Scientific Advisory Committee on Nutrition (SACN) is the body responsible for reviewing and setting DRV for the UK population. The work of SACN is guided by a framework of evidence that relates food and nutrients to health. There have been calls for the harmonisation of approaches used in the setting of nutrient requirements, globally, and an increased transparency in the decision-making process. Some progress has been made in this regard, but there is a great deal of work to be done.

Policy decisions and the practice of public health nutrition need to be based on solid evidence, developed through rigorous research studies where objective measures are used and results that run counter to dogma are not dismissed but investigated. In recent years, enhancements in study designs, and methodologies for systematic reviews and meta-analysis, have improved the evidence-base for nutrition policy and practice. However, these still rely on a full appreciation of the strengths and limitations of the measures on which conclusions are drawn and on the thorough investigation of outcomes that do not fit expectations or prevailing convictions. The importance of ‘hard facts’ and ‘misfits’ in research designed to advance knowledge and improve public health nutrition is illustrated in this paper through a selection of studies from different stages in my research career, focused on the nutritional requirements of resource-poor populations in Africa and Asia.

All human tissues are in a constant state of remodelling, regulated by the balance between tissue protein synthesis and breakdown rates. It has been well-established that protein ingestion stimulates skeletal muscle and whole-body protein synthesis. Stable isotope-labelled amino acid methodologies are commonly applied to assess the various aspects of protein metabolism in vivo in human subjects. However, to achieve a more comprehensive assessment of post-prandial protein handling in vivo in human subjects, intravenous stable isotope-labelled amino acid infusions can be combined with the ingestion of intrinsically labelled protein and the collection of blood and muscle tissue samples. The combined application of ingesting intrinsically labelled protein with continuous intravenous stable isotope-labelled amino acid infusion allows the simultaneous assessment of protein digestion and amino acid absorption kinetics (e.g. release of dietary protein-derived amino acids into the circulation), whole-body protein metabolism (whole-body protein synthesis, breakdown and oxidation rates and net protein balance) and skeletal muscle metabolism (muscle protein fractional synthesis rates and dietary protein-derived amino acid incorporation into muscle protein). The purpose of this review is to provide an overview of the various aspects of post-prandial protein handling and metabolism with a focus on insights obtained from studies that have applied intrinsically labelled protein under a variety of conditions in different populations.