The mixed-meal tolerance test as an appetite assay: methodological and practical considerations

Appetite control is a topic which attracts widespread interest given its importance to energy balance and obesity. In this research area, the mixed-meal tolerance test (MM-TT) has emerged as an 'appetite regulation assay', facilitating the dynamic assessment of appetite parameters (e.g. subjective appetite perceptions, appetite-related hormones, food reward) in response to an individual meal. The MM-TT is commonly employed in observational and experimental studies to examine population differences and intervention effects. Problematically, no practice standard exists for the MM-TT and protocols vary widely. This presents a challenge for researchers designing new MM-TTs and hampers the comparability of findings. Therefore, within this narrative review we sought to identify and discuss key methodological considerations inherent within a MM-TT. The scope of our review extends to evaluating participant familiarisation and methodological standardisation practices, test meal characteristics, appetite perception assessment, blood sampling techniques, measurement of appetite-related hormones and data handling/analysis. A checklist has been devised to summarise relevant methodological issues identified within this review. This checklist can be used as a tool by researchers to facilitate MM-TT design and promote greater standardisation/comparability between studies. This review highlights the need for broader standardisation of MM-TT procedures to support consistency across future research. Additional research is needed to strengthen the evidence base on which various recommendations are made, particularly relating to participant familiarisation and methodological standardisation practices. Additional scrutiny of less common outcomes employed in MM-TTs (not addressed here), such as diet-induced thermogenesis, gastric emptying and ad libitum energy intake, is also needed.