Getting the label in: practical research strategies for tracing dietary fat.

The observation that events occurring after consumption of a meal can directly affect metabolic risk has been gaining interest over the past 40 years. As a result, the desire for investigators to conduct postprandial studies has also increased. Study design decisions pertaining to the choice of meal quantity and composition are more difficult than may be readily apparent, and there is now ample evidence available in the literature to suggest that what is fed on the test day significantly affects postprandial metabolism and can therefore influence interpretation of results. In addition, events occurring before the testing day (food intake and activities) can also have an impact on the observed postprandial response. The goal of this review is to present aspects of study design critical to the investigation of postprandial metabolism. These details include subject preparation, meal quantity, form and composition, as well as sampling protocols for measuring metabolites. Key factors and practical examples are provided to minimize the impact of nonresearch variables on subject variability. Finally, aspects related to using stable isotope tracers to measure metabolism of meal fat are discussed, including choice of tracer form, dose and delivery in food. Given that fed-state events contribute significantly to chronic disease risk, improved methods to study the absorption and disposal of food energy will support the development of strategies designed to prevent and treat diseases associated with overconsumption of nutrients.