In clinical research, area under the curve (AUC) is defined as the integral of the concentration of a substance in the blood over time.

In more practical terms, AUC allows researchers to look at how the concentration of a substance in the blood changes, and use that information to calculate the total amount of the substance that was present in the blood over the whole measurement period.

There are two uses of AUC that are especially common in nutrition research:

1. Determining bioavailability: Just because you consume a supplement doesn’t necessarily mean it’ll all end up in your body — the processing of substances and their chemical characteristics can dramatically alter how easily they’re absorbed and whether it’s metabolized by the liver before entering the bloodstream. If a participant consumes a known amount of a substance, then measuring the concentration of that substance in the blood and calculating the AUC represents how much of the substance actually made it into the blood.
2. Measuring glycemic response: Insulin is required to transport glucose from our blood into many of the tissues in our bodies (where it’s actually used for energy). Broadly speaking, it’s considered better for blood sugar to remain relatively low after a meal, which is achieved by the release of an appropriate amount of insulin into the bloodstream. Ideally, only a small amount of insulin is required to achieve this effect; if someone requires large amounts of insulin they may be considered to be “insulin resistant”. In a clinical setting, researchers can track how the concentrations of glucose and insulin in their blood change over time, and then compute their AUC to evaluate how much total glucose and insulin was present in their blood during the measurement period.