GLOSSARY

Nutrient Uptake is entry into a specified cell or tissue, requiring distinction between enterocyte uptake and uptake by muscle or other tissues.

Diffusion follows its driving force; facilitated diffusion uses a protein without necessarily consuming energy directly. Primary active transport uses direct energy, while secondary transport uses a gradient established elsewhere. Transcellular passage differs from movement between cells. Active, saturable or carrier-mediated terminology does not imply unlimited speed or complete absorption. Identify the mechanism and substrate rather than assuming all intestinal transport requires the same energy source.

A transporter generally has substrate preferences and finite capacity, so fractional uptake may change as dose rises. Competition depends on substance, concentration and conditions; ordinary foods do not all cancel each other out. Gradual fueling practice and tolerance assessment are useful in sport. Findings from a concentrated experimental dose should not be generalized without context to a mixed meal or an athlete's whole daily diet.

Fractional absorption relates absorbed amount to a defined intake, whereas absorption rate expresses amount per time. Rates can differ despite similar final fractions, or the reverse. Specify nutrient, dose and interval when reporting percentages. A rising blood concentration also reflects more than entry because tissue removal and metabolism occur simultaneously. Neither one blood peak nor a rapid label claim establishes total absorption.