GLOSSARY

Amino Acid and Peptide Transporters Table

Amino acids and small peptides use multiple intestinal transport systems with differing substrate specificity.

Peptide Transporter 1 (PEPT1) imports small peptides through proton coupling, distinct from simple-sugar transport.

Amino acids enter through several carrier families, while dipeptides and tripeptides use proton-coupled peptide transport. Many small peptides are hydrolyzed within enterocytes before amino acids enter portal blood. Ordinary dietary protein uptake does not mean large-scale passage of intact whole proteins into circulation. Tolerance, quality and quantity remain relevant to sports protein selection alongside these mechanisms, and faster uptake alone does not define the better daily diet.

Acid and pepsin initiate gastric protein processing, followed by pancreatic proteases and intestinal peptidases. Endopeptidases attack internal bonds; exopeptidases work at chain ends. Products include small peptides as well as free amino acids. A hydrolyzed powder does not automatically provide complete uptake, superior muscle growth or a requirement for every athlete. Total protein, quality and meal planning still matter beyond the speed of one digestive step.

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.

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.

For a sports product, separate the pathway's normal role from package claims; assess actual composition, amount and training tolerance rather than treating an enzyme name as a reason to buy or consume more.

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.

For sports use, consider meal size and timing together with fluids, intensity and composition. Large, fiber-rich or fatty meals close to exercise trouble some individuals, but tolerance varies. Changing one factor during training and recording responses helps identify patterns. First-time competition products or broad food exclusions without a replacement plan do not substitute for this practical evaluation and can compromise adequate fueling.

Table references: NIDDK · 1