Does the oral zinc tolerance test measure zinc absorption?

Area of Science:

• Nutritional Science
• Human Physiology
• Trace Element Metabolism

Background:

• Accurate assessment of zinc absorption is crucial for understanding nutritional status.
• Plasma zinc concentration changes reflect zinc uptake, but food matrix effects can influence absorption kinetics.

Purpose of the Study:

• To compare radiozinc absorption and plasma zinc concentration changes after oral zinc intake in liquid versus solid meal forms.
• To investigate the influence of food binding and gastric emptying on zinc absorption and plasma appearance.

Main Methods:

• Healthy subjects received oral test doses of zinc chloride (labeled with 65Zn) in water or with minced turkey.
• Plasma zinc concentrations were measured hourly for 5 hours.
• Radiozinc absorption was determined by stool counting, and retention by whole-body counting at 7 days.

Main Results:

• Mean radiozinc absorption and retention were identical (42%) for both liquid and solid meals.
• The increase in plasma zinc concentration up to 5 hours was significantly lower after the turkey meal compared to the zinc chloride solution.
• A good correlation was observed between plasma zinc curve area and 65Zn absorption in individual subjects.

Conclusions:

• Food binding and delayed gastric emptying from solid meals dampen plasma zinc appearance but do not affect overall zinc absorption.
• Plasma zinc response is a sensitive indicator of zinc absorption kinetics, influenced by meal composition.
• Radiozinc absorption measurements provide a reliable assessment of overall zinc bioavailability irrespective of meal form.