2.2.2. Inhibitors of nutrient bioavailability

Inhibitors are substances that reduce the bioavailability of a nutrient, we also call these anti-nutrients. Inhibitors may reduce nutrient bioavailability by: 1. binding the nutrient in a form that is not recognized by the uptake systems on the surface of intestinal cells, 2. making the nutrient insoluble and thus unavailable for absorption, or 3. competing for the same uptake system (EUFIC). Phytic acid (or phytate) is highly abundant in certain plant foods (e.g. nuts, pulses, whole-grain cereals, seeds in general) and strongly binds minerals such as calcium, iron and zinc, thus lowering their availability for absorption (Zhou et al. 1995). Phytic acid content of foods can be reduced through fermentation or by soaking and germination of pulses.

An example of competition for the same uptake system is the interaction between non-haem iron and calcium. Both cations bind to a transporter on the surface of intestinal absorptive cells, but whereas non-haem iron enters the cells in this manner, calcium basically stays in the doorway and hinders further entry of the iron molecules (EUFIC)

The inhibitory effect of food constituents can also be used in favour of nutrition, as is done in the case of phytosterols. These natural compounds are extracted from certain plant foods and added in relative high doses to various other food products (e.g. margarine spreads) in order to lower the absorption of cholesterol either from other dietary sources or produced in the human body (EUFIC).