Zinc and digestibility, Factors determining the absorption of zinc from food and food supplements
Zinc is a mineral, especially valuable for all those who are actively involved in sports. This material is useful for both advanced fitness enthusiasts and bodybuilding professionals seeking to expand their awareness in the fields of sports nutrition and nutritional supplements.
As we have pointed out in other articles (Zinc + magnesium = zma, Trace elements – chemical molecules of health), zinc (Zn) plays a very important role in our body, so it is good to know how it is absorbed. The amount of zinc absorbed in our body is that part of the total amount of zinc ingested through food or food supplements, which is retained in the body and is used for various physiological functions. The absorption of zinc by healthy people is determined by three factors:
-
the zinc content in the body;
-
the content of zinc in the food intake;
-
from the presence of soluble zinc from the components of the food intake.
The absorption of zinc in the intestine is determined mainly by its solubility there, and the solubility itself – by the chemical form of zinc and the presence of specific inhibitors or activators of zinc absorption.
Table of Contents
Factors determining the digestibility of zinc
In general, zinc is absorbed in the small intestine more efficiently by fluids in the absence of food, as well as by animal products.
Phytate (myoinositol six-phosphate), which is found in plant products and especially in cereals and legumes, irreversibly binds zinc in the small intestine and is the reason for the low absorption of zinc from plant foods. The negative effect on absorption is caused by inositol (six-phosphates and five-phosphates). Phytates with a smaller number of phosphate groups have a lower or no negative effect on calcium absorption.
When certain foods ferment (such as bread made with yeast), the fermenting microorganisms produce phytases – enzymes that break down phytates and thus increase the amount of zinc absorbed by the foods. As phytate is the main inhibitor of zinc absorption, the phytate: zinc ratio is used as an indicator of the theoretical absorption of zinc from food by the following formula: (phytate content of a food / 660) x (zinc content of a food / 65.4)
A ratio higher than 15 indicates poor digestibility, between 5 and 15 – average, and below 5 – for good absorption of zinc from a particular food.
Calcium, on the other hand, has the property of forming insoluble (and indigestible) complexes with phytate and zinc, so in order to better predict the theoretical digestibility of zinc, the phytate: zinc ratio is multiplied by the concentration of calcium in a food. It follows from the formula that the higher it is, the lower the absorption of zinc from a food will be.
However, the interaction with calcium is complex and not all studies show that calcium further reduces the absorption of zinc once it has already interacted with phytate.
Dietary fiber also has a negative effect on zinc absorption, but the reason is usually that foods rich in fiber are also rich in phytates. The amount and source of protein in the diet also affect the absorption of zinc, as it increases linearly with the amount of protein in a single meal.
Proteins of animal origin (from beef, eggs, cheese) increase the digestibility (bioavailability) of zinc contained in plant sources, probably because the amino acids obtained by digesting animal proteins keep zinc dissolved in the small intestine. The binding of zinc to low molecular weight ligands (chelators), which can be absorbed, also leads to an increase in its digestibility. EDTA, the amino acids histidine and methionine, as well as organic acids (citrates) are used as such. Interactions with divalent cations (eg iron, copper and cadmium) with zinc in the small intestine may also reduce its absorption.
Conclusion
In order to make the most of the zinc contained in its natural sources or in food supplements, it is good to avoid the consumption of legumes such as beans, wheat and unfermented (Arabic) bread in combination with sources rich in zinc.
Sources used :
- Modern Nutrition in Health and Disease, 10th edition, Shils
- Lehninger Principles of biochemistry, 4th edition, Cox
