The primary factors that decrease protein absorption are the size and charge of the protein molecules.
Why Size and Charge Matter
According to research, protein absorption is primarily limited by the ability of protein molecules to pass through the cellular lipid bilayer membrane. This membrane acts as a barrier, specifically impeding the passage of:
- Large Molecules: Proteins are large molecules, and the larger they are, the more difficult they are to absorb.
- Hydrophilic (Water-Loving) Molecules: Proteins are generally hydrophilic. This characteristic makes it hard for them to move through the lipid membrane because it's lipophilic (fat-loving).
- Charged Molecules: The charge of a protein molecule also makes it harder to pass through the lipid membrane because the membrane is non-polar.
How These Barriers Affect Absorption
Here's a breakdown of how these barriers impact the absorption of proteins:
- Size: Large, intact protein molecules struggle to pass through the intestinal lining. This is why proteins are typically broken down into smaller peptides and amino acids before absorption.
- Charge: The positive or negative charge on a protein can hinder its passage through the cell membrane.
- Hydrophilicity: Water-loving (hydrophilic) molecules like proteins struggle to cross the lipid bilayer, which is a fat-loving (lipophilic) barrier.
Practical Implications
These limitations influence how the body processes proteins:
- Digestion: The body has developed digestive processes (enzymes) that break down large proteins into smaller, absorbable peptides and amino acids.
- Absorption Mechanisms: The intestinal cells employ transporters that help carry the resulting small peptides and amino acids through the cell membrane and into the bloodstream.
- Efficiency: While the body is designed to handle protein digestion and absorption, factors that impede these processes (such as large protein size, charge, and hydrophilicity) can reduce overall absorption efficiency.
In summary, it is the physical properties of protein molecules such as size and charge that primarily hinder the absorption process. The body uses methods to breakdown large molecules into smaller, absorbable units to counter these limitations.
