Importance of consuming a combination of Maltodextrin & Dextrose
Beginning with the first concept discussed called, “gastric emptying.” Our goal post workout is to maintain a prompt digestion rate so nutrients can transport swiftly and efficiently to our muscles. With that said, it has been shown that this process slows when the ingested fluid contains a high osmolarity concentration (the second concept studied). Osmolarity is dependent on the number of particles in a solution. That is, a100-milliliter solution with 20 glucose molecules will have a higher osmolarity then a100-millileter solution that only contains 10 molecules. The shorter chain length a carbohydrate has, the higher it raises the solution's osmolarity. Therefore, it is no surprise that a pure glucose solution (or dextrose, a monosaccharide) induces very high concentrations of solute (1,3,10).
Fortunately these negative effects become greatly reduced when the drink contains a glucose polymer stacked with dextrose. However, a carbohydrate that is easily digested, and has a high Gl is still desired. Hence, a combination of dextrose and maltodextrin is advised. Osmolarity will be decreased, and glucose will still enter the blood stream at a proficient rate, thus maintaining its anabolic nature (1,3).
A second factor concerning osmolarity must now be examined. From a clinical standpoint, it is vital to take into consideration the fact that plasma (the liquid portion of blood) has an Osmolarity of 300 mOsm. This means that if one were to inject a solution with a greater concentration of solute into their blood, it would cause water from inside their red blood cells to leave by Osmosis (water always travels down its concentration gradient) and move into the plasma, in turn shrinking the erythrocytes (red blood cells). This is because the cells are iso-osmotic to the plasma (both have the same concentration of solute) (11).
A similar concept can be applied to your post workout meal. If a competitor were to consume a solution that was hypertonic or had a higher concentration of solute then 300 mOsm, it could dehydrate them (showing why digestion is rightfully slowed in a high concentrated solution). The addition of maltodextrin once again solves this problem (2,13).
The next question is, why not just use maltodextrin, and eliminate dextrose since it is so proficient? Ah, once again it is not that simple. Shi. X et al. in an outstanding study, tested the digestive effects of two substrates (any substance acted upon by an enzyme) as opposed to only one substrate in the small intestine. What they found was quite fascinating. The solution containing two substrates stimulated the activation of more transport mechanisms in the intestinal lumen, than did its singular counterpart. Therefore, more carbohydrates were transported out of the small intestine (absorbed into the blood), which additionally aided a greater absorption rate of water into the blood stream (by osmosis). Thus, the higher activation rate of transport mechanisms, even with higher osmolarity facilitated faster energy uptake and hydration (12)!
One of these mechanisms is the glucose/Sodium co transport system (discussed in further detail shortly). When a proper amount of sodium and glucose are combined, an even greater amount of glucose is absorbed, and in turn, a higher rate of H20 is absorbed. Thus, dextrose increases fluid uptake, and contributes to blood glucose maintenance. Which in turn helps spare liver and muscle glycogen from being depleted (4,5,6).
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