Post-workout is the one time that high-glycemic carbs are preferred. This term refers to carbs that are high on the glycemic index. This is a measure of how quickly a food raises blood sugar and hence insulin levels. Normally, it is best to eat lower glycemic foods so as not to initiate an insulin spike. But post-workout, the exact opposite is true. The elevated insulin levels will help to drive nutrients into the muscle cells.

Moreover, speed is of the essence. It is vital to get the carbs to the muscle cells as quickly as possible. And again, high-glycemic carbs are preferred to lower glycemic carbs for this purpose.

Usually, when one thinks of high-glycemic carbs one thinks of simple sugars. However, most simple sugars would not be beneficial to consume post-workout. Non-beneficial sugars would include fructose, sucrose, and lactose.

As for the first, fructose ("fruit sugar") is very low-glycemic as compared to other sugars. So it is not digested quickly and does not significantly raise insulin levels. Moreover, fructose cannot be used by the body to restore muscle glycogen. What this means is that fruit juice is not a good source of carbs for the post-workout drink.

As for sucrose ("table sugar"), it is a disaccharide consisting of one molecule of fructose and one of glucose. So sucrose is half fructose. And again, fructose cannot be used to restore muscle glycogen. And half of your carbs from fructose would not be beneficial.

So foods high in sugar (sucrose) content or high in high fructose corn syrup content like soda would not be beneficial post-workout. So the need for high glycemic carbs post-workout does not give the exerciser an excuse to consume junk food post-workout. You won't be doing your body any good, nor will you be giving it what it needs.

As for lactose ("milk sugar"), its glycemic rating is moderate, higher than fructose but lower than sucrose. It is also a disaccharide constituting of one molecule of galactose and one of glucose. So it is half galactose. And again, galactose can be used by the body to restore liver glycogen but not muscle glycogen. So again, in small amounts it might be okay, but it should not be the primary carb. What this means is that milk would not be a good source of carbs post-workout.

So what would be good sources? Complex carbs like those found in breads and cereals can be used to restore muscle glycogen. And at other times, complex carbs are the best source of carbs. However, post-workout, healthy carb containing foods like whole grain breads and cereals would not be good.

The fiber in such foods would delay digestion. For this reason, the glycemic rating of unrefined complex carb foods is usually low to moderate. And even refined breads and cereals, with their moderate glycemic rating, would take too long to digest. And again, a liquid post-workout drink would be better than solid foods.

So what that leaves as the main options are dextrose and maltodextrin. Dextrose is simply the name for glucose that has been derived from corn. Glucose is the body's primary energy source, and the form in which carbs must be converted into to be used to create glycogen.

Moreover, dextrose can be absorbed directly through the gut into the bloodstream. And with this rapid absorption, it raises blood sugar and insulin levels faster than any other carb. And since it is already in the form the body requires, it can be used immediately for glycogen replenishment.

Maltodextrin, on the other hand, is actually a complex carb. But its molecular chain is shorter than other complex carbs. Moreover, it is consists of loosely bonded glucose molecules. And like dextrose, maltodextrin is absorbed directly through the gut. So it raises blood sugar and insulin levels as much as dextrose does.

However, before maltodextrin can be utilized, it must first pass through the liver for the bonds between the glucose molecules to be broken down. So the rate at which it is used for glycogen replenishment is slower than with dextrose. However, because it is metabolized slower, there will not be as quick of a drop of insulin and blood sugar levels as with dextrose.

מקור:
http://www.fitnessforoneandall.com/powerlifting/article/diet/post-workout/part_one.htm

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