maltodextrin is a polysaccharide made from hydrolyzed starch. hydrolyzing longer chain starches produces shorter chain carbohydrates similar to sugar, but still somewhat different. enzymes are used to break the starches down into shorter chain carbohydrates. often potato or corn starches are used as the source starches to be hydrolyzed.
maltodextrins are easily absorbed into the blood. as such, they are used for quick energy. when combined with more simple sugars, more transport mechanisms are activated in the lumen of the gut than if simple sugars alone are ingested. this increases the rate of total carbohydrate absorption.
obviously, adequate quantities of water should be consumed simulataneously to permit absorption of these nutrients, as well as to replace water lost through physical activity. failure to consume adequate quantities of water while consuming large amounts of carbs can actually cause water to leave the blood stream and enter the intestines. remember osmosis? it will work backwards to what an athelete/hiker desires, if adequate water is not consumed. ever read carefully the instructions with Gu or Energy bars? IIRC, they all recommend drinking a reasonable quantity of water with the product.
i'm not sure that i completely agree with Mfr's statements that maltodextrin's supply long burning energy (IIRC depends in part on what else is ingested with it). they really are, in one sense, closer to sugars than to non-hydrolyzed starches. best i can recall, digestion is somewhat similar for all carbohydrates however (i.e. most of it occurs in the small intestines and not the stomach due to the higher pH and presence of enzymes), but absorption rates, when individual carbs are consumed alone, differ depending upon a number of factors. however, such energy sources (viz. maltodextrin and sugars) are either useful or necessary when high levels of muscular exertion is engaged in for extended periods of time. under certain high intensity exercise conditions, one downside of maltodextrin when consumed alone is the increase of utilization of muscle glycogen stores vs. consuming maltodextrin plus a simple sugar source.
[note: the following post references a document which disputes one of the above statements regarding maltodextrin, if interested, please be sure to read it.]
however, having stated all this, when hiking 10-14 hrs per day over rough terrain with many elevation changes, i periodically consume Clif bars and sometimes Gu for the energy they provide. both products sure are convenient.
sorry, that's 'bout all i can recall about maltodextrins that's pertinent. best to check with a good Biochem textbook or Sports Physiology textbook for more accurate/detailed/current info.
on a somewhat related note which might be of interest to some (if not, don't bother to read):
depending upon the level of physical exertion and your body's related heart rate, your muscles will burn "fuels" in different ratios - subject to the availability of oxygen being transported into muscle cells. More specifically the hiker is engaged in a long duration moderate intensity form of exercise. So, a "ballpark"/approximate breakdown of the "fuels" utilized is normally as follows:
25% each from:
-- fat stored as triglycerides within the muscle
-- carbohydrate stored as the starch glycogen within the muscle
-- glucose released into the bloodstream from the liver.
-- fat coming from diet or released from storage in adipose tissue
if at all possible, our bodies don't like to exclusively use just energy sources stored in the muscles, thereby depleting/exhausting them completely, just in case some sort of "surpreme" exertion is attempted/required. our bodies don't want to let us down if at all possible. how's that for an intelligent design!
as exercise intensity increases beyond a certain level, approx. the same amount of fat is "burned" (the absolute amount depends upon "cardio" conditioning which is related to the amount of oxygen available in the red corpuscles in the blood), and any increased energy demand is met by burning more carbohydrate, so the ratio of carbohydrate to fat increases.
a typical value one often reads, for a long distance hiker, for depletion of stored glycogen reserves, is approx. 6hrs. i've never been able to determine a continuous heart rate associated with this 6hr figure. my guess might be ~60% of the so-called age-adjusted-maximal-heart-rate, but this is just a guess. frequent "snacking" while hiking is a good strategy for preventing depletion and replenishing these energy stores.