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Sucrose,glucose and fructose 101?

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My technical knowledge of these different chemical makeups of "sugar" is confusing to me. Can someone in layman terms define and differetiate what the significance to energy in humans each consists. Which provides energy and which takes more energy to breakdown. How does it realte to food groups and what is essentially good and bad? For climbers (an other athletes) what is the best way to think of these sugars in terms of consmuption in times of active and post active movement.

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Sucrose is the primary product of photosynthesis. Plants then metabolize this into fructose and glucose. In your body, the sucrose (table sugar), a disaccharide must be broken into monosaccharides such as glucose and fructose before it can be used, hence it takes longer to get the energy from it. Sucrose is broken down in the intestine to its components, glucose and fructose. These two sugars are absorbed into the bloodstream and carried directly to the liver. Some fructose is converted into glucose in the liver before it is returned to the blood for use as energy. If the glucose is not needed right away to meet energy needs, it is converted to glycogen, the starch-like compound that is the energy reserve of human metabolism. Glycogen can be converted back to glucose when the body needs energy.

I know this didn't answer all of your questions, but maybe it's a start.

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Alright, here's the blurb from the other list:

***There are many more types of sugars than those three but they are the most common. Glucose is the type of sugar that we use in metabolism - before any other type of sugar can be used, it must be converted to glucose. Consuming pure glucose will increase your blood sugar very rapidly (it has a high glycemic index). Fructose is similar in structure to glucose, but must be converted to glucose in the liver before it can be used, this is why it does not increase blood sugar very quickly, and therefore has a surprisingly low glycemic index. Sucrose is a disaccharide, which means it is two sugars attached together, and these two sugars happen to be glucose and fructose. So before sucrose can be absorbed in the small intestine, the enzyme "sucrase" cuts it in half and you then get a glucose and fructose. Not surprisingly, sucrose has a glycemic index right in between glucose and fructose.

Starch, which is usually our main source of carbohydrate as humans, is composed of very long chains glucose. Pure starch can be digested very easily, and although is considered to be a "complex carbohydrate", it alone, or in very refined products such a white bread, has a very high glycemic index.

They all provide energy, and the energy required to get glucose from fructose and sucrose is very small, so they can be considered equal in energy based on the amount (weight) consumed. This comes out to 4.1 Calories per gram.

By the way, big-C "Calories" actually means "kilocalories", which is a thousand little-c "calories". So an apple, for example, has around 100 Calories = 100 kilocalories = 100,000 calories.

They continue:<does it realte to food groups and what is essentially good and bad?For climbers (an other athletes) what is the best way to think ofthese sugars in terms of consmuption in times of active and postactive movement.>

*** During exercise and post-exercise, it is best to consume foods with a high glycemic index that are easily digestible, such as sports drinks or those Goo packets. Around exercise, because our body is actively using up sugars to fuel muscle contraction, the rapid increase in blood glucose is not a problem, it is in fact helpful.

Personally, I don't consume anyting but water unless my workout is longer than 2 hours. Glycogen depletion is probably not a problem in that period of time. But, carbohydrates post-exercise is definitely a good idea, because we are able to pack carbohydrates into the muscles more quickly at that time. Sports drinks and goo are fine for this, but a bagel with jam, a banana, or fruit juice are all acceptable, because they digest fairly quickly and have fairly high glycemic indices. Most people I know prefer to eat "real food" over supplements. Also, real foods have more vitamins and minerals which are useful too.

If you are having a long outdoor climbing day, you don't need to worry about it as much, just snack on things that are high in carbs, low in fat, low-moderate in protein, and have low or moderate glycemic indices.

Lastly, none of them are "good" or "bad". Some are more appropriate sometimes, and others are more appropriate at other times. If you eat enough of any one of them you'll get sick!

Hope this helps,Andrew Pacey

-----Really, really friggin long, and probably way, way more info than you wanted, but hopefully it's clear enough . . .

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If you really want an earful on energy utilization for endurance athletes, go tothe phil maffetone web page. This guy has a very unorthodox approach, but I happen to believe he's on the right track. He's down on the heavy carbs and more into balancing it out with protein. For me, this approach has been essential in keeping me from bonking, not only on a climb but even in a normal day at work.

It may not be true for every person's metabolism, but for some of us the tendency to rely too heavily on carbohydrates leads to a chronically high insulin state, which means if we don't constantly fuel ourselves with carbos then sooner or later our blood sugar will plunge, with unpleasant results. I have found that if I add a protein source to my meals or snacks, this keeps me from getting hypoglycemic and ravenous in a few hours. I can keep going on what seems like fewer calories, and avoid the crash. cool.gif" border="0

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David, there is a really good book called The Triathletes Training Bible by Joe Friel that I would recommend for anyone interested in the science of endurance training.


Although the book is about training for triathlons most of what is said really applies to endurance sports in general and I find it really resourceful.

The nutrition part doesn't go into extreme details but is a good general survey of nutrition etc. and gives references to more comprehensive material. One of the big things I took out of it is training your body to use your fats stores instead of ingested sugars and glycogen. This is accomplished by watching the sugars and carbs that you eat. A professional triathlete can go 3 hours on the stored glycogen but like 40 hours on fat stores. I found the section on eating for the Ironman interesting because it went over what your body lost in nutrients and water and what would need to eat every hour to make up for that. Obviously the Ironman is on a much different scale than alpine climbing but the principle of going nonstop for extended time over 10 hours is the same.

Anyways for anyone not well versed in metabolism and sports nutrition I think this is an excellent intro, and the book is cheap.

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the maltodextrin story I got was that because it is a polysaccharide the extra step of chopping off the glucoses means absorption and rate of increase of blood sugar is slower than if you consume just glucose or fructose straight-up. This translates to a longer time before bonking, so if you can get a goo shot every 45min or so your blood sugar should be more even than if you are knocking back raspberry jam instead.

my 'source' also figures that those secret magic ingredient trace minerals and junk that the xtreem-baby-food companies tout as the key to the performance of their snake oils are actually just by-products of the corn-starch-to-maltodextrin synthesis process. So if you make your own out of maltodextrin from the homebrew shop you will be picking up some of those mini ingredients anyways.

perhaps this is all BS though, I am no xtreem x-spurt. tongue.gif" border="0

I have also heard from a few athletic type people (martial arts) that consuming refined sugar causes them joint pain confused.gif" border="0

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Originally posted by David Parker:

My technical knowledge of these different chemical makeups of "sugar" is confusing to me. Can someone in layman terms define and differetiate what the significance to energy in humans each consists. Which provides energy and which takes more energy to breakdown. How does it realte to food groups and what is essentially good and bad? For climbers (an other athletes) what is the best way to think of these sugars in terms of consmuption in times of active and post active movement.

The glycemic index (GI) of the sugars is more of a concern than the energy content of the individual sugars. Glucose, sucrose, and fructose are absorbed into the blood stream at different rates. If glucose is used as the standard at 100, sucrose is about 65 and pure fructose is 22 (high fructose corn syrup is a mix of sugars --about half fructose-- and has a GI of 50). Maltodextrin, which is a di-glucose, has a GI of 105. It's used in a lot of "energy" products because it's cheap and provides such a quick boost in blood sugar. The bummer with eating high GI foods is that blood sugar levels will spike, then drop below basal levels pretty fast (around 20 minutes for most people) causing the user to feel crummy. Combining the sugars with other nutrients will moderate this. (eg. Proteins are utilized as energy about 3 to 4 hours after eating, so combining sugars with protein will help avoid spiking and crashing. Fats slow absorption. I won't even get into motility issues). The amino acids (valine and leucine, usually) and salts put into some energy food products have been shown to improve athletic performance over sugars alone.

So, if you want a quick energy boost, eat a high GI food. But if you want that energy to last, temper it with some mid and low GI foods. One study at Ohio State showed that a Snickers bar is pretty good in this respect, whereas a Power Bar caused a quick spike and drop in blood sugar. The take-home message is to eat whole foods that naturally have a combination of nutrients. Climbers are generally operating at a low aerobic level where we're burning fats along with sugars, so eat some fat (seed and fish oils are quite good for you; essential, even). Eat tasty stuff that's good for you that you'll like. Food won't do anything if you can't stomach it.

hope this helps.

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Maltodextrin comes from corn starch, and is basically maltose with a bunch of other crap. Maltose is a disaccharide like sugrose but has two glucose groups instead of one glucose and one fructose, so it has a higher glycemic index.

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