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Anyone tried using only dextrose, like in dry form (Dextrotabs) or dissolved powder, on longer rides? Enters the bloodstream in directly usable form, from what I can tell. Seems that if you want energy quickly, involving the fewest chemical processes in the body, this is the way to go. Some have raised the issue of "insulin spike", but I'm not sure that applies while exercising hard, or if the you meter the consumption of dextrose evenly.

I will likely try this anyway, as maltodextrin products seem to wreak havoc on my digestive system, taking too long to enter my bloodstream.

Thoughts?

Plus, it's dirt cheap in powdered form.
 

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I started using dextrose on its own with the juice of a small lemon and a little salt about 3 weeks ago works as good as any sports drink does't upset me in any way, and this has been during V02 and 20-120 minute intervals, I went looking for multodextrin in the supermarket and all I found was dextrose in the home brewers section. Like you said cheap and didn;t give me a sugar crash while doing some moderate exersise.
l mixed 1g per kilo body weight in 500ml water.
 

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Fixed said:
Anyone tried using only dextrose, like in dry form (Dextrotabs) or dissolved powder, on longer rides? Enters the bloodstream in directly usable form, from what I can tell. Seems that if you want energy quickly, involving the fewest chemical processes in the body, this is the way to go. Some have raised the issue of "insulin spike", but I'm not sure that applies while exercising hard, or if the you meter the consumption of dextrose evenly.

I will likely try this anyway, as maltodextrin products seem to wreak havoc on my digestive system, taking too long to enter my bloodstream.

Thoughts?

Plus, it's dirt cheap in powdered form.
Eload is a sports drink with dextrose and a bit of sucrose so that it is palatable. It is a highly regarded for those that are prone to stomach upset. It may be worth checking out.
 

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Sugar is sugar

Fixed said:
I will likely try this anyway, as maltodextrin products seem to wreak havoc on my digestive system, taking too long to enter my bloodstream. Thoughts?
Maltodextrin may bother your gut, though this would be surprising since is it really just polymeric sugar. My guess would be that it is something else in the stuff you're drinking, unless you're mixing up maltodextrin directly. At any rate, maltodextrin has the same glycemic index as glucose, so it is pretty hard to argue that it takes too long to hit your bloodstream.
 

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Discussion Starter · #6 ·
thoughts?

Kerry Irons said:
Maltodextrin may bother your gut, though this would be surprising since is it really just polymeric sugar. My guess would be that it is something else in the stuff you're drinking, unless you're mixing up maltodextrin directly. At any rate, maltodextrin has the same glycemic index as glucose, so it is pretty hard to argue that it takes too long to hit your bloodstream.
Thoughts on this?


Fueling During Exercise
Asker Jeukendrup, PhD, FACSM
Professor of Exercise Metabolism
School of Sport and Exercise Sciences
University of Birmingham
United Kingdom

KEY POINTS

Carbohydrate intake during exercise can delay the onset of fatigue, improve endurance capacity and exercise performance during prolonged (>2h) exercise.
Carbohydrate feeding may also improve exercise performance during exercise of shorter duration and higher intensity (approximately 1 h) although the mechanisms are different.
Small amounts of carbohydrate already have an effect on performance. It is not clear if there is a dose response relationship but emerging evidence suggests that a greater contribution of ingested carbohydrate may result in better performance.
A single carbohydrate can only be oxidized at rates up to 60 grams per hour.
Breakthrough research at the University of Birmingham has shown that when a combination of carbohydrates is used (i.e. glucose and fructose) oxidation rates can increase by 75% up to 105 grams per hour if large amounts of carbohydrate are ingested.
The ingestion of energy dense carbohydrate solutions will slow fluid delivery and can lead to GI discomfort in some individuals. Impairment of fluid delivery is reduced and GI distress less likely when combinations of carbohydrate are ingested.
The amount of carbohydrate to be ingested for performance improvement is best individually determined and a balance should be struck between increasing carbohydrate availability during exercise and minimizing gastrointestinal distress.

Introduction
There is a large body of evidence dating back to the 1920s but mostly from the 1980s that carbohydrates can improve performance during more prolonged exercise (>2h). The ingested carbohydrate can prevent a drop in blood glucose concentration and can help to maintain high rates of carbohydrate oxidation which is necessary to maintain relatively high exercise intensities. We and other have also demonstrated that carbohydrate during exercise can also improve high intensity exercise as short as 1h although the mechanisms may be central rather than metabolic. 1-3 A greater contribution of exogenous carbohydrate (carbohydrate from a drink or food) will spare body carbohydrate stores and is generally believed to be beneficial. Over the last 15 years we have investigated ways to improve fuel delivery to the working muscle.

Oxidation of ingested carbohydrate
Several factors have been suggested to influence exogenous carbohydrate oxidation including feeding schedule, type and amount of carbohydrate ingested and the exercise intensity and these have been intensively investigated. Some of these factors have only small effects other factors major effects on exogenous carbohydrate oxidation. For example, the timing of feeding, the training status of the subjects4, gender5and the exercise intensity have relatively small effects. More important seems to be the type of carbohydrate and the amount ingested. Some types of carbohydrate are oxidized more readily than others6,7. Roughly they can be divided into two categories: carbohydrates that can be oxidized at rates up to 60 g/h (glucose, maltodextrin, sucrose, and maltose) and carbohydrates that can be oxidized at rates up to 30 g/h (fructose, galactose, amylose).

From a large number of studies in the literature it can be concluded that oxidation of orally ingested carbohydrate (from a single source) may already be optimal at ingestion rates around 60-70 g/h and will not exceed 60 g/h. Ingesting more than this will not further increase carbohydrate oxidation rates and is more likely to be associated with gastro-intestinal discomfort. This has therefore been the general guideline: ingest up to 60 g of carbohydrate per hour.




FIGURE 1. Oxidation of multiple transportable carbohydrates This figure is compiled from a large number of studies investigating exogenous carbohydrate during exercise 8-15. The grey bars represent the rate of carbohydrate intake in these studies (expressed in grams per minute). The colored bars represent the peak oxidation rates observed after 90-150 min of exercise. Glucose oxidation in these studies peaked at 0.83 g/min. However if multiple transportable carbohydrates were ingested at high rates (up to 2.4 g/min) very high rates of exogenous carbohydrate oxidation were achieved (up to 1.75 g/min).

Multiple transportable carbohydrates The reason that exogenous carbohydrate oxidation is limited to approximately 60 grams per hour is most likely due to intestinal absorption (for review and detailed discussions see 7). It is suggested that by feeding a single carbohydrate source (for example glucose or maltodextrin) at high rates, the sodium dependent glucose transporters (SGLT1) become saturated. Once these transporters are saturated feeding more of that carbohydrate will not result in greater absorption and increased oxidation rates. By using an additional carbohydrate which uses a different transporter for absorption (i.e., fructose uses the glucose transporter GLUT5), the total amount of carbohydrate absorbed can be increased and fuel supply to the muscle is enhanced.

In one of the first studies we observed an increase in oxidation by 45% of a drink containing glucose:fructose (2:1) compared with a similar amount of glucose! In the following years we tried different combinations of carbohydrates and also different amounts in an attempt to see what the maximal contribution could be of exogenous carbohydrate 8-15. We observed that very high oxidation rates were reached with combinations of glucose+fructose, maltodextrin+fructose and glucose+sucrose+fructose. The highest rates were observed with a mixture of glucose and fructose ingested at a rate of 144 g/h. With this feeding regimen exogenous CHO oxidation peaked at 105 g/h! This is 75% higher than what was previously though to be the absolute maximum! These high intake rates may not always be practical but the findings are convincing enough to tweak the old guidelines. The guideline for carbohydrate intake is therefore: ingest a blend of carbohydrates and increase the intake up to 75-125 g/h.

Performance The increased oxidation of ingested carbohydrate has been suggested to be beneficial for performance but concrete evidence for this has not yet been published. From a laboratory study in which subjects cycled for 5 hours with water, glucose or glucose+fructose there are some indications that drinks with multiple carbohydrates could improve performance 14. In this study carbohydrate was ingested at a rate of 90 g/h. The first indication of improved performance was that subjects’ rating of their perceived exertion tended to be lower with glucose+fructose compared with glucose, which in turn was lower than water placebo. In fact with water not all participants were able to complete the 5 h at 50%VO2max. In addition, the self selected cadence dropped significantly with water, which is generally seen as an indication of developing fatigue. With glucose this was somewhat prevented but with glucose+fructose cadence was highest and remained almost unchanged from the beginning of exercise 14. We have since performed a study to confirm the beneficial effects of glucose+fructose drinks compared with glucose on prolonged exercise performance (Currell et al unpublished findings).

Gastro-intestinal discomfort during exercise Drinks containing carbohydrates that use different transporters for intestinal absorption seem to result in a smaller amount of carbohydrate remaining in the intestine and therefore osmotic shifts and malabsorption may be reduced. This probably means that drinks with multiple transportable carbohydrates are less likely to cause gastro-intestinal distress. Interestingly, this is a consistent finding in studies that have attempted to register gastro-intestinal discomfort during exercise carbohydrate 8-15. Subjects tended to feel less bloated with the glucose+fructose drinks versus glucose drinks. The tolerance of carbohydrate drinks and development of GI distress seems highly individual and therefore strategies for carbohydrate intake will always have to be developed on an individual basis.

Carbohydrate and fluid delivery
Often it is advised to avoid the intake of highly concentrated carbohydrate solutions because these solutions have been shown to delay gastric emptying and fluid absorption. Although there is a lot of evidence to support this there are also observations that impairment of fluid delivery is minimized when combinations of multiple transportable carbohydrate are ingested. Fluid delivery with a glucose+fructose solution has been shown to be greater than fluid delivery from a glucose solution 13.

SUMMARY
In summary, carbohydrate intake during exercise can improve exercise performance especially during prolonged exercise. An increased contribution of the ingested carbohydrate to the energy supply is generally believed to be beneficial. The maximal contribution of a single carbohydrate is approximately 60 grams per hour. Groundbreaking research at the University of Birmingham, however, has shown that when a combination of carbohydrates is used (i.e. glucose and fructose) oxidation rates can increase by 75% up to 105 grams per hour if large amounts of carbohydrate are ingested. These mixtures also seem to help fluid delivery and reduce GI distress compared with a single carbohydrate. The amount of carbohydrate to be ingested for performance improvement is best individually determined and a balance should be struck between increasing carbohydrate availability during exercise and minimizing gastro-intestinal distress.

REFERENCES

Carter, J.M., Jeukendrup, A.E., Mann, C.H. & Jones, D.A. The effect of glucose infusion on glucose kinetics during a 1-h time trial. Med Sci Sports Exerc 36, 1543-1550 (2004).
Carter, J.M., Jeukendrup, A.E. & Jones, D.A. The effect of carbohydrate mouth rinse on 1-h cycle time trial performance. Med Sci Sports Exerc 36, 2107-2111 (2004).
Jeukendrup, A.E., Brouns, F., Wagenmakers, A.J.M. & Saris, W.H.M. Carbohydrate feedings improve 1 h time trial cycling performance. Int J Sports Med 18, 125-129 (1997).
Jeukendrup, A.E., Mensink, M., Saris, W.H.M. & Wagenmakers, A.J.M. Exogenous glucose oxidation during exercise in endurance-trained and untrained subjects. J Appl Physiol 82, 835-840 (1997).
Wallis, G.A., Dawson, R., Achten, J., Webber, J. & Jeukendrup, A.E. Metabolic response to carbohydrate ingestion during exercise in males and females. Am J Physiol Endocrinol Metab 290, E708-715 (2006).
Jeukendrup, A.E. & Jentjens, R. Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research. Sports Med 29, 407-424. (2000).
Jeukendrup, A.E. Carbohydrate intake during exercise and performance. Nutrition 20, 669-677 (2004).
Jentjens, R.L., Venables, M.C. & Jeukendrup, A.E. Oxidation of exogenous glucose, sucrose, and maltose during prolonged cycling exercise. J Appl Physiol 96, 1285-1291 (2004).
Jentjens, R.L., Moseley, L., Waring, R.H., Harding, L.K. & Jeukendrup, A.E. Oxidation of combined ingestion of glucose and fructose during exercise. J Appl Physiol 96, 1277-1284 (2004).
Jentjens, R.L., Achten, J. & Jeukendrup, A.E. High oxidation rates from combined carbohydrates ingested during exercise. Med Sci Sports Exerc 36, 1551-1558 (2004).
Jentjens, R.L. & Jeukendrup, A.E. High rates of exogenous carbohydrate oxidation from a mixture of glucose and fructose ingested during prolonged cycling exercise. Br J Nutr 93, 485-492 (2005).
Jentjens, R.L., et al. Oxidation of combined ingestion of glucose and sucrose during exercise. Metabolism 54, 610-618 (2005).
Jentjens, R.L., et al. Exogenous carbohydrate oxidation rates are elevated after combined ingestion of glucose and fructose during exercise in the heat. J Appl Physiol 100, 807-816 (2006).
Jeukendrup, A.E., et al. Exogenous carbohydrate oxidation during ultraendurance exercise. J Appl Physiol 100,1134-1141 (2006).
Wallis, G.A., Rowlands, D.S., Shaw, C., Jentjens, R.L. & Jeukendrup, A.E. Oxidation of combined ingestion of maltodextrins and fructose during exercise. Med Sci Sports Exerc 37, 426-432 (2005).


http://www.powerbar.com/NutritionRe....aspx?id=2186B868-C2D0-4FB6-8D22-1092DE98480D
 

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Fixed said:
Thoughts on this?
Fueling During Exercise
Asker Jeukendrup, PhD, FACSM
That's the work I've been touting here for a while. I've been making my own maltodextrin/fructose drink (with some electrolytes and flavoring) at those concentrations for several months now and it seems to be working fine. No indigestion or GI issues even with a 24 ounce bottle with somewhere around 400 kcal per hour.
 

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Wow, then according to the above study, maltodextrin would seem to have no place
in the carbohydrate intake component chain, since its inclusion would be to no gain.
This flies in the face of what I had previously been reading, which was that maltodextrin
was more readily assimilated and converted into glycogen stores.
 

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Dwayne Barry said:
That's the work I've been touting here for a while. I've been making my own maltodextrin/fructose drink (with some electrolytes and flavoring) at those concentrations for several months now and it seems to be working fine. No indigestion or GI issues even with a 24 ounce bottle with somewhere around 400 kcal per hour.
What ratio are you using? I do not see the optimal ratio in the study - did I miss it? What is your fructose source? - TF

EDIT: Also wonder if there are additional transport sites for galactose, xylose and ribose. ??? - TF
 

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phoehn9111 said:
Wow, then according to the above study, maltodextrin would seem to have no place
in the carbohydrate intake component chain, since its inclusion would be to no gain.
This flies in the face of what I had previously been reading, which was that maltodextrin
was more readily assimilated and converted into glycogen stores.
The maltodextrin study was done by Hammer - not the best source and, though the advertisement looks very scientific, kind of vague on what it does. There may be a stomach emptying advantage with maltodextrin over glucose and there appears to be no disadvantage. – TF
 

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Discussion Starter · #12 · (Edited)
source

TurboTurtle said:
The maltodextrin study was done by Hammer - not the best source and, though the advertisement looks very scientific, kind of vague on what it does. There may be a stomach emptying advantage with maltodextrin over glucose and there appears to be no disadvantage. – TF
This looks like a great source: http://www.bulkfoods.com/baking.asp?referrer=goodex

Went by and bought some Powerbar Endurance Formula yesterday, thinking from its website that it used the 2:1 dextrose to fructose ratio. Got home, and then noticed that the ingredients list the sugars in order "maltodextrin, fructose, dextrose". Now I have no idea how much of what is in there. I don't get it, their website touts the 2:1 as so fantastic, but then it's product doesn't match it?

I think I'll just make my own. Looks like you can buy less than $20 worth of bulk goods that would be a pretty good value: 5 lbs. of dextrose = $8.16; 5 lbs. of fructose = $10.88 (but using only 2.5 lbs to get the right ratio); about $2 for salt...

5 lbs. of dextrose = 2240 grams x 3.6 kcal / gram = 8064 kcal

2.5 lbs of fructose = 1120 grams x 3.6 kcal / gram = 4032 kcal

total 12096 kcal

240 kcal / hr = 50 hours

50 hours at 15 mph ave = 750 miles

$20 for 750 miles is dirt cheap (assume the water is free)

ADDED:

Looked up Sustained Energy prices for comparison:

A 30 serving container is $53. Each serving is 85 grams, so that works out to 30x85=2550 grams, or 5.7 lbs; $9.29 / lb. (but it does contain other ingredients)

My example above of dextrose/fructose/salt, at $20 for 7.5 lbs = $2.60 / lb.

At the same website, plain maltodextrin is $8.53 for 5 lbs., or $1.71 / lb.
 

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Actually, the maltodextrin dogma is espoused by Cytomax. I am not ready to
dismiss that rationale in favor of the new study. I am sure there have been a few
studies and we are seeing just one here. Cytomax works for me, very well, in
fact much better than gatorade, no comparison. I will not be throwing my 4.5lb
can away any time soon. And it's so much easier than having to formulate and mix
my own homebrew, not to mention the fact that it contains 5 electolytes, as opposed
to just sodium and potassium and that aspect of hydration is perhaps even more
important than carbohydrate maintenance.
 

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Discussion Starter · #15 ·
how long?

Dwayne Barry said:
That's the work I've been touting here for a while. I've been making my own maltodextrin/fructose drink (with some electrolytes and flavoring) at those concentrations for several months now and it seems to be working fine. No indigestion or GI issues even with a 24 ounce bottle with somewhere around 400 kcal per hour.
I have found that I can handle anything for up to about 4 hours, but the longer I go, peaking around 10 hours, unabsorbed carbs in the lower intestine cause big time problems. So, for me, the test does not really even begin until about 4-5 hours of continuous hard riding.
 

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TurboTurtle said:
The report above just says that 2:1 was the first study and that they tried other ratios but never says what the results were. - TF
You could probably go a little richer on the fructose. Glucose topping out at about 60g/hour seems pretty well established and they used an additiional 30g/hour fructose in the studies that showed performance benefits for the 2/1 ratio with a 1.5g per min of carbs. But studies have shown up to about a 1.75g/min oxidation rate of the exogenous carbs as the max. So maybe an extra .25g/min of fructose could be used, or 45g/hour rather than 30g/hour.

The mix I use is probably a little rich since I put in just under a cup of malto which I think is about 300kcal, and I figured about 1/5th a cup was about 30g of the fructose I have, but I just use a 1/4 cup so I might be getting close to about 40g of fructose. I would say I'm probably closer to ~450kcal rather than 360kcal of a 1.5g/min mix and it still works fine for me.
 

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Argues for food

Fixed said:
Thoughts on this?


Fueling During Exercise
Asker Jeukendrup, PhD, FACSM
Professor of Exercise Metabolism
School of Sport and Exercise Sciences
University of Birmingham
United Kingdom

KEY POINTS

Carbohydrate intake during exercise can delay the onset of fatigue, improve endurance capacity and exercise performance during prolonged (>2h) exercise.
Carbohydrate feeding may also improve exercise performance during exercise of shorter duration and higher intensity (approximately 1 h) although the mechanisms are different.
Small amounts of carbohydrate already have an effect on performance. It is not clear if there is a dose response relationship but emerging evidence suggests that a greater contribution of ingested carbohydrate may result in better performance.
A single carbohydrate can only be oxidized at rates up to 60 grams per hour.
Breakthrough research at the University of Birmingham has shown that when a combination of carbohydrates is used (i.e. glucose and fructose) oxidation rates can increase by 75% up to 105 grams per hour if large amounts of carbohydrate are ingested.
The ingestion of energy dense carbohydrate solutions will slow fluid delivery and can lead to GI discomfort in some individuals. Impairment of fluid delivery is reduced and GI distress less likely when combinations of carbohydrate are ingested.
The amount of carbohydrate to be ingested for performance improvement is best individually determined and a balance should be struck between increasing carbohydrate availability during exercise and minimizing gastrointestinal distress.
IMO, this is a simple argument for real food, which by its very nature, contains a mixture of carbohydrates. There's nothing fundamentally wrong with developing carb mixtures, but they are really just trying to approach the benefits of food. Things like dried fruits, peanut butter on bread, salty ham and cream cheese on a bun, etc. are pretty good sources and have been (and continue to be) used by professional riders in long races.
 

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Kerry Irons said:
IMO, this is a simple argument for real food, which by its very nature, contains a mixture of carbohydrates. There's nothing fundamentally wrong with developing carb mixtures, but they are really just trying to approach the benefits of food. Things like dried fruits, peanut butter on bread, salty ham and cream cheese on a bun, etc. are pretty good sources and have been (and continue to be) used by professional riders in long races.
Makes sense but you would think when you start adding fat, fiber and/or significant amounts of protein, gastric emptying might slow and becoming the limiting factor in exogenous carbohydrate use rather than carbohydrate transport across the intestinal walls, which was essentially the old paradigm. I've not seen any study that looked at that, probably would be hard (impossible?) to mark the carbohydrates so you could measure exogenous carbohydrate use, but I suppose you could always measure performance.
 

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Fast and slow

Dwayne Barry said:
Makes sense but you would think when you start adding fat, fiber and/or significant amounts of protein, gastric emptying might slow and becoming the limiting factor in exogenous carbohydrate use rather than carbohydrate transport across the intestinal walls, which was essentially the old paradigm. I've not seen any study that looked at that, probably would be hard (impossible?) to mark the carbohydrates so you could measure exogenous carbohydrate use, but I suppose you could always measure performance.
The ham & cheese sandwich is still a staple in the professional peloton during long races. I typically consume a big handful of salted mixed nuts during a long ride. However, for shorter distances, you can obviously go with a "pure carb" source of food, like dried fruit, fig bars, etc. It is all about thinking it through and then trying different things to see what works for you. I used to ride with a guy whose mid-ride snack was chocolate milk and cottage cheese (not the low-fat version of either). He never seemed to have any problems from it, though just the thought of it made it impossible for me to watch him eat it :)
 

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Discussion Starter · #20 ·
worth a try

Kerry Irons said:
IMO, this is a simple argument for real food, which by its very nature, contains a mixture of carbohydrates. There's nothing fundamentally wrong with developing carb mixtures, but they are really just trying to approach the benefits of food. Things like dried fruits, peanut butter on bread, salty ham and cream cheese on a bun, etc. are pretty good sources and have been (and continue to be) used by professional riders in long races.
The real food alternative might be worth a try, as nothing else is working. Tried the Powerbar Endurance yesterday, and still got stomach upset around 4 hours (riding very hard up mountains, though). Have some bulk dextrose and fructose on order.

One thing I wonder is whether the bread and cracker type foods might help avoid stomach upset.

I'm so disgusted with my stomach being my primary limiting factor on long rides that I'll try just about anything. It's frustrating to be able to ride 100 miles in 4 1/2 hours, but feel like I'm going to puke the whole time as a result.
 
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