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  1. #1
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    High Glycemic Index Foods as Energy Fuel?

    This is something that has been bothering me for a while. The Gatoride vs. Cytomax click here thread got me thinking about it. I don't know the answer.

    Here's my question:

    If you put any high glycemic food/sugar into your blood while exercising, i.e. Gatorade, Bananas, Clif Bars, etc., shouldn't you have a corresponding low blood sugar episode shortly thereafter? Correct me if I'm wrong, but doesn't a sudden spike in blood sugar also cause a spike in insulin, AKA hypoglycemia? Wouldn't this cause a "bonking" effect?

    It would seem to me that high sugar foods would be counter-productive to endurance activities like biking where you spend a long time in the saddle. Am I missing something?

  2. #2
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    Sure. You're missing the point that this is something created for diabetics, not folks involved in sports.

    Koffee

  3. #3
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    Quote Originally Posted by Paul W.
    If you put any high glycemic food/sugar into your blood while exercising, i.e. Gatorade, Bananas, Clif Bars, etc., shouldn't you have a corresponding low blood sugar episode shortly thereafter? Correct me if I'm wrong, but doesn't a sudden spike in blood sugar also cause a spike in insulin, AKA hypoglycemia? Wouldn't this cause a "bonking" effect?

    It would seem to me that high sugar foods would be counter-productive to endurance activities like biking where you spend a long time in the saddle. Am I missing something?
    These two studies confirm that the glycemic index is not just for diabetics only, it's important for athletes as well:

    ===

    Carbohydrate feeding before exercise: effect of glycemic index.

    Thomas DE, Brotherhood JR, Brand JC.
    Department of Biochemistry, University of Sydney.

    Low glycemic index (GI) foods may confer an advantage when eaten before prolonged strenuous exercise by providing a slow-release source of glucose to the blood without an accompanying insulin surge. To test this hypothesis, eight trained cyclists pedalled to exhaustion one hour after ingestion of equal carbohydrate portions of four test meals: lentils, a low GI food (LGI); potato, a high GI food (HGI), and glucose and water. Plasma glucose and insulin levels were lower after LGI than after HGI from 30 to 60 min after ingestion (p less than 0.05). Plasma free fatty acid (FFA) levels were highest after water (p less than 0.05) followed by LGI and then glucose and HGI. From 45 to 60 min after ingestion, plasma lactate was higher in the HGI trial than in the LGI trial (p less than 0.05) and remained higher throughout the period of exercise. The rank order from lowest to highest for total carbohydrate oxidation during exercise was water, lentils, glucose and potato. Endurance time was 20 min longer after LGI than after HGI (p less than 0.05). These findings suggest that a low GI pre-game meal may prolong endurance during strenuous exercise by inducing less post-prandial hyperglycemia and hyperinsulinemia, lower levels of plasma lactate before and during exercise, and by maintaining plasma glucose and FFA at higher levels during critical periods of exercise.

    ===

    Muscle glycogen storage after prolonged exercise: effect of the glycemic index of carbohydrate feedings

    L. M. Burke, G. R. Collier and M. Hargreaves
    Department of Sports Medicine, Australian Institute of Sport, Australian Capital Territory.

    The effect of the glycemic index (GI) of postexercise carbohydrate intake on muscle glycogen storage was investigated. Five well-trained cyclists undertook an exercise trial to deplete muscle glycogen (2 h at 75% of maximal O2 uptake followed by four 30-s sprints) on two occasions, 1 wk apart. For 24 h after each trial, subjects rested and consumed a diet composed exclusively of high-carbohydrate foods, with one trial providing foods with a high GI (HI GI) and the other providing foods with a low GI (LO GI). Total carbohydrate intake over the 24 h was 10 g/kg of body mass, evenly distributed between meals eaten 0, 4, 8, and 21 h postexercise. Blood samples were drawn before exercise, immediately after exercise, immediately before each meal, and 30, 60, and 90 min post-prandially. Muscle biopsies were taken from the vastus lateralis immediately after exercise and after 24 h. When the effects of the immediate postexercise meal were excluded, the totals of the incremental glucose and insulin areas after each meal were greater (P < or = 0.05) for the HI GI meals than for the LO GI meals. The increase in muscle glycogen content after 24 h of recovery was greater (P = 0.02) with the HI GI diet (106 +/- 11.7 mmol/kg wet wt) than with the LO GI diet (71.5 +/- 6.5 mmol/kg). The results suggest that the most rapid increase in muscle glycogen content during the first 24 h of recovery is achieved by consuming foods with a high GI.

    ===

    Bottom line: eat low-GI prior to a ride, eat or drink high-GI right after a ride.

  4. #4
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    It's important for diabetics and repackaged for athletes. Whatever. It's just yet another modified gimmick diet that seems to work decently for athletes, but at the end of the day, it's a diet for diabetics. It's well known that people who aren't diabetics don't have a clear idea of how to use the glycemic scale: ie- you can eat turkey, which is high glycemic, but you can't eat white bread, which is low glycemic. However, if you eat a turkey sandwich with white bread, that sandwich is a high glycemic food. But for the person who doesn't know any better, they'll look at the glycemic index and x-nay on the bread, when actually, bread isn't such a bad thing. Again, this is a "for example".

    If you're planning on using the glycemic index, get REAL educated on how to properly use it before you start assuming what foods are "good" and "bad".

    Koffee

  5. #5
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    Quote Originally Posted by JamesV
    Bottom line: eat low-GI prior to a ride, eat or drink high-GI right after a ride.
    Interesting post, JamesV.

    After years on the bike, I've determined that for me at least, the pre-ride fuel of choice before a long ride is plain-old oatmeal, a low-GI food. Not only can I tolerate it well (don't feel pukey on the bike), I generally feel strong going into the third hour, just when my friends' energy begins to flag. Carmichael and others all talk about high-GI near the end of the ride and during the post-exercise 'glygogen window.'

    I don't claim any expertise here, but will add that a riding buddy who is diabetic (rides with a tiny electronic insulin pump/monitor thing in his jersey pocket) and very fit (multiple marathons, centuries, etc.) says he can eat powerbars while riding and have his blood sugar stay where he wants it to because the muscles are constantly drawing glucose from the blood. He does have to take some care and manage things when eating after the ride tho.
    Last edited by cg33; 03-24-05 at 04:11 PM.
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  6. #6
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    Quote Originally Posted by koffee brown
    It's important for diabetics and repackaged for athletes. Whatever. It's just yet another modified gimmick diet that seems to work decently for athletes, but at the end of the day, it's a diet for diabetics. It's well known that people who aren't diabetics don't have a clear idea of how to use the glycemic scale: ie- you can eat turkey, which is high glycemic, but you can't eat white bread, which is low glycemic. However, if you eat a turkey sandwich with white bread, that sandwich is a high glycemic food. But for the person who doesn't know any better, they'll look at the glycemic index and x-nay on the bread, when actually, bread isn't such a bad thing. Again, this is a "for example".

    If you're planning on using the glycemic index, get REAL educated on how to properly use it before you start assuming what foods are "good" and "bad".

    Koffee
    Huh?

    Turkey has no carbohydrates, so it has no glycemic index at all!
    White bread (almost all types of bread) has a high glycemic index, not low.
    A turkey sandwich, however, will have a lower GI than the bread alone, as protein slows down the process, resulting in a lower and slower insulin response, which has the same effect as a lower actual GI.

    GI is an excellent way, properly used, to stay healthy. It's not the fad diet so many make it out to be.
    The problem is that it's partly become confused with the somewhat bizarre Atkins diet.

    It's been proven that the actual and only effect of the Atkins diet is that people generally can't eat as much energy when carbs are not allowed (or cut down to a minimum). All the ketosis stuff is nonsense, and has nothing to do with the real reason people successfully lose weight on the Atkins diet.
    It also appears to be a safe and effective method for short-term use (up to 4-6 weeks) but should not be made into a lifestyle. Good as a jumpstart for obese people, though!

  7. #7
    Gitchur SUV Away From Me
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    Quote Originally Posted by cg33
    After years on the bike, I've determined that for me at least, the pre-ride fuel of choice before a long ride is plain-old oatmeal, a low-GI food.
    Woo hoo... a fellow devotee of oatmeal! I love the stuff. Got my wife and daughter turned into oatmeal fans too. Once in a while we'll even say, hey, let's have oatmeal for dinner! Are we nuts or what?
    .
    Quote Originally Posted by Koffee Brown
    It's just yet another modified gimmick diet that seems to work decently for athletes, but at the end of the day, it's a diet for diabetics.
    What CdCf said, I'm referring to the glycemic index of optimal food and drink for the cyclist, not the fad diet.

    Here's an idea for you. Let's go on a 4-hour ride. After three hours, we'll each get one snack. I'll eat French Bread (GI=100+) while you have peanuts (GI under 40). After the last hour of riding I think you'll have a new appreciation of the glycemic index

    I do agree with you about reading and studying up on glycemic index, metabolic pathways, gastric emptying, etc. Human exercise metabolism is complicated (to a non-expert like me, anyway) and there's a tremendous amount of misinformation out there.

  8. #8
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    Quote Originally Posted by CdCf
    Huh?

    Turkey has no carbohydrates, so it has no glycemic index at all!
    White bread (almost all types of bread) has a high glycemic index, not low.
    A turkey sandwich, however, will have a lower GI than the bread alone, as protein slows down the process, resulting in a lower and slower insulin response, which has the same effect as a lower actual GI.

    GI is an excellent way, properly used, to stay healthy. It's not the fad diet so many make it out to be.
    The problem is that it's partly become confused with the somewhat bizarre Atkins diet.

    It's been proven that the actual and only effect of the Atkins diet is that people generally can't eat as much energy when carbs are not allowed (or cut down to a minimum). All the ketosis stuff is nonsense, and has nothing to do with the real reason people successfully lose weight on the Atkins diet.
    It also appears to be a safe and effective method for short-term use (up to 4-6 weeks) but should not be made into a lifestyle. Good as a jumpstart for obese people, though!

    Whoops, switch that. Turkey= low glycemic, and white bread= high glycemic. Wasn't thinking.

    Koffee

  9. #9
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    Quote Originally Posted by JamesV
    Woo hoo... a fellow devotee of oatmeal! I love the stuff. Got my wife and daughter turned into oatmeal fans too. Once in a while we'll even say, hey, let's have oatmeal for dinner! Are we nuts or what?
    .


    What CdCf said, I'm referring to the glycemic index of optimal food and drink for the cyclist, not the fad diet.

    Here's an idea for you. Let's go on a 4-hour ride. After three hours, we'll each get one snack. I'll eat French Bread (GI=100+) while you have peanuts (GI under 40). After the last hour of riding I think you'll have a new appreciation of the glycemic index

    I do agree with you about reading and studying up on glycemic index, metabolic pathways, gastric emptying, etc. Human exercise metabolism is complicated (to a non-expert like me, anyway) and there's a tremendous amount of misinformation out there.
    I would eat what I usually eat for a 4 hour ride and I wouldn't bother with the GI at all. I'd have a fiber based granola cereal about 15 minutes before leaving and either some orange juice (not from concentrate) or gatorade, then during the ride, I'd keep myself refreshed with water and gatorade. If I started feeling like I needed more, I'd have a Pria bar or a Powerbar about halfway through, and then afterwards, I'd have some kind of higher carb meal, and I'd throw in a few pieces of fruit along the way. It's worked for me so far, and my rides average in length from 2 hours to 12 hours.

    I'm not saying it doesn't work, I'm just saying that if you're going to use it, better to educate yourself about the GI, since it's a diet for DIABETICS, not regular folks. Somewhere along the way, desperate athletes found out about the GI scale and figured it would work for them. They got lucky. It can work, but I think a better way to figure it out is to seek a dietitian and have them draw up a good, solid eating plan that's individual to you and your energy needs. I don't believe in fads, gimmicks, or whatever the new schtick is out there. I believe in practicality and dealing with people who can evaluate me as an individual and make recommendations for me.

    Koffee

  10. #10
    Long Distance Cyclist Machka's Avatar
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    Quote Originally Posted by Paul W.
    This is something that has been bothering me for a while. The Gatoride vs. Cytomax click here thread got me thinking about it. I don't know the answer.

    Here's my question:

    If you put any high glycemic food/sugar into your blood while exercising, i.e. Gatorade, Bananas, Clif Bars, etc., shouldn't you have a corresponding low blood sugar episode shortly thereafter? Correct me if I'm wrong, but doesn't a sudden spike in blood sugar also cause a spike in insulin, AKA hypoglycemia? Wouldn't this cause a "bonking" effect?
    It would seem to me that high sugar foods would be counter-productive to endurance activities like biking where you spend a long time in the saddle. Am I missing something?

    Yes, you are correct. High glycemic/sugar foods are a bad choice for anyone, but especially for people doing long distance cycling. They cause a spike in blood sugar which in turn triggers the insulin, which in turn causes a crash in blood sugar. That's why when you eat chocolate in the middle of the afternoon at work, 45 minutes later you feel like taking a nap.

    Spiking the blood sugar like that is only a good idea for a short term extra boost in a situation like a short race, or when you are already on the verge of bonking and need to get your blood sugar up quickly. In the second situation, you should consume the high glycemic/sugar food, and then IMMEDIATELY follow it up with something low glycemic. The low glycemic food will stabilize the blood sugar once it gets up a bit.

    For long distance cycling, one of your best bets for food is something high in fat. Fat is a slow burning fuel and won't cause the spiking and crashes that sugar does. It is also much higher in calories so it will provide you with energy for a lot longer period of time than sugar does.

    I hope this helps clear things up.

  11. #11
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    Okay, so I'm 2 hrs into a tough 3 hr training ride. I've been drinking gatorade but really starting to run out of energy, especially on the hills. Would it be best to eat a powerbar at this point, or consume a gel pack, or both, or neither?

  12. #12
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    Eat your gel pack. At that point, you need quick energy, and powerbars are a slow releasing energy with complex carbs. But then after that, I would eat the powerbar anyway so you can have some energy later on for the last tough part of the ride. By the time that powerbar starts to digest, you'll be towards the end of the ride and you'll have the energy to finish stronger.

    Koffee

  13. #13
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    Quote Originally Posted by cg33
    After years on the bike, I've determined that for me at least, the pre-ride fuel of choice before a long ride is plain-old oatmeal, a low-GI food. Not only can I tolerate it well (don't feel pukey on the bike), I generally feel strong going into the third hour, just when my friends' energy begins to flag.
    Oatmeal's fine, unless you're in a long (multi-hour) race. Then there's the distinct possibility of needing an unscheduled bathroom break at the worst of times. I learned that lesson the hard way. The morning before a race, I stick with liquid nutrition only. Ideal time is 3 hours before the start, but 2 hours before seems to work okay for me.
    Managing Director, Undiscovered Country Tours

  14. #14
    Senior Member Bontrager's Avatar
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    Quote Originally Posted by Paul W.
    This is something that has been bothering me for a while. The Gatoride vs. Cytomax click here thread got me thinking about it. I don't know the answer.

    Here's my question:

    If you put any high glycemic food/sugar into your blood while exercising, i.e. Gatorade, Bananas, Clif Bars, etc., shouldn't you have a corresponding low blood sugar episode shortly thereafter? Correct me if I'm wrong, but doesn't a sudden spike in blood sugar also cause a spike in insulin, AKA hypoglycemia? Wouldn't this cause a "bonking" effect?

    It would seem to me that high sugar foods would be counter-productive to endurance activities like biking where you spend a long time in the saddle. Am I missing something?

    Ever hear of glucagon? Your endocrine system doesn't just pump one hormone at a time. There are posiive feedback, negative feedback loops going ALL THE TIME as you're body is trying to maintain homeostasis.

    A spike in blood glucose will cause your body to increase insulin levels but it's not stupid enough (in the absense of pathology) to turn around and let you go into hypoglycemia which is a little more than low blood glucose.

    Give it a little more credit...
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  15. #15
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    Quote Originally Posted by Paul W.
    If you put any high glycemic food/sugar into your blood while exercising, i.e. Gatorade, Bananas, Clif Bars, etc., shouldn't you have a corresponding low blood sugar episode shortly thereafter?
    The insulin response is suppressed during exercise, thus you miss out on the sugar crash.

    Like Bontrager sez, give your body some credit...

  16. #16
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    if your sugar levle fell you would bonk out, yet the only time i bonked out was when i had hardly any food at all and no sports drink, only water.

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