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Nutrition Diet, supplements, weightloss, health & longevity

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Old 04-13-2004, 05:49 AM   #1
Cliff Stamp
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In "Fats that heal, Fats that Kill", it is stated that the rate of fat absorption in the small intestine is about 10 g per hour. Does anyone know what the rates are for the absorption of proteins and carbs? Can you simply estimate it from the fat absorption rate factoring in the difference in digestion times (5-7 hours for fats, 3-5 for proteins, 2-3 for complex carbs, 0.5 for simple ones).

I ask because I am interested in glycogen loading after resistance training. What I would like to know is how to calculate the amount of glycogen depleted and could this be restored by just the normal meals or would they not provide the nutrients fast enough. Calculating the glycogen depleted is also problematic. Any references or suggestions on how to do that. It is trivial to calculate the raw energy needed, but at what efficiency does your body obtain this, how much glycogen is used in the process.


-Cliff
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Old 04-13-2004, 10:52 AM   #2
Robert Wolf
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Cliff-
See if you can track Paul Kayley down for some info on this topic. The post workout nutrition thread had some interesting info along this line as well.
Robb
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Old 04-14-2004, 01:49 AM   #3
Paul Kayley
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Cliff check out this thread

http://www.crossfit.com/discus/messages/23/3460.html

See if there is part of an answer in there for you
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Old 04-14-2004, 10:29 AM   #4
Robert Wolf
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My instinct on this is that intestinal absorption is never a limiting factor. Insulin spill over and the partitioning of nutrients towards fat is the real issue however.
Robb
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Old 04-14-2004, 01:57 PM   #5
Paul Kayley
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I agree with you Robb. The body is very efficient at absorbing and storing unused energy..... any of the nutrients absorbed (absorption rate will vary depending upon many intestinal factors, including size, health, enzyme density, bacterial density, etc...we're all different) and in the blood stream will be stored at varying rates depending upon hormonal environment, current glycogen status in the liver and muscle cells, current intramuscular triglyceride stores, and so on. Basically if you over-supply in either rate or total amount the body will be forced to store as fats. 'Drip feeding' will meet all your nutrient needs best, however when recovery takes greater priority over fat-burning, it may pay to take advantage of increased insulin sensitivity during and following intense exercise. Using insulin in this way does not agree with everyone, nor does everyone agree with its practice! However, I am most interested in maximising sports performance. Anyway, as far as I am aware most evidence warning against the dangers of elevated insulin relates to people outside of the exercising or post-exercise state. Could talk more but going to sleep.....its getting late here in blighty...ZZZZZZ
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Old 04-15-2004, 07:13 AM   #6
Cliff Stamp
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The main reason I ask is that I have seen studies which claim that resistance training can promote calorie burning of ~100 calories / min (food calories of course). At this rate of expenditure I can't see the body being able to provide for it with digestion because the rate at which you would need to be able to absorb food would be much too high. I also have not been able to find the efficiency ratios for the three main fule pathways in the cell (phosphagen system,glycolysis,oxidative phosphorylation). I remember reading a year or two back that creatine phosphate cycling was really inefficient, ~4%, which seems reasonable as it has to provide energy very fast. but can't track down where I read it to, it was on usenet somewhere.

-Cliff
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Old 04-15-2004, 08:28 AM   #7
Brian Hand
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Cliff, that 100 cal/min rate must be for the duration of a heavy set, not the average for the workout! Ultimately your aerobic capacity is going to limit the average rate of expenditure for the workout to something much lower than this. The actual rate is going to vary tremendously, depending on things like exercise selection, lactate threshhold, poundages, rest between sets, a million variables.

Calculating glycogen depleted is also going to be nearly impossible. Even if you find a chart that says this activity is x% glycolyitic, y% oxidative, z% phosphagen, the numbers will be estimates or averages, different people will burn at different rates, and the same person will burn at different rates on different days, depending on diet, metabolic adaptations, hormone levels, again a million variables.

I'm sure that anyone who wants to can eat enough carbs to replenish glycogen. As a rule you can eat a lot faster than you can run. I have used cyclic ketogenic diets and I found that one day of eating like they're shooting me at dawn was more than I needed to replenish carbs.

I think we are stuck with crude measures, just keeping tabs on blood sugar, performance, and body comp. to determine how much carb is enough.
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Old 04-15-2004, 09:06 AM   #8
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Yes, it was just for the activity. But even assuming for example you can work for half the time you are in the gym, and are only one half of the ability of the individuals tested, this still gives you like 1500 calories an hour, which seems really high to me. Even if you rest a lot more, working only 25% of the time and resting for 75%, the numbers are still really high, 750 calories an hour (well more because of the increased metabolic activity during resting).

-Cliff
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Old 04-15-2004, 10:51 AM   #9
Brian Hand
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Cliff, I think you are extrapolating an awful lot from that number. Over the course of an hour, everything is going to catch up with you metabolically. Irrespective of the activity, you aren't going to burn (many) more calories in an hour than your cardiovascular system can support. Most strength sessions don't even approach that rate of energy expenditure.
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Old 04-16-2004, 07:15 AM   #10
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Yes, that is what I assumed from just basic common sense. If this was the case you would never do cardio to lose weight. However while a lot of work has been done on calorie burning during cardio little seems to be done on heavy resistance training.

-Cliff
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