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Many nutrients consumption recommendation come in % of calories per day.

  • One should not get more than 30% calories from protein to avoid kidney overload ;
  • One should get around 30% calories from fat ;
  • etc.

But then comes fibers.

I searched the USDA recommendations, googled much. Some articles say around 30g per day is good. Some say more. But nowhere did I find an upper limit, even if consuming too much of it exposes yourself to flatulence, bloating and abdominal cramps. Anyway, those articles considered the middle-aged man on a regular, 2000 kcal diet, not the athlete.

I eat much more than the recommended amount: around 80g a day. But then, I'm on a bulking diet and eat 4000 kcal a day. I do not eat specific food like All-bran and alikes. I eat a good proportion of fruits and vegetables, but not like crazy either. My guess is fibers should come proportionally to daily calories, and 80 might just be the right number for me.

How minimum and maximum daily fiber intake should be calculated ?

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A link to the article with the maximum would be good as otherwise I'd say: why do you care? Anyway, if you don't feel that there is anything completely wrong with your nutrition and don't feel obvious side effects (like bowel pain or heavy gas) I'd say you really shouldn't care. Especially because I don't get why there should be a maximum, what isn't needed simply gets through untouched. Btw I am not 100% sure if this question is on topic, as the relation to exercise is only marginal. –  Baarn Oct 24 '12 at 14:09
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@Informaficker: «what isn't needed simply gets through untouched» — this is a dangerous assumption. I am seeing it quite often on the internet and I am not sure where it comes from, but it contradicts reality: people who eat more than they need become obese. –  Mischa Arefiev Oct 24 '12 at 14:43
    
If this statement was made in relation to fiber consumption, then it is partially true: very little dietary fiber is processed by human bowels, if any. –  Mischa Arefiev Oct 24 '12 at 14:46
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@MischaArefiev It was made in relation to fiber consumption and regarding this question, where weight gain and muscle bulking seems to be the target not a hindrance. Of course the statement is not always true: "I don't need that arsenic, so it will just pass through" would be a good example. –  Baarn Oct 24 '12 at 14:57
    
Too much fiber leads to all kind of evils, as I added to the question : fitday.com/fitness-articles/nutrition/healthy-eating/… –  Gabriel Oct 24 '12 at 15:22
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1 Answer 1

Even the bullet points you enumerate early on are arguable for various people. For diabetics, you absolutely want a greater amount of calories from protein and fat - taking in 40% of your calories by carbohydrates is too many for a diabetic's damaged endocrine system to handle. For athletes, the distinction becomes even more complex. What sort of athletes are we talking about? Endurance athletes, like marathon runners? Pure power athletes, like olympic weight lifters? Or some sort of mix of the two, like baseball or rugby players? I cannot imagine a weight lifter trying to source 40% of their energy off carbohydrates - there's just no way they'd take in enough raw material to replace the massive damage their training regimen does to their muscles.

We also need to be clear on the type of fiber we're talking about. Digestible fiber comes from your wheat breads, your all-bran, etc. This fiber can be broken down by your system, but will generally not provide you a huge amount of nutritional benefit. It is mostly used for working out the 'net carbs' in a food by subtracting them from the overall carb count. Indigestible fiber comes mostly from vegetables, and some fruits like apples. This is the fiber that helps seal and slick your gut to make digestion of everything else much easier.

Digestible fiber is very useful for cutting regimens and helps maintain a good gut flora environment, but generally people get plenty of it and it's not a concern. Proper consumption of indigestible fiber relates directly to overall digestive health, so it's basically always a concern.

The reason, I think, you did not find an upper limit is that most of the theoretical problems from consuming too much fiber basically solve themselves. Overconsuming digestible fiber will mean your body spends too much time breaking down the stuff that doesn't provide it much nutrition. Your body will respond to this by inducing an acute craving for what it requires, and you will not feel satisfied until you satiate it. Overconsuming indigestible fiber could theoretically coat your gut too thickly to absorb micronutrients that your body needs (such as vitamins) from a normal concentration of it. However, the vegetables you'd have to consume to accomplish this are so rich in these micronutrients that you're going to have a much higher concentration in your gut, anyway! Here is a good article with a fiber overview and a decent number of cited sources for further reading if you want it.

As always, for active people the #1 thing is to focus on your macronutrients. Getting worried about things like this is a great way to get off track and miss the forest for the trees. It's a great question, but its overall impact on your physical fitness, particularly with regard to training, is not going to be anywhere near as great as getting the right mix of protein, carbs, and fats in your diet for your training plan.

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Although your claims sound reasonable, I'd be much more happy if they were supported by some references. –  Baarn Oct 28 '12 at 20:33
    
@Informaficker What precisely do you want referenced? The function of digestible/indigestible fiber? The mechanics behind eating them? Focusing on macronutrients? The reason I am confused is because all of these things are among the most basic lessons out there when understanding nutrition. I'm happy to provide some references, but if I were to equate this to mathematics, your request is coming off as asking me to cite references that 10 + 10 actually does equal 20. –  YYY Oct 29 '12 at 15:02
    
Last year I had to prove in my math class that 1 is greater than 0. Although it seems to be obvious it has to be done. But anyway, some reference (or a Wikipedia link) on fiber coating the guts etc. and hindering nutrition intake would be nice. –  Baarn Oct 29 '12 at 15:15
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@Informaficker That's well and good but I doubt you had to prove anything like that in Algebra 1! Anyway, I edited in a decent overview article from the NYTimes with plenty of further reading sources if you want it. I'd point out that I said the 'hindering' part was theoretical (there's never been any studies on that to my knowledge), but I was amused to find that the NYTimes article puts forth pretty much the same philosophical guess, with the same justification as to why it's not a concern. –  YYY Oct 29 '12 at 15:34
    
I saw it too late, but you are linking to the same article already linked in the question ;) –  Baarn Oct 29 '12 at 17:41
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