Re: % cal from xxx...


"MMu" <brilhasti@xxxxxxx> wrote in message
news:424a851c$0$10836$3b214f66@xxxxxxxxxxxxxxxxxxxxxx

> as i stated before: the ammount of calories needed a day can be estimated
> for a person of given sex, age and bmi. therefore saying "recommendations
> are x% of every macronutrient on total energy intake" is not irrational at
> all and allows rough comparison of various food patterns to the
> macronutrient recommendations.
Since all macronutrients are NOT oxidized to completion (all C -> CO2,
all H -> H2O) in human digestion, and they are in the process (Parr Bomb
Calorimeter) by which caloric contents are measured, the -theoretical-
energy possible from *complete combustion* from each is -never- realized.
If one wants to "estimate", it is not necessary to run the estimates
through an arithmetically-absurd paradigm, simply just estimate pro, fat,
cho needs on a gm/pound bodyweight basis.

> example#1 ... total bogus.
Since there are an infinite number of 'foods' with radically-differing
wt% compositions that produce -identical- PCF profiles, the latter are
useless and obscure the absolute amounts consumed. Thus, choosing 'foods'
based on PCF profiles that are identical to the 'target' profile will very
likely not choose 'foods' with identical nutrient profiles. Biochemistry
works on grams of material, not internal ratios of irrelevant entities.

> the relative numbers give information about how much the food fits or does
> not fit the recommended food composition.
If there an infinite number of 'foods' that have the same PCF profile,
and they do not have the same composition, the PCF profile is useless as a
quantitative tool.

> example#3:
>
> [quote]
> If we have a certain food with, say, 10% of calories as protein, how much
> of this food should we eat to get 20 grams of protein?? There is NO way
> to calculate this, since the absolute amounts of all nutrients are
> irreversibly lost when one goes from true weight percent to "percent of
> calories from ..."
> [end of quote]
>
> how about:
> calories of food[per 100g] * 0,1 / 4 kcal/g = xx g Protein[per 100g food]
First, you are indiscriminately identifying cal and kcal as the same,
but what is a erroneous factor of 1,000 between friends??
Then, you do not know the total number of calories in the food, just
that 10% of an unknown number of calories is that hypothetically from
protein.

> xxg Protein in 100g equals 20g Protein in ?g
> I will leave calculating the ammount of food for 20g protein to you.
Why, can't you do it? Of course not, you have one equation in two
unknowns: "xx" and "?", no one can solve that. Thanks for illustrating my
point, though.

> 50% (w/w) water
> 10% (w/w) carbohydrates
> 20% (w/w) protein
> 15% (w/w) fat
> 5% (w/w) minerals/ash
>
> with this info you cannot tell how many grams of protein you have either.
> you need the weight.
Just as you needed the total amount of calories, but did not have it, in
the previous example. Interesting, you just ignored that when you did it.
However, taking arbitrary amounts of several different foods with this
w% profile will allow one to easily maintain the target w% composition,
while taking arbitrary amounts of several different foods with identical PCF
profiles will not. That is the point you missed in Example #1.

Laurie


.

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