A protein calorie question

[Paul Chefu]

Here's a question I've been wondering about.

Under normal metabolic conditions protein and carbohydrate are
converted to glucose before they can be utilized as fuel.
Different macronutrients are converted to energy at varying
efficiencies - the quoted average values are carbs and
proteins 4 kcal/g, fats 9 kcal/g.

Take an example of a person weighing 170 pounds with an LBM of
150. For weight maintenance he might require 2550 kcal per day
(15 x 170) and a minimum of 90 grams of protein (0.6 x 150).

Now, 2550 kcal could be made up from 150 g carbs, 150 g
protein and 150 g fat ((150 x 4) + (150 x 4) + (150 x
9)) = 2250.

Of the protein component 90 grams would be used for tissue
maintenance and repair leaving 60 grams for fuel. At a
conversion rate to glucose of 58% through de novo
gluconeogenesis, this would yield just under 140 kcal (60 x
.58 x 4). This is an apparent deficit of 460 kcal.

Is this deficit real, or is the amount required for tissue
repair already accounted for in the total caloric requirement
of 2550? Is protein burned directly at 4 kcal/g, regardless of
its conversion to glucose, without the intermediate step of
gluconeogenesis?

To put it another way, does the calorie count of
macronutrients take into account their differing energy
conversion efficiencies (i.e. is the quoted caloric value
gross or net). and how do other apparently
non-energy-generating uses of macronutrients affect the net
caloric content of a diet?

Paul

[Jay Tanzma]

Paul Chefurka wrote:

> To put it another way, does the calorie count of
> macronutrients take into account their differing energy
> conversion efficiencies (i.e. is the quoted caloric value
> gross or net). and how do other apparently
> non-energy-generating uses of macronutrients affect the net
> caloric content of a diet?

First of all, protein doesn't have to be converted to glucose
before its burned. Most of the amino acids you burn are just
broken down and burned, basically. It doesn't matter what the
immediate fate of the protein is either, be it structional or
for energy, because, eventually, all the amino acids you
consume (except the ones you die with, I suppose), are burned.

The 4 kcal/day figure is gross of any energy expended on
converting amino acids to glucose. This is an example of
"thermic effect," which is a component of total energy
expenditures. Typically, thermic effects account for about 10%
of total energy expenditures; however, protein is the most
thermogenic macronutrient (except possibly alcohol), so if
your client is on a high-protein diet, the total thermic
effect of his diet will be higher.

-Jay

[September]

Paul Chefurka <paul@chefurka.com> wrote in message
news:<3vas9u8bbb0rqavmta739ftebhc7f6iar0@4ax.com>...

> To put it another way, does the calorie count of
> macronutrients take into account their differing energy
> conversion efficiencies (i.e. is the quoted caloric value
> gross or net). and how do other apparently
> non-energy-generating uses of macronutrients affect the net
> caloric content of a diet?

You may find this site helpful:
http://asci.uvm.edu/nusc43/ener1.htm#METABOLIZABLE

[Paul Chefu]

On Mon, 25 Mar 2002 17:46:32 -0800, Jay Tanzman
<jtanzman@sph.llu.edu> wrote:

>The 4 kcal/day figure is gross of any energy expended on
>converting amino acids to glucose. This is an example of
>"thermic effect," which is a component of total energy
>expenditures. Typically, thermic effects account for about
>10% of total energy expenditures; however, protein is the
>most thermogenic macronutrient (except possibly alcohol), so
>if your client is on a high-protein diet, the total thermic
>effect of his diet will be higher.
>
>-Jay

Thanks, Jay.

Paul