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What is the logic behind using calories as an energy unit in food?



 
 
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  #11  
Old August 5th, 2004, 12:38 PM
Lictor
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Default What is the logic behind using calories as an energy unit in food?

"andre a." wrote in message
...
The reason I am asking this question is the fact that calorie's
definition (1 calorie is the amount of energy necessary to increase the
temperature of 1g of water with 1 degree C) seems to refer to the
process of burning.


In scientific term, burning (as in, producing a flame) is just one of the
form energy liberation can take. The general process is oxidation and
reduction (redox). When you burn something in open air, what you actually do
is oxide the something and reducing the oxygen. For instance, 2H2 + O2 -
2H20. It's actually a transfer of electrons. The human body relies on a
number of redox reaction to use the energy from nutriments. The calorimeter
also relies on a specific redox reaction : combining things with oxygen (aka
burning).

Which brings some questions for me:
- isn't applying the same energy units to the body an
oversimplification? after all, the calorie unit seems to refer to a
simple thermodynamics system and not to a complex
bio-chemo-electro-psycho-mechanical one. we are not simply burning the
food - or we would probably be drinking kerosene.


It's not an oversimplification, because it's exactly the same. Burning and
metabolical process are both redox reactions. The first (or is it second?)
thermodynamic principle assess that whatever the chemical path from A to B,
the energy in the system remains the same. This means, there is no creation
or loss of energy, just transfer of it. So, the simple burning path is
energetically equivalent to the complex biological path. If you watch what
goes on with your lung, it's obvious : in goes O2, out goes CO2. All that
complex path actually amounts to burning something with oxygen and rejecting
carbon dioxide.

- how do we define the amount of calories in food? do scientists burn
every conceivable eatable substance and measure the heat?


Yes. Then, they substract stuff the human beings cannot digest (fibers).
This has been calibrated by putting human beings in large calorimeters, not
to burn them, but to measure their metabolism (influx of O2, output of CO2).

or, is the
measure based on the units of fat/sugars/etc. which have clearly
defined calorie amounts? (and, how are the calorie amounts in these
basic ingredients determined? burning and measuring heat?)


Some industrials use a calorimeter, but most recipes are calculated as the
sum of the calories of their base constituants.

- are calories from different eatable ingredients equal? obviously 1000
calories from sugar != 1000 calories from saturated fat != 1000
calories from lean beaf != 1000 calories from an overprocessed, salt-
and sugar- and preservative-packed fast food meal


Energetically, yes. Not difference whatsoever. Energy is energy. As long as
it can be digested, it's broken down into elementary constituants.

... even more, how will the body absorb 1000 calories from one basic
ingredient vs. 500 calories of sugar + 500 calories of fat (a
combination)? what about different combinations?


It will just break down the whole mess, until it has stuff it can burn, and
in the end, it will have an equal number of calories.
Note that we're only talking end product and energy! First, breaking down a
simple nutriment will be faster than breaking down a mix (especially with
fats, they tend to slow down things quite a bit). The total amount of energy
will be the same, but in the first case it will be available in a short
burst, while in the second it will be over a longer time. Also, our body
uses nutriments for other stuff than energy, like building and repairing
cells. From this point of view, the second case will be better, because the
body needs vitamins and fatty acids available in fat.

From all I've seen, the energy is being measured before intake. But

different bodies in different condition and level of health, age and
activity will absorb the same food in a different manner. Then wow can
one measurement unit be OK for everyone?


There is very little variation there, unless you have a really non standard
body or condition (obesity surgery to shorten the intestine, allergy to some
of the food, diarrhea, anti-sugar drugs, anti-fat drugs...). And even if
there are variations from one person to another, a given person will remain
fairly constant in her assimilation ratio.

Will a tomato organically grown from rich soil in a sunny
garden, provide the same amount of energy as one conventionally grown?


No, because the one grown in the rich soil and sunny garden will have more
calories A calorie table is only an average. In gives general orders,
like a tomatoe is rather low in calories, poor in proteins... But the
tomatoe grown in rich soil and high exposure to sun will tend to have a
higher sugar content. Likewise, if it lacked water, it will be more
concentrated and have higher sugar content. That's why wine is better when
it is on the side of the hill that gets the sun and on years that have had a
little dryness in the last weeks before the harvest : higher sugar content,
that will lead to more alcool. During the last year in France, with the very
high temperatures and dryness, some fruits (those that survived) had a 30%
higher sugar content for instance...
This has nothing to do with organic or not. It's just that food used to be a
living thing, and as such it has individual variations and depends on its
envirronment. If we feed you a sumo diet, you will be more caloric than the
average human being, because you will be fatter.


  #12  
Old August 5th, 2004, 04:20 PM
Heywood Mogroot
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Default What is the logic behind using calories as an energy unit in food?

"GaryG" wrote in message ...

1000 calories of sugar provides the same amount of energy to the body as
1000 calories from fish, brocolli, whatever. Our bodies digest them
differently, but the energy yield would be the same.


exactly? I highly doubt it. Whether or not there's a significant
difference is an interesting question, but it's rather naive to assume
that our complicated physiology is a linear system.

BTW - things like "chi" and "prana" are superstitions based on ancient
beliefs about how the body worked, but without any scientific basis
whatsoever.


things that come out of left field, outside of the western scientific
tradition, are not necessarily false by default though.

The concepts involved may be total bs, but the true scientific test is
how these alternative approaches obtain real world results; there may
be yet things to be learned from all these eastern and nativist
traditions.
  #13  
Old August 5th, 2004, 04:48 PM
GaryG
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Default What is the logic behind using calories as an energy unit in food?

"Heywood Mogroot" wrote in message
om...
"GaryG" wrote in message

...

1000 calories of sugar provides the same amount of energy to the body as
1000 calories from fish, brocolli, whatever. Our bodies digest them
differently, but the energy yield would be the same.


exactly? I highly doubt it. Whether or not there's a significant
difference is an interesting question, but it's rather naive to assume
that our complicated physiology is a linear system.


Granted...I think this would be an interesting area for research, but I
suspect the effective energy utilizations would be very close no matter the
source. Evolution has adapted our bodies to extract the maximum energy from
a wide variety of sources. One day our caveman ancestors might have
consumed nothing but meat from an animal they killed or found. Another day,
they might only eat a bunch of honey from a beehive they raided. Our bodies
have the ability to adapt to this and extract what they need from these very
different sources of energy.


BTW - things like "chi" and "prana" are superstitions based on ancient
beliefs about how the body worked, but without any scientific basis
whatsoever.


things that come out of left field, outside of the western scientific
tradition, are not necessarily false by default though.


Agreed. Unlike religious and magical beliefs, one of the hallmarks of
scientific thinking is that previously held beliefs can be challenged and
overturned. This, I think, is one of the fundamental strengths of the
scientific method. Unfortunately, it seems to cause consternation among
people looking for concrete answers when new knowledge replaces old.

The concepts involved may be total bs, but the true scientific test is
how these alternative approaches obtain real world results; there may
be yet things to be learned from all these eastern and nativist
traditions.


Studied, yes. Tested, certainly. But most of these ancient traditions have
had hundreds of years in which to prove their scientific validity, yet they
have not been able to do so. They live on as religious beliefs, taken on
faith alone, but are unable to "obtain real world results".

GG


  #14  
Old August 5th, 2004, 06:35 PM
andre a.
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Default What is the logic behind using calories as an energy unit in food?

Thank you for all the replies.

To recap:
Conclusion 1. the energy in foods is indeed measured by burning them in
calorimeters, substracting what [is believed] the body can not absorb.
Energy in foods is measured in kilo (thousands-of-) calories, not
calories.

Questions:
a. Why is this unit used for the human body? What is the background for
this choice? I understand that questioning such a widely accepted
practice sounds ignorant and will greatly appreciate replies containing
answers (vs judgement).

b. How is the energy spending measured in the body? We have all seen
those charts: 30 minutes of running equal X (kilo)Calories, 30 minutes
of swimming equal Y, etc. How is this measured? Also, it is very
illogical for me to have one measure for everyone - what about a 300 lb
untrained body vs a 160lb trained athlete? What about running in the
hot summer vs running in the cold winter. (see Jamie's post for more
sensible allocation of calorie intake. I say these factors vary wildly
from person to person, in different conditions)

My opinion is that this unit is accepted for its convenience rather
than its relevance and is a step into the direction of treating the
human body as a machine which it is not. I am looking for the science
behind it because I want to have a more educated opinion.

Conclusion 2. There is no [measurement of] nutritional difference
between organic vs conventionally grown/raised food. Conventional
pesticides are less dangerous than organic ones. Organic food is more
likely to be contaminated with bacteria.

Note: Forget the "chi" theory - it was just a suggestion for an
alternative viewpoint. There is however an obvious difference in the
texture and taste of organic vs non-organic food. There is obvious
difference between a healthy free-range chicken and a bird leading
agonizing existence in a small cage, force fed "nutritional" mix
containing the remains of other birds, hormones and antibiotics. There
is a measurable biochemical change in an animal's body if it suffers
when killed.

Based on the comments above I presume there is no (popular) scientific
method of measuring the "vitality" of food - by that I mean the
possibility to have 2 foods make a person "feel" different and have
different levels of vitality despite the foods' identical nutritional /
vitamin value. Seems that to food science the nutrition value of food
is determined by its content, period.

Thank you.
-- Andre

  #16  
Old August 5th, 2004, 08:25 PM
Lictor
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Default What is the logic behind using calories as an energy unit in food?

"andre a." wrote in message
...
a. Why is this unit used for the human body? What is the background for
this choice?


Because the human body is a thermodynamic machine. At least, as far as
energy is concerned. Once the experiences proved that, it was logical to use
common unit to measure energy at the time of discovery. It's used so
commonly that the correct internationnal unit, kJ (kilo-joule [sp?]) never
managed to get widespread use.
The whole theory was proven by Lavoisier in 1770, up to then, it was
believed that the stomach was some kind of furnace. Lavoisier proved that in
fact it was a slow combustion, that was down continuously and *chemically*.
Then, Laplace and him managed to calculate the basal metabolism and the
energy spent by some physical activities... So, it's not exactly modern
history The first calorie tables date back to the 19th century.

b. How is the energy spending measured in the body?


It's a chemical reaction, we know its inputs (some nutriment and oxygen) and
its outputs (energy and CO2 and some oxidated nutriment). So, if you measure
the "visible" inputs and outputs (through a mask for instance), you can tell
how much energy was used. Another solution is to use a huge calorimeter, not
to burn the patient, but to measure how much energy he produces.It's a bit
tricky to build, but people managed it in the 19th century.

We have all seen
those charts: 30 minutes of running equal X (kilo)Calories, 30 minutes
of swimming equal Y, etc. How is this measured?


Same way as above.

Also, it is very
illogical for me to have one measure for everyone - what about a 300 lb
untrained body vs a 160lb trained athlete?


Any decent chart takes body weight into account.

What about running in the
hot summer vs running in the cold winter. (see Jamie's post for more
sensible allocation of calorie intake. I say these factors vary wildly
from person to person, in different conditions)


Well, it's the same matter with the calories from food. The table only give
you an approximation. So, you know that rollerskating burns more calories
than playing golf. Likewise, a calorie table tells you that on average, an
apple is worth x calories. But the particular apple you're going to eat
might be worth x+30% or x-20%. By definition, when you build a tool like
this, you work with averages. The only way to know *your* values would be to
hook *you* to a calorimeter.
That's why I have always been very dubtfull about calorie counting diets...

My opinion is that this unit is accepted for its convenience rather
than its relevance and is a step into the direction of treating the
human body as a machine which it is not.


Yes, it's a step in treating the human body as a thermodynamic machine. In
itself, it's not false, until you push it to its limits. Kind of like
Newtonian physics vs Quantic Physics. Newtonian physics works well, most of
the time. From a strict weight gain/loss, the human body *is* such a
machine, though each human being seems to have its own efficiency at
converting excess calories to fat.
However, eating is more than calories. Eating is a social habit, it's a
emotional issue, a cultural trait... A successful diet has to take all that
into account, but at the end, all that will matter is the calories in and
calories out. The whole difficulty of the diet is how to get the brain which
is in command to feed the proper amount to the thermodynamic machine it's
mounted on...

Conclusion 2. There is no [measurement of] nutritional difference
between organic vs conventionally grown/raised food.


There is, if you look at vitamins and the like. Though it's not really
organic vs conventional, it's all a matter of what you want to produce :
quantity or quality. Sustainable agriculture try to find a decent middle
ground in that equation for instance. Using conventional when it's not
harmfull and organic when it really adds quality.

Conventional
pesticides are less dangerous than organic ones.


It's more like conventional is not automatically bad and organic is not
automatically good.

Organic food is more
likely to be contaminated with bacteria.


Same. It all depends on how it's done. It's like "traditional bread". If
your baker is incompetent, it will be only bad quality traditional bread.
People tend to think of quality when they hear "traditional". Here, it only
means you get to see the guy who baked that awful bread face to face

There is however an obvious difference in the
texture and taste of organic vs non-organic food. There is obvious
difference between a healthy free-range chicken and a bird leading
agonizing existence in a small cage, force fed "nutritional" mix
containing the remains of other birds, hormones and antibiotics.


Yes, that's organoleptic differences. Doesn't change the calories much, but
food is more than calories, it's also emotions and feelings. And yes, a
chicken that tastes good will be a lot more filling than a tasteless one -
to your brain. The brain integrates a lot of elements before issuing the
"satisfied" signal : caloric value, taste compared to previous memories,
emotions (like my mom used to bake!)... That's why this kind of food might
feel more "filling" to you.
And it's really not organic vs non-organic. It's using quality species vs
productive species, feeding it quality stuff... If the industry was willing
to improve quality, it would have a lot of room to do so inside the current
production system. Likewise, if your organic producer were using the same
species of chickens the industry uses, I doubt he would manage to produce
anything worth it.

There
is a measurable biochemical change in an animal's body if it suffers
when killed.


That's why you let meat rest before selling it. Red meat takes about one
month to reach you...

Based on the comments above I presume there is no (popular) scientific
method of measuring the "vitality" of food - by that I mean the
possibility to have 2 foods make a person "feel" different and have
different levels of vitality despite the foods' identical nutritional /
vitamin value.


It's called psychology. It's a soft science, but it's still a science. Some
products, like wine, have been extensively studied on that matter. Some diet
approach also take all that into account. As my nutritionist told me: "You
feed both your body and your brain. Your body is satisfied with calories,
your brain is satisfied with emotions. If one of the two is lacking, your
hunger is not fully satisfied". Calories deal with feeding your body,
they're a good measure of that...


  #17  
Old August 6th, 2004, 06:01 PM
Doug Freyburger
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Default What is the logic behind using calories as an energy unit in food?

andre a. wrote:

To recap:
Conclusion 1. the energy in foods is indeed measured by burning them in
calorimeters, substracting what [is believed] the body can not absorb.
Energy in foods is measured in kilo (thousands-of-) calories, not
calories.


Correct.

Questions:
a. Why is this unit used for the human body? What is the background for
this choice? I understand that questioning such a widely accepted
practice sounds ignorant and will greatly appreciate replies containing
answers (vs judgement).


Because it's a reasonable approximation that works most of the time.
If you keep your protein/carb/fat ratios in the middle of the range,
weight gain and loss is somewhat linear with calories eaten. It is
easy to measure and works much of the time.

On the one hand this leads some folks to falsely conclude that "a
calorie is a calorie is a calorie" because when they only look donw
the middle it tends to look that way.

On the other hand this leads other folks to figure out ways to
exploit loopholes where types of calories matter. Both low carb
and low fat exploit such loopholes. Loss can happen on these
plans at calorie levels that would trigger maintenance if your
percentages were down the middle.

b. How is the energy spending measured in the body? We have all seen
those charts: 30 minutes of running equal X (kilo)Calories, 30 minutes
of swimming equal Y, etc. How is this measured? Also, it is very
illogical for me to have one measure for everyone - what about a 300 lb
untrained body vs a 160lb trained athlete? What about running in the
hot summer vs running in the cold winter. (see Jamie's post for more
sensible allocation of calorie intake. I say these factors vary wildly
from person to person, in different conditions)


Ultimately it's measured by having someone hooked into an oxygen
system and measuring their O2 input and CO2 output. But most of
the time it's measured the way electric motor output is measured
and sure enough that isn't right.

In the end, models of calories burned like the one on Fitday are
terrible approximations.

My opinion is that this unit is accepted for its convenience rather
than its relevance and is a step into the direction of treating the
human body as a machine which it is not. I am looking for the science
behind it because I want to have a more educated opinion.


Calories for intake are a good approximation most of the time.
Calories for exertion are a bad approximation most of the time.
You can always find exceptions.

Conclusion 2. There is no [measurement of] nutritional difference
between organic vs conventionally grown/raised food. Conventional
pesticides are less dangerous than organic ones. Organic food is more
likely to be contaminated with bacteria.


There is no difference in macronutrients protein/carb/fat, but
that doesn't mean there aren't differences in trace minerals.
But trace minerals are much harder to measure.

Based on the comments above I presume there is no (popular) scientific
method of measuring the "vitality" of food - by that I mean the
possibility to have 2 foods make a person "feel" different and have
different levels of vitality despite the foods' identical nutritional /
vitamin value. Seems that to food science the nutrition value of food
is determined by its content, period.


Correct.
 




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