Thread: Where does 1 pound = 3500 calories come from?

Originally Posted by Krelian

I've heard the claim on a number of occasions that you have to "eat 3500 calories in excess to gain a pound".

Where does this come from, and does it actually have any basis in fact? Given that a calorie is a unit of energy and a pound is a unit of force, it doesn't seem like they could be interconvertable.

hm...calorie is a unit of energy yes, but it can be thought of as potential energy, as it releases energy when broken down, it can also be stored. That is just a guess....heh, I'm sure someone else will have a better, more scientific explanation.

I should have said that the pound was a unit of mass. So I looked it up, and the units for a calorie are kg * m^2 / s^2. And the units for pounds could be thought of as kg (since you just multiply a pound by a constant factor to get a kilogram). It doesn't seem like you can multiply a quantity with units of kg by a constant factor to get a quantity with units kg * m^2 / s^2...

Just to be fancy, a pound is a unit of force. You were right the first time. Even though americans use the term for mass, it is not. SI states kg is the mass quantity.


There is no direct conversion between kg and energy, you need to come up with a conversion factor based on the amount of energy per unit of kg..

ie 1gram fat = 9 cal = 37.66 Joules

1lb=453grams * 9 cal/gram = 4077 cal

Theoretical value of cal/lbs

This is covered in any freshman chemistry book. The real question is I need to verify the validity of 9cal/gram of fat. Im sure this is an average.

Originally Posted by nsimmons

...
Theoretical value of cal/lbs

This is covered in any freshman chemistry book. The real question is I need to verify the validy of 9cal/gram of fat. Im sure this is an average.

The heat of combustion for lipid varies with the structural composition of the triglyceride molecule’s fatty acids. For example, 1 g of either beef or pork fat yields 9.50 kcal, whereas oxidizing 1 g of butterfat liberates 9.27 kcal. The average caloric value for 1 g of lipid in meat, fish, and eggs equals 9.50 kcal. In dairy products, the calorific equivalent amounts to 9.25 kcal per gram and in vegetables and fruits, 9.30 kcal. The average heat of combustion for lipid equals 9.4 kcal per gram.

...One can round the average net energy values to whole numbers referred to as Atwater general factors. These values, named for Wilbur Olin Atwater (1844–1907), the 19th-century chemist who pioneered human nutrition and
energy balance studies at Wesleyan College, indicate the net metabolizable
energy available to the body from ingested foods. If precise energy values for experimental or therapeutic diets are not required, the Atwater general factors provide a good estimate of the energy content of the daily diet.

ATWATER GENERAL FACTORS
• 4 kcal per gram for dietary carbohydrate
• 9 kcal per gram for dietary lipid
• 4 kcal per gram for dietary protein

(source: Sports & Exercise Nutrition, McArdle, Katch & Katch)

Good to know. Thanks!

Nice post GG

Originally Posted by IainDaniel

Nice post GG

Thanks - I thought it was pretty interesting "nutrition trivia", since most of us tend to get the facts from sites like this one (IM). Good to know the origin of the numbers we throw around day in and day out on here!

To add to the trivia - protein, in a bomb calorimeter, has 5.65 kcal/gram, but in the body, the nitrogen component does not get oxidized. It combines with hydrogen and is excreted as urea, so protein ends up with a net energy value of 4.6 in the body.

just cool nerdy stuff to know...

Im not trying to get smart or anything, but how the hell do you know that, does it apply to your job or do you just know a lot about nutrition

Originally Posted by JasnoE

Im not trying to get smart or anything, but how the hell do you know that, does it apply to your job or do you just know a lot about nutrition

Well, in this particular case, i typed this up from a book i am studying for my graduate degree, but i do hold lots of random nutrition info in my head. Probably not so much as Trouble might (not even close), but a good amount.

I am working on my masters degree in nutrition science and also preparing for the CISSN exam this fall.

Originally Posted by JasnoE

Im not trying to get smart or anything, but how the hell do you know that, does it apply to your job or do you just know a lot about nutrition

studying....it is a beautiful education.


*cue music*

"The more you know"