How do they measure the caloric content of food?

[Derleth]

(Or 'Caloric', if you must.)

I assume they can't just use bomb calorimeters; they likely derive it from tables of ingredients to some extent but that doesn't actually answer the question so much as shoves it across the plate a bit.

So how is it done in general?

[Bill Door]

Why would you assume they didn't use bomb calorimeters? It's the right tool for the job.

[AaronX]

Bomb calorimeters are not as accurate since even indigestible things like fiber is flammable. I think the most accurate methods use enzymes to mimic digestion.

[guizot]

Are you referring to measurement in general, or of a specific sample?

[Michael63129]

I don't think they need to burn the food in its entirety (which, as mentioned, will also burn indigestible parts); if you know how much fat, protein and carbohydrates there are and the calories given off when they are burned, then you know how many calories are in the food.

[DSeid]

"Cecil's" answer:

they measure calories in food the old-fashioned way — they burn it. At least they did years ago, in a wonderful device known as a bomb calorimeter ... Researchers don't use calorimeters much today because years of experiment have reduced calorie calculations to a simple formula: protein and carbohydrate each have four calories per gram and fat has nine, regardless (more or less) of what food it's found in. ...

(From way back in 1992.)

SciAm's answer concurrs:

The original method used to determine the number of kcals in a given food directly measured the energy it produced.The food was placed in a sealed container surrounded by water--an apparatus known as a bomb calorimeter. The food was completely burned and the resulting rise in water temperature was measured. This method is not frequently used today.

The Nutrition Labeling and Education Act of 1990 (NLEA) currently dictates what information is presented on food labels. The NLEA requires that the Calorie level placed on a packaged food be calculated from food components. According to the National Data Lab (NDL), most of the calorie values in the USDA and industry food tables are based on an indirect calorie estimation made using the so-called Atwater system. In this system, calories are not determined directly by burning the foods. Instead, the total caloric value is calculated by adding up the calories provided by the energy-containing nutrients: protein, carbohydrate, fat and alcohol. Because carbohydrates contain some fiber that is not digested and utilized by the body, the fiber component is usually subtracted from the total carbohydrate before calculating the calories.

Actual calories delivered to the body may be different yet as some foods are not completely digested above and beyond the fiber component ... but that is another issue.

(Google is my friend.)

[HoneyBadgerDC]

I would starve someone till they had no more poop. Then make 2 indentical dinners. One I would burn and the other I would feed the subject. When the subject took a poop I would burn his poop and subtract that from the dinner I burned.

[The Second Stone]

I was told 30 plus years ago by my high school physics teacher that they used a bomb calorimeter to determine food calories.

[KarlGauss]

Are the calorie counts provided by the manufacturer subjected to checks by gov't regulators? And, of course, I mean more than just checking the manufacturer's arithmetic for the components given. In other words, are the percentages (fat/carbs/protein) verified? Likewise, is the fiber content confirmed (since exaggerating its amount would permit a significant subtraction of the weight to be deducted from the 'net' calorie count)?

Thanks!

[Tangent]

Originally Posted by badger5149

I would starve someone till they had no more poop. Then make 2 indentical dinners. One I would burn and the other I would feed the subject. When the subject took a poop I would burn his poop and subtract that from the dinner I burned.

Science!

[guizot]

Originally Posted by KarlGauss

Are the calorie counts provided by the manufacturer subjected to checks by gov't regulators? And, of course, I mean more than just checking the manufacturer's arithmetic for the components given. In other words, are the percentages (fat/carbs/protein) verified? Likewise, is the fiber content confirmed (since exaggerating its amount would permit a significant subtraction of the weight to be deducted from the 'net' calorie count)?

I've always wondered about this. What percentage of packaged food products actually get inspected and analyzed as a matter of routine? It's one thing for the numbers to add up on paper, but who's going to know if the relative amounts they put into the package are changed? What if, for example, 5 grams of fat secretly get exchanged for 5 grams of carbs? Simply weighing the package isn't going to tell you what changed, but the total calories will be different.

[Ambivalid]

Originally Posted by KarlGauss

Are the calorie counts provided by the manufacturer subjected to checks by gov't regulators? And, of course, I mean more than just checking the manufacturer's arithmetic for the components given. In other words, are the percentages (fat/carbs/protein) verified? Likewise, is the fiber content confirmed (since exaggerating its amount would permit a significant subtraction of the weight to be deducted from the 'net' calorie count)?

Thanks!

Originally Posted by guizot

I've always wondered about this.

+1.