How the Calorie Content of Food is Determined

Scott 13
Ken J. asks: How is the calorie content in food determined?

nutrition-labelFirst, let’s make sure everybody here understands what a calorie is. A calorie is just a measurement of energy- the amount of energy needed to raise 1 gram of water 1 degree Celsius at standard atmospheric pressure. This makes sense when talking about calories in food. Food provides energy and our bodies need this energy to function throughout the day. I’m hoping to burn about 100 calories while writing this response. If not, this 100 calorie snack pack won’t be as health conscious as I thought and will go straight to my hips!

Second, it’s also important to note that Calories in food are actually measured in kilocalories, so 1000 actual calories for every 1 Calorie listed.

Manufacturers used to measure calories using a “bomb calorimeter”. This process involved placing the food source in a sealed container filled with water. They would then burn the food with electrical energy. After the food had completely burned up, they would measure the water temperature to see how many degrees it was raised and thus how many calories used.

In 1990, under The Nutrition Labeling and Education Act of 1990, the FDA began requiring food manufacturers to label the amounts of nutrients and calories contained in their products. This act resulted in moving away from the bomb calorimeter method for determining the number of calories in food. One reason for this was to make it easier and less expensive for manufacturers to meet the standard. Another was that the bomb calorimeter method measures all available calories in the product. Since most foods contain indigestible components, like fiber, that pass through our system and get excreted in the form of bum brownies, this would lead to a consistent overestimation of ingested calories using the bomb calorimeter. Instead, they used an easier method known as the Atwater system.

This approach adds up the calories available through the energy containing nutrients in the food item, like protein, carbohydrates, fats, and alcohols. They use standard reference tables for common ingredients based on their energy densities.  Things like 4 kilocalories for proteins, 4 for carbohydrates, 3 for organic acids, 9 for fats, and 7 for drinkable alcohols (ethanol). No wonder all that beer gives me this soft belly! It has over 1.5 the calories per mass as proteins and carbohydrates (well worth it though).

So for a specific example, let’s say that tasty snack you have before you jump on the treadmill contains 5g of protein, 10g of carbohydrates, and 15g of fat. The label on the package would then read 225 Calories (or 225,000 calories for those who can’t stand over simplification which results in misconceptions!)

If you liked this article and the Bonus Facts below, you might also like:

Bonus Facts:

  • Nutrient labels on food products in the United States list their percentages based on a 2000 calorie per day diet. This can be somewhat misleading. Energy requirements can vary significantly based on your age, sex, weight, height, physical activity, and base metabolic rate, ranging on average between 1000-4000 calories. The Merck Manual states 1,600 calories per day are needed for young children and sedentary women; 2,000 for active adult women and sedentary men; and 2,400 for active adolescent boys and young men. These values are also somewhat arbitrary because the average person uses different amounts of energy almost daily. One day you might go for a hike and the next sit on the couch watching football. One month you could lose 5 pounds and increase your base metabolic rate in the process. The next month with the same caloric intake gain 10 pounds and decrease your base metabolic rate. The point being, you should make an attempt, at least once or twice a year to figure out your daily caloric needs. This will help you in determining the amount of food you should eat. Or not… You could always just say “Wal-Mart makes that shirt in extra large, so I’m good!” The “see-food” diet as it were- you see food, and then you eat it!
  • Joey Chestnut, the current world record holder for hot-dog eating, ate 68 hot dogs and buns in 10 minutes. At 290 calories per dog, that’s 19,720 calories in 10 minutes! That’s about the energy the average person uses in 10 days! The current hot dog eating record for a woman is held by Sonya Thomas. She ate 40. Let’s hope she works out like Michael Phelps before his retirement. He reportedly was burning approximately 12,000 calories per day while training.  One assumes unless he’s changed his eating habits drastically, he’ll be quite the tubby man soon enough.  This wouldn’t bode well for his ability to keep Subway as a sponsor. :-)

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13 Comments »

  1. Fred F January 2, 2013 at 10:05 am - Reply

    No apostrophe in plurals – you spelled “calorie’s” but it should simply be “calories”.

    • Daven Hiskey
      Daven Hiskey January 2, 2013 at 1:51 pm - Reply

      @Fred F: Yep. *shakes fist in general direction of typos*

  2. Rajeev January 2, 2013 at 10:44 pm - Reply

    Your example above, with 4g of protein/10g of carbs/15g of fats, adds up to 195 calories, not 225.

  3. Ed M. March 27, 2013 at 7:48 pm - Reply

    Some carbohydrates are not metabolized (e.g. corn kernals) but do oxidize completely in a bomb calorimeter. How is thsi accounted for? (By the way, as pointed out earlier, the total is 195 Calories in the example cited.)

  4. Dougie December 6, 2013 at 11:00 am - Reply

    Doesn’t tell me how many calories are in a slice of homemade cake

  5. Phil December 13, 2013 at 12:21 pm - Reply

    if you put Gin in a bomb calorimeter filled with water how do you burn the gin?

  6. Valas February 17, 2014 at 11:45 am - Reply

    Bahahaha.. bum brownies! I’m going to use that one.

  7. Carl February 19, 2014 at 5:26 am - Reply

    I did the math several times and arrived at 195 calories. Did I miss something in the below copied info?

    Things like 4 kilocalories for proteins, 4 for carbohydrates, 3 for organic acids, 9 for fats, and 7 for drinkable alcohols (ethanol). No wonder all that beer gives me this soft belly! It has over 1.5 the calories per mass as proteins and carbohydrates (well worth it though).

    So for a specific example, let’s say that tasty snack you have before you jump on the treadmill contains 5g of protein, 10g of carbohydrates, and 15g of fat. The label on the package would then read 225 Calories (or 225,000 calories for those who can’t stand over simplification which results in misconceptions!)

  8. Manna September 22, 2014 at 6:52 pm - Reply

    Our bodies could not give a rats a** about caloric value. What they need is nutritional intake and usable ingredients. n°1 substance in our bodies is collagen next is elsasten look them up. Then look up how our body metabolizes these compounds then burn your calorie books for ever.

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