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Why the calories on a label never add up
Times the protein and carbs by four and the fat by nine, and you almost never land on the number at the top. Nobody is lying to you.
Conner KadziolkaUpdated 3 min read
Pick up almost any packet in your cupboard and try it. Times the protein by four, the carbs by four and the fat by nine, add them up, and you'll usually miss the number printed at the top. It's easy to think somebody got it wrong.
Usually nobody did. An AI helped me dig into why, and every fact below links to a source at the bottom. The sum on the back of a label is a shortcut, and three things knock it off.
in short
Calories on a label rarely match protein times 4, carbs times 4 and fat times 9, because those factors are rounded averages, fibre counts as about 2 Calories a gram instead of 4, the label rounds its numbers, and your body does not absorb every calorie in some foods, such as almonds.
Four, four and nine came out of that room
Atwater taught chemistry at Wesleyan University in Connecticut, and the USDA calls him the father of modern nutrition research in the United States. Besides the room, he burned food in a steel "bomb" sitting in water and measured how much the water warmed. His numbers came out at about 4.1 Calories for a gram of protein and 9.3 for a gram of fat. Labels round those to 4 and 9, give carbs 4 as well, and Canada's food inspectors still use them, with 7 for alcohol. He also worked out that a pound of turnips holds 139 Calories, which is a lot of turnip.
The label is doing sums you can't see
In Canada, fibre is counted inside the carbohydrate line, but it isn't worth 4 Calories a gram. The CFIA tells food makers to count it at 2, and the fibre in wheat bran at just 0.6. A packet with 10 grams of fibre can print 20 Calories fewer than your sum, and the label is still right.
Then the label rounds. The CFIA's own worked example takes a macaroni and cheese at 447 Calories and prints 450. The grams on a label are rounded too, so a sum built from them was never going to come out exact.
Our labels go the other way. Our Athens Almighty Chicken Souvlaki lists 35 grams of protein, 40 of carbs and 30 of fat, and 140 plus 160 plus 270 is 570, the number on the label. Our kitchen rounds the grams first and prints the calories as the plain 4, 4 and 9 sum of them, so you can check it at the table.
AvailablePlant-BasedYour body is not a copper room
The 4, 4 and 9 rule assumes you absorb everything you eat. Some foods don't play along. USDA researchers fed people measured diets with and without almonds and worked out how much energy their bodies really kept. A serving of almonds gave 129 Calories, not the 168 to 170 the factors predict, which is 32 percent fewer. Walnuts came in at 146 Calories an ounce, 21 percent under. Whole raw almonds were 25 percent over their label maths and chopped roasted ones 17 percent, so how a nut is cut and cooked changes what you get from it.
So when a label's sum comes up short, check the fibre line first and allow for rounding. The rest belongs to a chemist's averages and a body that leaves a little of every almond behind.
Sources
- 1IEEE Spectrum, Atwater's copper calorimeter, the bomb calorimeter, his 4.1 and 9.3, and turnips at 139 Calories a pound
- 2USDA AgResearch, Atwater as the father of nutrition research, the 4, 4 and 9 system, and the almond and walnut studies
- 3CFIA, elements of the Nutrition Facts table, The 4, 4, 9 and 7 factors, fibre at 2 Calories a gram, wheat bran at 0.6, fibre inside carbohydrate, and the 447 to 450 example
- 4CFIA, nutrition labelling compliance test, Every label value is a rounded number standing for a range
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