The science (and limitations) of measuring nutrients
Burning food to measure energy
How we measure calories: burn food and measure the heat released
Step 1: Food sample placed in chamber
A dried, weighed sample of food is placed in the steel "bomb"
130 years old and still on every label
The Atwater factors, created in the 1890s, are still used on every nutrition label
Protein
4
cal/gram
Carbohydrates
4
cal/gram
Fat
9
cal/gram
Alcohol
7
cal/gram
The FDA allows up to 20% variance. Some foods are even further off.
Why the variance?
Database Lookup
Most companies use USDA FoodData Central to look up values for ingredients
Calculation
Add up all ingredients using the 4-4-9 Atwater factors
Lab Testing (Sometimes)
Only required if making health claims. Most labels are never lab-verified.
Rounding
FDA has specific rounding rules (calories round to nearest 5 below 50, nearest 10 above)