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How do they figure out the number of calories in a recipe?

How the Food Industry Calculates Calories
This label on a package of cereal shows how many calories (really, kilocalories) are in one serving.
This label on a package of cereal shows how many calories (really, kilocalories) are in one serving.
Joe Raedle/Getty Images

You may have noticed a lot of restaurants suddenly listing calorie counts on their menus or signage. In November 2014, the U.S. Food and Drug Administration (FDA) required chain restaurants, grocery stores serving prepared foods, vending machines with 20 or more locations and other food providers to post calorie counts on their menus and menu boards by Dec. 1, 2016 [source: Federal Register]. But how are these places coming up with their caloric information?

There are a number of private companies that analyze food samples to determine their caloric count. One, QC Laboratories in Pennsylvania, charged $700 per sample in 2014 if customers wanted the item independently tested to determine its calorie count and other nutritional information. If clients only wanted a simple calorie count via the use of a standardized database, the price was $150 to $200. In the latter instance, food providers may find it easiest to do the work themselves. All they need to do is add together a menu item's calories, then divide by the number of servings [source: Samuelson].

A quick example is a simple PBJ sandwich. According to the USDA's National Nutrient Database for Standard Reference, the calorie counts are:

2 slices of white bread: 154 calories

2 tablespoons peanut butter: 191 calories

1 tablespoon jelly: 56 calories

Total calories: 401

If the above sandwich is served in a half-sized portion, it would contain 200.5 calories. The only hitch to this system is that databases use average calorie counts for their foods — for instance averaging the calories in Skippy, Smuckers and Jif creamy peanut butters to come up with a calorie count for "creamy peanut butter" — so they're not 100 percent accurate. Because of this, food providers sometimes prefer to pay for the pricier independent testing [sources: Samuelson, Schechner].

Yet even if a restaurant has every menu item tested, calorie counts can still be a little off. Researchers from Tufts University tested foods from 42 restaurants in a 2011 study, and found 20 percent actually contained 100 more calories than advertised. Most of the undercounting was on the items labelled as "diet" or "light." Other foods actually contained fewer calories than advertised [source: Avila and Marshall].

In general, the researchers found that fast-food places have more accurate calorie counts, as much of their food is prepackaged and created in a formulaic style. Sit-down restaurants, where dishes are prepared individually, have more problems with accurate calorie counts. It's easier for portion size to differ slightly when each dish is made by hand, and often by different people.