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Guru Kate: How are calories in food measured? Guru Graphic - Illustration by Casey Kleeb Full view

Guru Kate: How are calories in food measured?

Illustration by Casey Kleeb

In the past 100 years, the primary method of measuring calories has not changed course. The Atwater method uses classical knowledge about how food is metabolized via fats, protein and carbohydrates.

According to this system, there are nine calories per gram of fat, four calories per gram of protein, four calories per gram of carbohydrate and seven calories per gram of alcohol.

Then, food companies identify the amount of carbohydrates, fats and protein in their foods and add together the total amount of calories. Fairly simple process, yes?

Nope. Back when Wilbur Olin Atwater pioneered the technique of respiration calorimetry, it was breaking science. Previous experiments had only been conducted on animals, but thanks to Atwater, we learned what food calories meant in human terms.

The math equations and methods have simple roots. Metabolized energy is equal to gross food energy minus whatever is secreted (via feces, urine, gas, et cetera).

However, current availability of subjects and advanced technology calls for an overhaul of this ancient experimental basis for these commonly understood values. According to Martin Wickham of Leatherhead Food Research, these standard caloric values can be reestablished.

Wickham also says that in the past 100 years, we have learned that different foods have different structures.

One example of this is plant verse animal foods. Plant foods have cell walls that take extra energy to break down. However, their fats, protein and carbohydrates are treated the same as these macronutrients that come from animal sources in the Atwater system of calorie prediction.

In a study conducted by Janet Novotny, Sarah Gebauer and David Baer in July 2012, the researchers found a 32 percent overestimation of calories coming from almonds using the Atwater technique compared to laboratory experimentation of human metabolism.

Knowing that there can be such a huge discrepancy between food labels and what we actually get out of food can seem unsettling. However, eating correct portions and focusing on consuming necessary vitamins and minerals is what truly leads to a balanced diet.

Fussing about calories here and calories there is a stressful practice, and unless you have access to a metabolism laboratory, it will be impossible to determine the precise amount of calories in everything you eat.

It is unlikely that there will be an overhaul on food labels; the good still inherent in the Atwater model outweighs manpower and the price it would take to investigate each food’s honest caloric contribution.

Written by Kate Lindsley

Kate Lindsley is the columnist for Guru Kate. She is currently a Junior in her Dietetics program and has been writing for TNL since January of 2011. Her hobbies include cooking, knitting and running with friends. She also really enjoys questions submitted to Guru Kate, and may even answer them in print!