by Marion Nestle
Jul 23 2007

Calories Defined

Today’s question is one I often get about my 15 seconds of fame in Morgan Spurlock’s film, SuperSize Me! (you can view the clip on my food politics website). A student in Great Britain writes: “…I would like to comment on your description of a calorie….You described it as “the amount of energy required to heat 1 litre of water by 1 degree Celsius.” Whereas I would argue that a calorie is the quantity of thermal energy required to raise 1g / 1cm3 by 1 degree Celsius, from an initial temperature of 15 degrees Celsius or 252 Kelvin. May I suggest that what you meant was a kilocalorie, and although this may seem pedantic, this is a gross difference and an inaccurate education for those watching. Especially after the number of people that were demonstrated to have no real understanding of the calorie…this was disappointing.”

My comment: Oh dear. It’s great that students are learning their basic chemistry but what I defined in SuperSize Me! was a Calorie (spelled with a capital C)–the kind used on food labels. This, of course, is really a kilocalorie. The calorie/Calorie/kilocalorie confusion is why I devote an entire chapter of What to Eat to explaining what calories are and why they matter.