Myth: You are not supposed to say “calorie” you are supposed to say kcal or kilocalorie, otherwise you are not being precise. The following is a short and informal explanation explaining and debunking this myth.
For a very long time, nutritionists and everyone else who cares, have been using the tacit assumption that the term ‘calorie’ in casual conversation means kilocalorie. It would be ridiculous to talk about food energy in terms of single calorie units.
There are times, such as in a research paper, that this could cause confusion. It may be, perhaps, that single calorie units are being discussed (rarely). In these circumstances, the term kcal is used or Calorie with a capital C is used. And, of course, academic writing often uses inconsistent conventions and terminology.
As well, we often find that the term kilocalorie and calorie are used in the same bit of information to mean the same thing. Whichever you use, be consistent.
Regardless, if you use the word calorie it is usually understood that you are speaking in one-thousand calorie units as this has been understood for years and years.
Now, there is a problem with the calorie/kcal thing, but it is not in how we use these terms when we talk about nutrition or fat loss. It has to do with the fact that the calorie as a unit is not a part of the International System of Units or “SI”. The joule is the only energy unit that is part of the SI. The calorie is not. So if you want to be hyper-correct, you should be talking about food energy in terms of joules. Which means nobody will understand you.
Since you’re probably not going to do that, you can use the term calorie or kilocalorie, and as long as you are consistent at any one time, you will probably be understood. These problems are certainly there for science and for regulations on food labeling, etc. but they aren’t really a problem for most of us.