# Is a joule also known in nutrition as a kilojoule?

1. Dec 21, 2015

### 5P@N

I just came across Table 2 on pg 173 of "https://books.google.com/books?id=-rgoqmAF9icC&pg=PA159&lpg=PA159&dq=how+much+mass+would+a+snake+lose+before+it+starves&source=bl&ots=G89wh63BP9&sig=d6QmloQ3sMsOPS9PsPRzMd9s25I&hl=en&sa=X&ved=0ahUKEwj13Y6-2O3JAhVIJR4KHQ-VCyYQ6AEIJzAC#v=onepage&q=how%20much%20mass%20would%20a%20snake%20lose%20before%20it%20starves&f=false [Broken]". In the table, it mentioned that studied snakes had lost 55 grams of mass. It also mentioned that they had lost 976.9 "kJ".

Now: does the "kJ" mean kilojoules, or just joules? When I divide 55 by 976.9, I get: 17.75 "kJ" per gram. When I however look up elsewhere what the energy values in joules are for the variously mentioned classes of biological substances the author mentioned (carbohydrates, fats, and proteins), I discover that carbohydrates and proteins have 16.8 joules per gram, whereas fats have 37.8. A proportion of these substances would then form a figure of 17.75 joules, but not kilojoules. There's a difference here by a thousand-fold! Or is it that there's some idiosyncratic and arcane practice in biological sciences to call joules kilojoules? What am I missing here?

Last edited by a moderator: May 7, 2017
2. Dec 21, 2015

### Staff: Mentor

Those values are in kJ/g. See https://en.wikipedia.org/wiki/Food_energy

3. Dec 21, 2015

### 5P@N

So: 1 kJ = 1,000 J?

There isn't some sneaky joule v. Joule distinction as there is between the calorie v. Calorie, right? A joule is a Joule? A cigar is just a Cigar?

4. Dec 21, 2015

### 5P@N

I mean: the kJ as used in nutrition is the same kJ as is used in physics?

5. Dec 21, 2015

Yes.