Is a joule also known in nutrition as a kilojoule?

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Discussion Overview

The discussion centers on the relationship between joules and kilojoules in the context of nutrition and energy values of biological substances. Participants explore whether the "kJ" mentioned in a specific study refers to kilojoules or joules, and how this relates to the energy content of carbohydrates, fats, and proteins.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether "kJ" in the study refers to kilojoules or joules, noting a discrepancy in energy values when comparing mass loss of snakes to energy content of biological substances.
  • Another participant clarifies that the energy values for carbohydrates and proteins are actually in kilojoules per gram, not joules.
  • There is a query about the equivalence of joules and kilojoules, specifically whether 1 kJ equals 1,000 J, and if there is a distinction similar to that between calories and Calories.
  • Participants express a desire to confirm that the kilojoule used in nutrition is the same as that used in physics.

Areas of Agreement / Disagreement

Participants generally agree on the conversion between joules and kilojoules, but there is some confusion regarding the context in which these units are used, particularly in nutrition versus physics. The discussion remains unresolved regarding the specific application of these units in the referenced study.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about energy values and the potential for misinterpretation of units in different contexts.

5P@N
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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 ". 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?
 
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5P@N said:
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.
Those values are in kJ/g. See https://en.wikipedia.org/wiki/Food_energy
 
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?
 
I mean: the kJ as used in nutrition is the same kJ as is used in physics?
 
5P@N said:
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?
5P@N said:
I mean: the kJ as used in nutrition is the same kJ as is used in physics?
Yes.