As in weight per volume? I mean.. you always see them specified by weight but they have to have a volume, right?

I suppose different fat(for example) molecules would have different densities but then how do they universally have the same energy density? Are they converted to like a standardized type of fat? Thats the fat I'm interested in.

  • $\begingroup$ What is "standardized fat"? $\endgroup$ – M.A.R. Aug 8 '15 at 10:38
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    $\begingroup$ I get the sense you are interested in these compounds as they relate to dietary/nutritional science. Can you confirm/deny? That will help you get your question answered sooner. $\endgroup$ – Todd Minehardt Aug 8 '15 at 15:07

I assume the "energy density" you are referring to are the widely known statistics that:

  • fat contains 9 "calories" per gram (actually kilocalories)
  • protein and carbohydrates both contain 4 "calories" per gram

How can all fats contain "9" kcal per gram but have different mass densities? Here are a couple of reasons:

  • The 9 kcal/g figure is an approximation that assumes a typical dietary blend of fats. The figure would if considering chemically pure fat molecules.

  • The mass densities of most common fats doesn't vary that much. The densest "fat" molecules are probably the extremely short chain triglycerides like triformin and triacetin. They have densities of approx. $1.3~ \frac{\mathrm g}{\mathrm{cm}^3}$. These triglycerides have chain lengths of 1 or 2 carbons per fatty acid chain, a value far lower than common in natural fats. Triolein is more representative of dietary fats and has a density of 0.95$~\frac{\mathrm g}{\mathrm{cm}^3}$. So the mass density variation among different fat molecules is pretty small: a 30% increase is all that is really possible.


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