A commonly referenced "fact" is that a caloric surplus of 3500 kcal is equivalent to a 1 lb gain in bodyweight. But I'm confused. If you get 3500 kcal worth of, say, fatty acids, which are 9 kcal per gram, then that's about 390 g, which is just under 0.86 lb. How can you gain 1 lb of bodyweight from eating a surplus of less than 1 lb? Am I missing something?

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    $\begingroup$ Probably water. $\endgroup$ – Bryan Krause May 9 '17 at 20:07
  • $\begingroup$ Also, although there are problems with the 3500kcal equals 1 pound rule, even when it works, the point isn't that eating 3500kcal adds a pound of bodyfat: rather, catabolizing 1lb of body fat equals about 3500kcal of energy. $\endgroup$ – Bryan Krause May 9 '17 at 20:12
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    $\begingroup$ agree with @BryanKrause above concerning water... however, the way you have phrased the "fact" mentioned above is not entirely correct, which is a common misconception - it costs some energy to store energy in the body. In other words, even though 3500 kcal is ~1 pound thermodynamically, that does not translate into exactly one pound of body weight gain. To store energy as lipid, the body "spends" some of the energy to package and store it as lipid. Thus, if you gain a pound, you've actually eaten more than 3500 calories. (Note: the 3500=1 pound is hotly debated, etc) $\endgroup$ – Vance L Albaugh May 9 '17 at 20:13
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    $\begingroup$ @VanceLAlbaugh Thanks, you explained a bit more thoroughly than I did. Also: proof that it is easier to lose a pound than to gain one! Call the daytime TV 'doctors'! (all a joke, of course...) $\endgroup$ – Bryan Krause May 9 '17 at 20:47

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