So the mechanism as I understand it is like this: - high glucose in bloodstream causes insulin release - insulin tells cells to burn glucose rather than fat for energy consumption, but also triggers fat takeup (blood to storage) - ergo fat + glucose in your blood will cause you to store fat - sucrose is half glucose and half fructose - fructose is metabolized only in the liver, and into fat. Fructose - it's argued - was relatively rare in paleo times, so we don't really handle it as well as glucose and fat - ergo, if you consume sucrose (glucose+fructose), *half* of your calorific intake (the fructose) will be converted into fat, because the other half (glucose) is triggering insulin release
Now clearly if after you come down from your glucose high you starve yourself into ketosis, then you'll burn the fat back off. But if it's not that long till your next sucrose-laden meal, then that's not going to happen - ketosis takes *three days* to kick in. And because all those calories from the fat were mopped up out of the bloodstream, you only got to burn half of your meal off. So you start feeling hungry. Taubes makes the point that it's not that overeating causes obesity, but that obesity causes overeating: fat and starving.
