Matt wrote about this here a bit. The short reply is: short term effects are often precisely the opposite of long term effects. This is why we see in every overfeeding experiment conducted that participants will not just gain and gain and gain indefinitely, but will hit a ceiling around 10 or 15% over their initial weight, which maks it incredibly hard to keep gaining. They become hypermetabolic, their energy levels increase, their hunger decreases, their transit time decreases, etc., as the body works hard to get back to the set point.
If overfeeding did cause insulin and leptin resistance, we would anticipate that it becomes easier as the experiment goes on for people to gain, not more difficult. The fact that it becomes increasingly difficult suggests a negative feedback loop, rather than a positive feedback loop.
Here’s another article on the Leningrad Hypertension Epidemic, illustrating again that short term interventions can sometimes produce precisely the opposite effects in the long term that they appear to produce in the short term.
Good points Rob. It’s important to be on the lookout for misconceptions such as these. We already know that overfeeding does not per se cause continuous weight gain or metabolic damage. There is cognitive dissonance there so sometimes simple intuition helps. Would nature have a built-in positive feedback loop of this sort? From an evolutionary standpoint, that doesn’t really make sense, so maybe the study’s authors missed something, and Rob hit it on the head.