It's commonly accepted in the obesity research community that fat gain causes insulin resistance and an increase in circulating insulin, and that this is a major reason why obese people usually have insulin resistance and high circulating insulin. Part of the rationale is that substantial fat loss by almost any means improves insulin sensitivity and causes circulating insulin to decline, and substantial fat gain from deliberate overfeeding causes insulin sensitivity to decline and circulating insulin to increase. I recently cited three references to support this contention on another blog, and was challenged, so I decided to revisit these references to make sure I had understood them correctly (1, 2, 3). Since I took the time to do this, I figured I may as well write it up for my readers, since these studies are quite informative.
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