An interesting animal (NB. not humans) study is out this month showing that eating certain types of fat may disrupt healthy or ideal appetite control/regulation.  The brain may not regulate your hunger like it should.   Expect more work in this area, and in the meantime, don’t stop eating fat.  Just keep an eye on portions and try to choose the healthier fats.

View a synopsis here: http://www.sciencedaily.com/releases/2009/09/090914110533.htm.

http://www.sciencedaily.com/releases/2009/08/090829092042.htm

ScienceDaily (2009-08-29) — Scientists have identified cells in the stomach that time the release of a hormone that makes animals anticipate food and eat even when they are not hungry. The finding, which has implications for the treatment of obesity, marks a landmark in the decades-long search for the timekeepers of hunger. The work reveals what the stomach “tells” the brain.

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So it’s not just willpower or environment or any one thing.  Hormones certainly play a part.