The scientific explanation suggests that slowly digestible carbs (whole grains) don't spike insulin levels the way white flour, sugar, refined carbs, and fruit juices (and alcohol) do. Sugary Chinese food is notorious for satisfying hunger for about an hour and then you hit the leftovers. When insulin spikes, blood sugar decreases, and one then feels the need to eat again to get the blood sugar level back up starting the cycle all over again.

But here's the thing...carbs are fairly calorie intensive and portion control must be exercised or you're going to gain weight. Personally speaking, if I get on a sandwich kick (even using whole grain, healthy bread), I find myself eating more and more frequently. Bread in all forms satisfies hunger but only temporarily. And I can eat a wheel barrel full of whole wheat pasta - enough of it until I'm sick-full, and two hours later I want another helping of spaghetti (or whatever).

It may be genetic. I know runners, for instance, don't usually have to worry about carbs because they burn it off. But I have to avoid or limit carb intake or I balloon up in no time. It isn't that way for everyone, but it is definitely that way for me.

And that USDA pyramid is well-known bullshit. Twelve servings (even half-cup servings) of grains a day? Can you say "wheat lobby?" I'd weight 500 lbs. if I followed its recommendations.