I don't have a reference, but I have a theory. I don't believe that simply being in a deficit works. When you eat less, hormones will tell your body to conserve energy and your expenditure will decrease automaticall. Your body protects the weight it's at. Eventually you will reduce to a point that you get a hormonal change that will adjust your setpoint and your metabolism will increase slightly and you will lose weight. Leptins are invloved in the maintenance of that set point. There is a lag between the reduction in calories and the metabolism slowdown caused by leptins. This is what I believe causes the step effect. You can take advantage of this by including refeeds into your diet. Bodybuilders have been doing this for years, essentially going low carb for a few days, followed by a refeed day, then repeat. This keeps your metabolism high and lowers your bodyfat setpoint at the same time.
I'm not sure but I expect Lyle MacDonald could be a good source for this. Here's his web site: http://www.bodyrecomposition.com/
Stephen Guyenet has been writing about setpoints lately. http://wholehealthsource.blogspot.com/