When looking to get lean, you have to eat methodically by timing your nutrient intake. Eating the wrong thing at the wrong time can stop you losing those last few pounds. In my experience with myself and others around me it takes a little planning to get below 12% body fat.
To easily explain this I will oversimplify the different nutrients:
Protein = Recovery Carbs = Fast Fuel Fat = Slow Fuel Fibre = Filler
You can see on the graph that carb and fat intake go down from day to night, as we need less energy in the evening (so we are likely to store it). So take in your carbs early (or before/after training), cutting out the carbs as the day goes on, and reducing fat intake towards the night.
Protein is needed in all meals, as recovery is always happening. Intake is raised at night firstly because you must compensate for the lack of carbs, but mainly because most of the bodies muscular recovery is done while asleep (protein is the building block).
Fibre is taken in to help digestion, and to help you feel full (vegetables etc). Fibre is heightened at night due to the reduction in carbs/fat (if needed)