I recently posted on Calorie Density by Food Label. It introduced the concept of Calorie Density and gave some examples of how to use it. The challenge is that this method is quite tedious and unmanageable when used in real life - who is really going to check each item every time?
Some clever people have taken the info and adjusted it for food groups. They have applied it to broad categories to give you helpful directions. When food is not very calorie dense you can be far less careful about consumption level. When it is very calorie dense you have to be extremely careful about how much you consume.
When you look at the picture for this post you see the categories and some other info. Far left is calorie light, and portion control is not much of an issue - just get a balance of lots of different fruits and veggies to get the best balance of nutrients (which are mostly on the right side, by the way!). Left side is calorie dense - much easier to overeat. Nuts/Seeds and Oils do have some nutritional value so the point is not to totally avoid the far left side, but just eat in appropriate portions. And if you mix veggies (a salad) with oils (a dressing) and pour the dressing on liberally, you've moved the salad way over to the left side of the picture.
Here are three pictures that give some different looks at calorie density:
Calorie Density Basic Groups. (described above).
Calorie Density Breakouts. This looks at some experiments they did. When people ate food that was less than one calorie per gram, they lost weight no matter how much they ate (ate till they were full). When they ate till they were full from food that was between one and two calories per gram they lost weight if they were generally active (30-60 minute per day), with less likely to lose if not active and more likely to lose if more active. If they ate till they were full from food that was between two and three calories per gram, everyone gained weight except for elite athletes. If they are till they were full from food that was over three calories per gram, everyone gained weight, even elite athletes.
Calorie Density Target Average. Aim for about 1.2 Calories per gram on average and you'll be in good shape. In simple terms that means eat mostly from the green categories on the left and sprinkle in nutrient rich food from the far right. You would do best to go light on meatand avoid refined/junk food altogether or atmost very occasionally.