There’s a pretty cool post over on Wise Geek of photos of 200 Calories’ worth of different foods, arranged in order by weight from least Calorie dense (you need a lot of it to get to 200 Calories) to most Calorie dense (just a little goes a long way).
It’s pretty interesting to see the range of quantities, and there are some counter intuitive examples–for instance, Coca Cola is up with the low density vegetables like celery and broccoli, which is confusing until you remember that, laden as it is with sugar, Coca Cola is still mostly water, which is completely devoid of Calories.
The post explains why they chose 200 Calories (it kept comparisons from getting too extreme) and why they chose the foods they did (they were convenient). It also rightly points out that, as the Coca Cola example shows, fewer Calories per unit of measurement doesn’t necessarily mean something is healthier–this says nothing about the nutritional content of these different foods. Just some interesting food for thought.