There was a study released last week that basically stated the same thing. Refined grains, potatoes and meat attribute to greater weight gain vs diets centered around vegetables. It's really looking like the best meal ecologically, economically and for your health is one where the primary calories come from vegetables.
It is true that fats are among the most calorie dense food in existence but that doesn't make them necessarily 'practical'. If animal fats have lots of external costs (in terms of environmental damage) then they aren't very practical. The costs are just not well understood.
As for the spinach straw man argument...I don't think anyone is suggesting that you eat 10 kilos of spinach, that would be extremely unhealthy. I think the OP was suggesting simply that calories come mostly from plants. This includes nuts (peanut butter is very high calorie), fruits (also high calorie) and vegetables.
If you allow "plants", then yes- starchy staples, nuts, fruits all have you covered on calories. It's up to the OP though to clarify whether he meant plants or celery.
Dietary cholesterol has not yet been shown to be harmful.
Some well-researched books on the subject include "Fat and Cholesterol are good for you" by Uffe Ravnskov and "The Great Cholesterol con" by Anthony Colpo.
High levels are correlated with atherosclerosis and cardiovascular disease, but they haven't been shown to cause those conditions. Some cholesterols are also "good" (high density) in that they have positive effects for people with high cholesterols -- they can lower levels.
