Given the low caloric density of most plant foods, that also implies that carb calories will need to be low on an optimal diet. (perfecthealthdiet.com)
In fact, it's not easy to get 50 % of your daily calories from fruits and vegetables because of the high bulk and low caloric density of fruits and salad vegetables. (paleodietfoodlist.net)
Eating lots of beans which are generally higher in caloric density will also do this and is a good approach. (nutritionfacts.org)