You need to eat vegetables everyday because you simply cannot find another food group that is as perfectly matched to our everyday human needs as vegetables! Vegetables fit us like a glove. From so many different perspectives, the nature of vegetables and the nature of human health are matched up in a way that simply cannot be duplicated by other food groups, including fruits, legumes, nuts and seeds, grains, seafoods, or poultry and meats.
To begin with, vegetables as a group are so low in calories that it is very difficult to gain weight even if you overeat them. (This statement wouldn't apply, of course, to batter-coated and fried vegetables, or to vegetables mixed into a thick cheese casserole.) On average, you are looking at 50 calories (or less) per cup from most of the World's Healthiest vegetables! That amount is astonishingly low, even when you compare it to other food groups within the World's Healthiest Foods. With the World's Healthiest nuts and seeds, for example, you're almost always looking at 750 calories or more per cup. That's 15 times higher than the World's Healthiest vegetables. With legumes, calories per cup fall into the 225-250 range. For fruits, the calories per cup can drop down fairly low for extremely watery fruits (like watermelon, which drops down to about 50 calories per cup), but it can also spike up to more than 400 calories per cup in the case of dried fruits like raisins. The uniquely low-calorie nature of vegetables as a group means that you can be generous with them in a Healthiest Way of Eating and not have to worry about the calories.