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.
Optimal nourishment is another reason that vegetables are important on a daily basis. You need to eat vegetables everyday because you need a supply of vitamins everyday. Some vitamins can be stored for future use and others cannot. Some of the vitamins that can be stored in the body are called fat-soluble vitamins such as vitamins A, D and E. For the body to run its best we also need water-soluble vitamins. Found within this group are all of the "B-complex" vitamins, including vitamins B1, B2, B3, B5, B6, B12, biotin, choline, folic acid, and vitamin C. We need these water-soluble vitamins every single day because they can't be stored in the body or can only be stored in small amounts. And since the body cannot make these vitamins (or any vitamins), we have to get them from the food we eat. When considered as a group, vegetables are unusually rich sources for a full mixture of water-soluble vitamins. That's why so many health care recommendations (including the U.S. Food Pyramid) encourage 3-5 servings of vegetables per day.
When it comes to vegetables, there is also their abundance of phytonutrients to consider. In the science of food, no change has been bigger than the discovery of phytonutrients and their unique place in our health. Phytonutrients include all of the unique substances that give foods their brilliant colors, their delicious flavors, and their unique aromas. They are also the nutrients most closely linked to prevention of certain diseases. Carotenonids and flavonoids are the two of the largest groups of phytonutrients, and there is no food group that provides them in amounts as plentiful as vegetables. The phytonutrients in cruciferous vegetables like broccoli, and in root vegetables like onions and garlic, are unique when it comes to decreased risk of certain cancers, and some of these phytonutrients simply cannot be found in other food groups.
Finally is the pleasure of chewing and amazing digestive benefits that come from the high-fiber content of vegetables. Dietary fiber is critical for our health, not only on a daily basis, but on a meal-by-meal and snack-by-snack basis as well. Food cannot move through our digestive tract in a healthy way unless it is fiber-rich. And, vegetables are some of the very richest sources of fiber that exist.