If a person is trying to lose weight, grains, starchy vegetables, and legumes should be limited to only 2-3 servings per day. A serving would be 1 slice of Ezekiel bread, 1/2 of an English muffin, 1/2 of a burger bun, 1 of my muffins, 1/2 cup rice or quinoa, and about 1/2-1 cup of cereals (depending on the type of cereal). Potatoes, yams, and winter squashes should be about 1/2 cup after cooking. Beans and lentils are the same--1/2 cup after cooking.
Someone who is very athletic would probably need more, however most people do not expend enough energy daily to need more than 2-3 servings per day.
One note to make is that grains, starchy vegetables, and legumes should be varied throughout the day. And wheat should not be eaten every day either. The standard American routine of toast for breakfast, a sandwich on bread for lunch, and a roll for dinner is WAY TOO MUCH WHEAT.
A better routine would be an oat bran muffin for breakfast, brown rice for lunch, and a sweet potato for dinner.
No one ever asks how many vegetables they should be eating! That would be 4-6 cups per day.