Prevention's "Eat More, Lose More" diet plan suggests that you get three to four servings of whole grains a day—up from the American average of one—to stay full longer so you don't overeat. Plus, you will boost your energy in significant and noticeable ways.

First, a definition: Whole grain foods include oatmeal, whole wheat bread, brown rice and wheat germ. Many processed cereals are made with whole grains, but check the package ingredient list to be sure.

The best rule of thumb: "Whole grains contain at least two grams of fiber per serving, and you can find that on the label," says Joanne Slavin, a professor of nutrition at the University of Minnesota.

Whole grains can be slimming if you up your intake of fiber to at least the recommended 25 to 35 grams a day. According to Tufts University researchers, weight-loss potential is higher in people who eat whole rather than refined grains, probably because high-fiber foods keep you feeling full longer.