Multigrain and whole grain are not interchangeable terms. Whole grain means that all parts of the grain kernel — the bran, germ and endosperm — are used. In contrast, multigrain means that a food contains more than one type of grain; it doesn't tell you whether they're whole or refined grains, or a mix of both.
Whole-grain foods are a healthy choice because they contain nutrients, fiber and other healthy plant compounds found naturally in the grain. Look for products that list the first ingredient as "whole grain," "whole wheat" or "whole oats." Healthy adults should eat at least three 1-ounce equivalents of whole grains a day as part of a balanced diet.
from Katherine Zeratsky, R.D., L.D.