Actress Heather Graham ("The Hangover"), NFL Hall of Famer Jerry Rice (who was a receiver for the 49ers), and former NBA player DeJuan Wheat (was with the Timberwolves and Grizzlies) all sport names of well-known grains. But are they 100% whole?

We'll leave that answer to movie critics and sports commentators. But we do know that when it comes to ascertaining the whole-grain content of various foods, most people score way below 100%.

A study published in the journal Public Health Nutrition found that when presented with mocked-up grain products, 31% of U.S. adults incorrectly identified the healthier options for cereal, and 47% goofed regarding bread.

When estimating the whole-grain content of real products, 43% overstated it for honey wheat bread and 51% for 12-grain bread.

Why does this happen?

Mostly because of intentional misdirection on the packaging, according to researchers from Tufts Friedman School of Nutrition Science and Policy. Use of words like "multigrain," "whole grains," and "12-grain," as well as packaging that's brown or has an official-looking "whole grain" stamp, is most likely to cause consumers to mistakenly think the food contains healthy ingredients.

Unfortunately, none of those "signals" tell you the product contains 100-percent whole grain and nothing but that grain.

The researchers point out that 42% of Americans' calories come from low-quality carbohydrates, so it's important to know if you're getting minimally processed or unprocessed grains. Those kinds of grains can help prevent or reverse diabetes, obesity, heart disease, high blood pressure, and some cancers.

Only go for products that say "100% Whole Grains," and read nutrition and ingredient labels.