Current standards for classifying foods as “whole grain” are inconsistent and, in some instances, misleading, according to a new study released by the Harvard School of Public Health.

Researchers found that grain products with the Whole Grain Stamp, a widely-used front-of-package symbol, were higher in fiber and lower in trans fats, but also contained significantly more sugar and calories compared to products without the Stamp.

Along with the Stamp, researchers assessed four other industry and government guidelines for whole grain products — any whole grain as the first listed ingredient; any whole grain as the first ingredient without added sugars in the first three ingredients; the word “whole” before any grain anywhere in the ingredient list; and the “10:1 ratio.”

From two major U.S. grocers, researchers identified 545 grain products in eight categories, and collected nutrition content, ingredient lists and the presence or absence of the Whole Grain Stamp on product packages from all of these products.

The study also determined the American Heart Association’s standard proved to be the best indicator of overall healthfulness. Products meeting a ratio of total carbohydrate to fiber of less than or equal to 10-to-1 were higher in fiber and lower in trans fats, sugar and sodium, without higher calories than products that did not meet the ratio.

The study, “Identifying whole grain foods: a comparison of different approaches for selecting more healthful whole grain products,” appears in the Jan. 4 advanced online edition of Public Health Nutrition.