Whole grain foods are supposed to be 100 percent healthy, right? Well, not always.

A recent study by Harvard School of Public Health found that although some grain products proudly display the Whole Grain Stamp on their packages, they also contain significantly more sugar and calories compared to products without the Stamp.

To make things even more confusing, no single standard exists for defining any product as a "whole grain". So how do you distinguish healthier whole grain products from the not-so-healthy ones? The ingredient list is always a giveaway. Here's what to look out for:

Look for whole grains listed as the first ingredient, without added sugars in the first three ingredients. Sugar that is listed high on the list of ingredients means that the product is laden with it.

Look for the 10:1 ratio. Ensure that the ratio of total carbohydrate to fiber is equal to 10 to 1 or less, which is approximately the ratio of carbohydrate to fiber is whole wheat flour. Products meeting this ratio were higher in fiber and lower in trans fats, sugar, and sodium, without higher calories than products that did not meet the ratio, say the researchers.