Many consumers believe that foods labelled with fat claims (e.g. low fat) are lower in calories than comparable regular foods and are therefore helpful for weight management. However, it is unknown whether such foods are actually lower in calories. Our aims were to determine 1) the relative proportion of foods carrying fat claims among various food categories within the Canadian marketplace; and 2) whether foods with fat claims are actually lower in calories than comparable foods without claims. The Food Label Information Program 2010, a database of Canadian foods developed at the University of Toronto, was used to compare the calorie content of products with and without fat claims within a given food subcategory, as defined by Schedule M of the Food and Drug Regulations. Median differences of 25% or greater were deemed nutritionally significant, as that is the minimum difference required for comparative claims such as “reduced” and “lower” in the Food and Drug Regulations. Fat claims were present on up to 68% of products in a given food subcategory. Products with fat claims were not significantly lower in both fat and calories compared to comparable products without fat claims in more than half of the subcategories (24 out of 40) analyzed. Conversely, in 16 subcategories, foods with fat claims were at least 25% lower in calories; however, for many of these foods, the absolute difference in calories was small, i.e., for 9 of the 16 subcategories, the absolute difference between foods with and without fat claims was <50 calories, even though the relative percent difference was high. This research suggests that foods with fat claims may be misleading consumers and undermining their efforts to manage body weight or prevent obesity.