Ratings of foods can be presented as
- an overall summary score or
- a threshold (see Table 2-1).
A threshold rating system uses cutoff values to determine whether a food meets specified nutrient criteria. Often there is one set of criteria used to determine whether the system receives the rating, and the rating is often displayed as an icon such as a check mark. Some systems use several threshold levels for a graded rating system, such as the Guiding Stars, which rates foods with none, one, two, or three stars.
Systems that use an overall numerical score, such as the Nutrient Rich Food Index and NuVal systems, rate all foods on a continuum. For example, the algorithm for the NuVal system, which is called the Overall Nutrient Quality Index, scores foods from less than 1 to a large finite number but then converts the scores to 1 to 100 for consumer use. Threshold systems use nutrient criteria to determine if a food receives a rating, which is often a pictorial icon such as a check mark. An example of a threshold system is the Ofcom Nutrient Profiling Model, which uses ratings of healthy and less healthy. Icons are popular on FOP and shelf labels because they are graphic and "eye catching." The food receives an icon if it meets specified nutrient "thresholds." Icons usually represent a dichotomous condition, either the food product meets the criteria or it does not. Some systems use multiple ratings with the icon (e.g., Guiding Stars provides either no star or one to three stars based on different nutrient thresholds for each star).
Threshold systems generally categorize foods as good or bad, whereas numerical scoring systems do not. Some nutritional professionals believe there are no bad foods and that it is overall dietary intake that is important; therefore, they criticize threshold schemes that label foods as "bad." Another criticism of the use of thresholds to determine a rating or whether a food qualifies for an icon is that the cutoff values are chosen somewhat subjectively because there is no absolute scientific basis for them.