Methodology for Adding Heme Iron and Non-Heme Iron to a Food and Nutrient Database and Dietary Analysis Software

Including both heme and non-heme forms of iron in food and nutrient databases is important because they differ in bioavailability and potentially have differential health impacts.

The study describes the methodology used for assigning heme and non-heme iron values to foods in the University of Minnesota Nutrition Coordinating Center (NCC) Food and Nutrient Database.

/Methods: The NCC Database includes about 19,500 foods, and heme and non-heme iron values (mg/100g) were assigned to foods using a multi-step process: (1) Reviewed scientific literature and international food composition databases to gather analytical data; (2) Assigned values to the core foods based on the above sources and imputation rules; (3) For non-core foods, values were assigned using the NCC Food Calculation program; and (4) As a quality assurance measure, all assigned values were systematically reviewed for consistency across NCC food groups.

In the 2025 version of the NCC Database, heme and non-heme iron values were assigned to all foods, with no missing values. Core foods with zero total iron were assigned 0 mg for both forms of iron (14% of core foods). For eggs, dairy, and plant foods with iron content, 100% of the iron was assigned as non-heme (68% of core foods). For meats and seafoods, heme iron was calculated based on literature heme-to-total iron ratios, and non-heme iron was determined by subtraction of heme iron from total iron (18% of core foods). Imputation was required for 24% of the meat and seafood core foods.

The methodology used to add heme and non-heme iron to the NCC Database resulted in complete data, though imputation was required for some meats and seafoods.