SummaryThe study of the total content of essential minerals in food is important; however, only these values do not provide truly accurate information regarding their nutritional value. Bioaccessibility and bioavailability are key concepts that provide us with more precise information about these values. This study focuses on quantifying calcium, iron, magnesium and zinc in adult supplementation samples, specifically fortified dairy products (FDP) and modified enteral and oral nutrition formulas (EONF) for adults. The samples used in this work were digested using nitric acid and oxygen peroxide to quantify the total contents of Ca, Fe, Mg and Zn. The effectiveness of the acid decomposition procedure was evaluated through an accuracy test using the NIST 1547 certified sample, which exhibited recovery percentages of 97% for Ca, 95% for Fe, 101% for Mg and 90% for Zn. To assess bioaccessibility, extraction procedures were conducted using the in vitro Simple Bioaccessibility Extraction Test (SBET). The bioaccessibility ranges, expressed as percentages, were 14%–62% for Ca, 23%–65% for Fe, 21%–46% for Mg and 33%–64% for Zn. Based on the results, it can be concluded that evaluating bioaccessibility is important for assessing the nutritional content of adult supplementation, as the labelled contents are not always accessible to the body.