The Bioavailability of Iron from Meat, Spinach, Soy Protein Isolate, Meat:Spinach and Meat:SPI Mixtures Fed to Anemic and Healthy Rats

Two Experiments were conducted to investigate the effect of iron status and iron source on iron bioavailability using the rat model. Beef was proportionally mixed with spinach (Experiment I) or soy protein isolate (Experiment II) to test if meat enhances the absorption of iron from spinach or SPI. Five diets with the iron from meat:spinach (or SPI) ratios of 100:0, 75:25, 50:50, 25:75 and 0:100 were prepared and fed to rats. FeS04 was used as a reference. Two trials of rats were used in Experiment I. In trial I, half of the rats were made severely iron deficient (Hb 6.3 g/dl) and the other half mildly iron deficient (Hb 8.8 g/dl). In trial II, half of the rats were depleted to severe iron deficiency and the remainder were not depleted (Hb 11.3 g/dl). Hemoglobin regeneration efficiency (HRE), apparent absorption and 59Fe absorption were compared. The HREs were 41, 53 and 36% (spinach); 42, 51, and 44% (beef) and 73, 66 and 46% (FeS04) in severely, mildly iron-depleted and healthy rats and 56 and 42% (SPI) in iron-depleted and healthy rats, respectively. Iron depletion stimulated iron absorption. This effect was very significant for rats fed a FeS04 supplemented diet and lessened for rats fed diets containing beef, spinach or SPI as the iron source. Spinach and soy protein isolate were good iron sources both having similar iron bioavailabilities as beef. Beef ~as a good iron source, as noted in other reports; however, enhancement of meat on absorption of iron from spinach and SPI did not occur. Hemoglobin regeneration efficiency is a simple, accurate and definitive method for measuring effects of iron source and iron status on iron bioavailability. Apparent absorption gives similar values to HRE. However, it requires meticulous iron analysis and has more potential for errors. Extrinsic radioisotope tagging is an easy method, but there is evidence of possible incomplete exchange of radio tracer with iron in food. The different absorption pattern between FeS04 and food iron suggests a third iron pool, highly soluble iron salt, in addition to heme and nonheme iron complex pools