The Iron Stable Isotope Fingerprint of the Human Diet

Abstract

The stable isotopes of iron disclose the metabolic pathways of iron within the human food chain. We have measured with precise multicollector ICP-MS the iron concentrations and stable isotope composition of 60 food products that are representative of the average German diet. We find that vegetable falls within the range typical of strategy I plants (-0.1 ‰ to -1.4 ‰ in δ 56 Fe), crop products and processed crop food into the range typical of strategy II plants (-0.6 ‰ to +0.4 ‰), and animal products into the 54 Fe-enriched range known for animal tissue and blood (-1.1 ‰ to -2.7 ‰). Weighting these isotope compositions by the average iron dietary sources, we find a representative composition of European vegetarian diet of -0.45 ‰, while that of omnivores is -0.82 ‰. For human blood, known to be enriched in light iron isotopes, we find a fractionation factor for iron absorption of -2.0 ‰ to -2.3 ‰ for vegetarians (female and male, respectively), and -1.3 ‰ to -1.5 ‰ for omnivores (female and male, respectively). Knowing these fractionation factors is a prerequisite for using stable iron isotope ratios in blood as monitors of intestinal iron uptake regulation.

Potential of non-traditional isotope studies for bioarchaeology

“…The existence of a trophic level effect has been demonstrated for most of the non-traditional isotopic systems studied so far: Ca (Clementz et al 2003 Jaouen et al 2013b;von Blanckenburg et al 2013). For Ca, this pattern is not systematically observed (Melin et al 2014).…”

“…Similarly, von Blanckenburg et al (2013) have shown that vegetarian diets are associated with a Fe isotopic fractionation factor 1.5 times higher than that of omnivore diets, but in this case, the light isotopes are preferentially absorbed. Because the Fe isotope composition of vegetarians' diet is generally much higher than that of omnivores, the blood isotope compositions of these two groups are similar and cannot be distinguished (Van Heghe et al 2012;von Blanckenburg et al 2013). It should be noted that ovo-lacto-vegetarian and omnivore diets both mix animal and plant products.…”

δ56Fe in seabird guano reveals extensive recycling of iron in the Southern Ocean ecosystem

“…Iron isotope fractionation may also occur during physiological processing of iron by animals. Here, evidence for distinct isotopic signatures of animal‐based dietary elements in human diet suggest that iron may become progressively deplete in the heavy isotope 56 Fe with trophic transfer within food webs (e.g., Von Blanckenburg et al ).…”

“…In the case of isotopic signatures of iron, d 56 Fe, known pathways for isotope fractionation by bacteria offer a mechanism for identifying biologically recycled iron from that newly made available from lithogenic sources such as weathered rock or dust (Beard et al 1999;Brantley et al 2001;Waeles et al 2007). Additionally, indications that iron isotopes can be fractionated within food webs highlights their usefulness as proxies for biological uptake and recycling of iron (Von Blanckenburg et al 2013). Recent advances using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) allow for isotopic discrimination of lithogenic (Waeles et al 2007) and biological Fe pools (Beard et al 1999) in the marine environment, including seawater (Conway et al 2013;Conway and John 2014).…”

Elemental and Isotopic Mass Spectrometry

“…Knowing these fractionation factors is a prerequisite for using stable iron isotope ratios in blood as monitors of intestinal iron uptake regulation [221]. For example, a recent publication investigates the iron stable isotope fingerprint of the human diet.…”