Hysteresis is a short term effect, measured in seconds. Full on magnetization won't happen to microscopic particles of iron at room temperature and atmospheric pressure in a tiny, rapidly changing, magnetic field.
And even if they became as magnetized as they possibly could, (which isn't very, because these are small particles) they're still going to be digested, reduced to single atoms, and bound to transferrin/ferritin/hemosiderin/hemoglobin proteins. Metallic iron doesn't naturally exist in the human body. The only people NMR imaging is contraindicated for are metalworks and such who are routinely exposed to high velocity metallic iron fragments, (via angle grinding, etc) that mechanically embed themselves in the skin, fingernail beds, eye orbits, etc. Completely unnoticeable in everyday life, less so when you climb inside a superconducting magnet.
Also, they're not shavings; they may be produced that way, but food-grade iron is milled down to a fairly fine mesh. It's a powder. There's no sharp edges.
Mild aside: Iron was so rare in the ancestral environment that humans never evolved a mechanism for excreting it, and it's heavily recycled. All ingested iron is metabolized, which means iron poisoning is fairly easy. This means that breakfast cereal, which is popular with children, who tend to have very low body weight, doesn't contain much of iron. The box of corn flakes I'm looking at only has 108 milligrams of iron in 340,000 milligrams of corn flakes.
Hysteresis is a short term effect, measured in seconds. Full on magnetization won't happen to microscopic particles of iron at room temperature and atmospheric pressure in a tiny, rapidly changing, magnetic field.
And even if they became as magnetized as they possibly could, (which isn't very, because these are small particles) they're still going to be digested, reduced to single atoms, and bound to transferrin/ferritin/hemosiderin/hemoglobin proteins. Metallic iron doesn't naturally exist in the human body. The only people NMR imaging is contraindicated for are metalworks and such who are routinely exposed to high velocity metallic iron fragments, (via angle grinding, etc) that mechanically embed themselves in the skin, fingernail beds, eye orbits, etc. Completely unnoticeable in everyday life, less so when you climb inside a superconducting magnet.
Also, they're not shavings; they may be produced that way, but food-grade iron is milled down to a fairly fine mesh. It's a powder. There's no sharp edges.
Mild aside: Iron was so rare in the ancestral environment that humans never evolved a mechanism for excreting it, and it's heavily recycled. All ingested iron is metabolized, which means iron poisoning is fairly easy. This means that breakfast cereal, which is popular with children, who tend to have very low body weight, doesn't contain much of iron. The box of corn flakes I'm looking at only has 108 milligrams of iron in 340,000 milligrams of corn flakes.