Flip a bag of raisins over and the nutrition panel gives you a number you want to believe: 1.88 milligrams of iron per hundred grams. Roughly ten percent of your daily value, printed in a font designed to look like fact. Your body reads that number differently.
Between what a food contains and what your body absorbs sits a gap most nutrition labels never mention. For raisins, that gap is enormous.
Are Raisins a Good Source of Iron?
Raisins contain iron on the label, but the body absorbs very little of it. A USDA and Cornell study tested all three common raisin types using the standard cell model for iron absorption, and every variety showed low bioavailability. High concentrations of tannin inhibitors — concentrated during the drying process — trap the iron before it reaches your bloodstream.
— Yeung et al. 2003 · Journal of Food Science · n=3 varieties
USDA and Cornell University food scientists put all three common raisin types — golden, dipped, and sun-dried Thompson — through a cell-based test that mimics human iron absorption. Every variety came back the same: low iron bioavailability, across the board. Not borderline. Not one-variety-saves-it. All three failed.
The printed milligrams exist. They sit inside the raisin. They just never reach your bloodstream in meaningful amounts.
What blocks them is the same thing that makes a raisin a raisin. Drying a grape concentrates everything — the sugars, the iron, and the tannins. Those tannins are polyphenol compounds that bind to non-heme iron the way a lock grabs a key, except the lock never opens. The same drying process that raises the iron number on the label also concentrates the compound that traps it.
WHAT THE LABEL MEASURES
1.88 mg iron per 100 g — roughly 10% of your daily value
WHAT YOUR BODY ABSORBS
Low bioavailability — tannin inhibitors trap the iron before it reaches your bloodstream
Absorption inhibitors showed up in concentrations high enough to raise a harder question: raisin tannins may reduce iron absorption from other foods eaten in the same meal. Your morning oatmeal with raisins might not just miss the raisin iron — the raisins could be pulling iron away from the oatmeal too.
That cross-meal effect is an inference the researchers drew from the inhibitor levels they measured, not something they tested directly with co-consumed foods. The absorption test itself used a cell model rather than human volunteers — a validated method, but one that cannot capture everything a stomach does. The finding is clear enough to rethink the raisin-for-iron habit. It is not complete enough to panic about every raisin in your trail mix.
What raisins highlight is a question worth asking about every food that claims to deliver a mineral: can your body actually get to it? Spinach raises the same question with oxalates, and onion and garlic offer a surprisingly practical answer. If you want a meal where the iron actually arrives, a lentil coleslaw built around that exact problem pairs high-iron ingredients with raw cabbage — sixty-two milligrams of vitamin C working as the rescue mechanism the raisins cannot provide.
