Does anyone know (or have references/resources to) how much calcium actually inhibits iron absorption?
Example: Let’s say I make a protein shake with 40% RDI iron and toss in a cup of animal/plant milk with 30% RDI calcium. Then let’s compare it to doing 50/50 milk and water. How much iron are we actually getting in each scenario?
Iron absorption is inhibited because 2+ ions have non-specific absorption sites in the intestines. The body typically only absorbs 10% of ingested iron, less if it’s non-heme iron (plant based iron). Non-heme iron is ingested as Fe 3+ and isn’t as readily absorbed as Fe 2+. An acidic environment does help reduce Fe 3+ to Fe 2+, but dietary calcium will not affect stomach pH unless it’s calcium carbonate.
Meat, fish, poultry are the ideal sources of iron because your body will absorb the heme iron better than non-heme
Calcium increases the pH of your stomach. Iron requires a low pH for absorbance (hence why you should take it with vitamin C pills and not within 2 hours of an acid blocker like Protonix or Pepcid). So the decrease in iron absorbance will be proportional to the alkaline portion of your smoothie. You can get around this by adding more acidic fruits to protein shakes or smoothies to have a lower total pH of your drink then the calcium content will not matter as much.