If something is in excess that doesn’t mean it is good for us! Lets talk about iron absorption with red meat compared to plant foods. Funny how people think just because something is more absorbable it should therefore be better for us. Heme iron and non-heme iron. There is a big difference. Heme iron is obviously from dead flesh (blood) and non heme from plant foods!
Because the human body has no mechanism to rid itself of excess iron we have evolved to regulate this. Iron is absorbed through our intestines and if iron stores get too low the intestines know when to boost the absorption, if iron stores are too high then the intestines block the absorption to maintain us in the sweet spot! This also only works with the primary source of iron in the human diet from plant foods (non-heme).
Heme iron from dead flesh however cannot be regulated by the body and therefore absorbs straight through the intestinal wall even if there is excess iron in the body. This is when the body gets into an iron overload and creates all sorts of problems and sets the body up with a higher risk of dis-ease.
So the body has no control over iron absorption when eating animal flesh. This is why Vegetarians and Vegans tend to be lower in iron when it comes to blood tests because the 'normal' range is elevated due to all those people eating flesh which in turn boosts there level of iron in the body without knowing it is much more harmful for them.
In terms of how much the body can absorb we believe that it is very hard to get an exact number from the foods we eat because you can't really say that this plant food has this much iron in it so my body will absorb all of it. Iron absorption also depends on how many other nutrients that plant food has because all of the nutrients from that plant food work together to get absorbed. If you eat a variety of WHOLE foods (Fruits, Vegetables, Whole Grains and Legumes) you will get the exact amount of iron the body needs so that you can be in that sweet spot :)