This is the only big study on breastmilk and iron, and came to the conclusion that extra iron not necessary (for healthy full-term babies) before 6 months:
K.G. Dewey, et al., Iron supplementation affects growth and morbidity of breast-fed infants: results of a randomized trial in Sweden and Honduras
Journal of Nutrition 132, no. 2 (Nov 2002): 3249-55.
Contents: 4-6 month old infants on breastmilk but allowed tastes of vegetables, control group supplemented with iron, result: extra iron un-necessary.
And the gluten stuff is rubbish. It is based on something that happened in Sweden in the late 80s or early 90s, I think. Doctors wanted to try to induce gluten intolerance/allergies as early as possible, so a decision was made to trial really increasing the amount of gluten in välling (a sort of gruel, consisting mainly of wheat and milk which babies in Sweden are fed in bottles instead of follow-on formula, often for several years), and baby porridge. At the same time, but not connected, the recs for intro of solids changed to 6 months (or possibly 4-6 months?), from 4 months. The result were massive, as many more children developed gluten allergies/intolerances. Around the same time they decreased the gluten in these things, the rec for food intro went back too. Unrelated. And research has been done since, and the major rec for gluten intro is based on this: Introduce gluten as late
as possible, as slowly
as possible and, most importantly, under the protection of breastfeeding
. In Sweden, most breastfeeding mothers stop breastfeeding between 6 and 8 months. Thus the far to common advice to introduce gluten at 4-6 months, or 6-8 months, to "prevent gluten intolerance" or "prevent allergies".
I'll see if I can find links to studies and stuff for this.