[cbhl]

True, but if you're eating raw spinach you need something like nine cups to get your RDA (assuming RDA of 8mg/day, and about 3 cups per 100g). Females 19-50 are told to eat 2x that; pregnant females 3x (27mg/day(!), source: https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/).

If you cook it, then your 300g spinach reduces to something like one and a half cups, but you have to be careful to not lose water-soluble iron to your cooking method. Also, you have to like the texture of wilted spinach.

If you're used to eating half-cup sides of spinach, making spinach your primary iron source is a fairly major change to how you eat.