How does having low iron affect my ability to lose weight?

Low iron means low energy, potentially leading to burning fewer calories and therefore forcing you to continue to lower your calorie intake to lose weight. That would be the primary way low iron effects fat/weight loss. Keep this in mind: take in fewer calories than you burn and you will always lose weight. That said, you don’t want to feel lethargic while doing it, so get your iron levels checked if you have reason to believe it may be low. And as long as you don't have a condition called hemochromatosis (an inherited disease that leads to iron-overload, affecting 0.5 percent of the population), we also recommend that your daily multivitamin and mineral formula contain a small amount of iron such as 5-10 mg depending on activity.