When your iron levels falls too low, that's when energy drops off the radar as well. Therefore, in order to improve this scenario, you either have to consume more iron rich foods; or the simpler solution; supplement with iron instead.
In addition, since women generally do not consume large volumes of red meat through their diet and what is consumed is often the first to go on a fat loss plan; this means they fall even lower in iron intake yet.
Vegetarians will also benefit quite a bit from using an iron supplement since they also tend to reduce the amount of iron-rich foods they're consuming in their daily diet.
If these are usually in your diet, then you can use a slightly lower dose of iron supplementation, but if you aren't including these foods all that often, make sure you take the maximum dose of iron at approximately 10 mg per day for males and 15 mg per day for females.
It's also important to keep in mind that iron taken in through supplementation (heme-iron) is absorbed better by the body than iron that's consumed through vegetable sources.*