When Canadian science graduate Christopher Charles visited Cambodia six years ago he discovered that anaemia was a huge public health problem.
In the villages of Kandal province, instead of bright, bouncing children, Dr Charles found many were small and weak with slow mental development.
Women were suffering from tiredness and headaches, and were unable to work.
Pregnant women faced serious health complications before and after childbirth, such as haemorrhaging.
Ever since, Dr Charles has been obsessed with iron.
Anaemia is the most common nutritional problem in the world, mainly affecting women of child-bearing age, teenagers and young children.
In developing countries, such as Cambodia, the condition is particularly widespread with almost 50% of women and children suffering from the condition, which is mainly caused by iron deficiency.
The standard solution - iron supplements or tablets to increase iron intake - isn't working.
The tablets are neither affordable nor widely available, and because of the side-effects people don't like taking them.
Dr Charles had a novel idea. Inspired by previous research which showed that cooking in cast iron pots increased the iron content of food, he decided to put a lump of iron into the cooking pot, made from melted-down metal.
His invention, shaped like a fish, which is a symbol of luck in Cambodian culture, was designed to release iron at the right concentration to provide the nutrients that so many women and children in the country were lacking.
The recipe is simple, Dr Charles says.
"Boil up water or soup with the iron fish for at least 10 minutes.
"That enhances the iron which leaches from it.
"You can then take it out. Now add a little lemon juice which is important for the absorption of the iron."
If the iron fish is used every day in the correct way, Dr Charles says it should provide 75% of an adult's daily recommended intake of iron - and even more of a child's.
Trials on several hundred villagers in one province in Cambodia showed that nearly half of those who took part were no longer anaemic after 12 months.