Combining iron-rich food with tomatoes in your diet may cancel out all the latter’s cancer-fighting benefits. A small study by a team of American and French scientists, published in the journal Molecular Nutrition & Food Research, found that the absorption of lycopene is significantly reduced when taken with iron-rich food. Lycopene are carotenoid that give tomatoes their rich red color. More importantly, lycopene are antioxidants that help us fight against cell damage and cancer. 
The team measured the absorption of lycopene in the upper gastrointestinal tract in the absence and presence of iron. For this purpose, 7 males were provided tomato-based meals with and without ferrous sulphate, a common iron supplement for people with iron deficiency. The team then analyzed their blood and digestive fluids.
Lycopene levels were significantly lower when the participants took their meals with iron supplements. The level of lycopene dropped further with time, becoming negligible. This indicated that when iron is present with tomato, the latter’s lycopene absorption by the human body becomes insignificant.