Does whole grain product decrease absorbtion of iron and if yes how it is healthy as it may cause iron deficiency anemia

No: This isn't a realistic fear. You're a young man. If you have any reason to believe your are iron deficient, and you are not on an ill-advised iron-poor diet / are not a non-supplementing vegetarian, you need to find the cause -- at your age, it's a bleeding ulcer or worse until proved otherwise. If you're asking because you like whole-grain bread -- good for you. Enjoy.

Phytates in grains: Whole grains, legumes, nuts and seeds contain antioxidant compounds called "phytates." unlike other animals, we humans have no phytase to degrade these -- & they can bind to minerals like iron instead. If your diet is exclusively grains, iron deficiency could result. If your diet also includes veggies, leafy greens, vit c (increases iron absorption) foods, and meats with heme iron, you're fine.