Are diet foods harmful?

Not like that , only few diet are harmful , harmful means they causes some side effects like food poisoning or some health related problems .
For examples : Aspartame is a sugar substitutes , high intake may causes memory problems in the olders & pregnant women. Aerated drinks are aslo called fizzy drinks, it has unhealthy salt ,aspaartame, chemical preservatives & unhealthy colors. This may causes overweight , unbalanced insulin & blood sugar level in the blood . Some others eamples like cholesterol free foods(unhealthy), sweet clear water like diet drinks which contains small qty of aspartame.

Hi

I agree with poonam. Some more example for unhealthy diet like high intake of non- veg leads many health problems like heart disease , some times kidney problem because of high content protein in non-veg. Regular use of canned foods may leads some health problems like food poisoning, etc.

In addition, don't have packed soups, and ready to made food items. They are high in preservatives and fats. avoid having them often, as they cause unnecessary water retention and weight gain.