Too much of ANYTHING can be converted to fat. If you ingest too many calories, you will gain fat. Doesn't matter then source...it's just that it is MUCH easier to eat too many fat/carb calories.
Not sure of your goals, your history, your stats, your food choices....etc. More information is helpful. What kind of diet are you trying to do?
As a VERY general statement, most people do well with a high protein, moderate carb and moderate fat diet. But others respond better to other diets. Yo uhave to find what works for YOU. It is a trial and error process, one that can take years to figure out completely.
But in the short term, keep your protein from lean meat sources such as lea nred meat, chicken, turkey. Carbs should be CLEAN and basic...NO PROCESSED FOODS.... potato, oatmeal, brown rice, green veggies. Fats are healthy...Olive Oil, Flaxseed Oil, almonds, Natty PB. Fish is another good protein/healthy fat source.
Post up more info and people can give better advice.