Cooking methods alter the composition of the nutritional values in food.
It is best to avoid boiling broccoli. A far better way is to steam, as the veg cooks, but doesn’t release nearly as much nutrients in the process. With boiling, water soluble vitamins such as Vitamin C and B leak out, which does not happen as much through steaming. The reason is because most of the vegetable’s brilliant nutrients are lost in the bubbling water.
Various vegetables are best cooked in different ways. Different flavours come about through different methods.