The word diet has two meanings here in North America. The first 'diet' as in, "Some New Yorker's live on a tasty diet of knish's and hot dogs," is different than the, "I'm on the Atkins diet," meaning. The first denotes a lifestyle where, what you eat is incidental and largely determined by your environment. The second denotes a conscious decision to eat certain foods a certain times, in certain quantities.
Whatever the meaning a diet describes what you put in your body for fuel, and obviously the better the fuel the more efficient your body will be. And if your body is working at peak performance you'll have the power to undertake whatever you want. Exercise, adventure, happiness and romance will all come naturally if your body likes what you are feeding it.
So whether you are looking for a total lifestyle overhaul, or simply some hints on how to cut calories, lose weight and look smoking hot, there is a diet for you.