Lets face it, the American diet is terrible. It is full of cholesterol and bad fats and empty calories. I am not too familiar with the diets of other parts of the world, but chances are unless you are really watching your diet, you are probably not getting all the nutrients and vitamins you need.
I understand it is hard to get in 5 servings of vegetables a day, but with a serving of Greens +, you get exactly that. It is very easy to mix, and can go great with homemade shakes. Greens + is the most highly regarded greens supplement, and is used by professionals and amateurs alike. The downside is that is is a bit expensive for a constant supply. There are reports of nearly identical generic brands at places like Whole Foods and Trader Joes.