Eating lots of green salads is absolutely good for you. Leafy greens of all varieties should be a big part of what you eat every day. But don’t put commercial salad dressing on that salad. The number one ingredient in almost all commercial dressings is either canola oil, soybean oil or vegetable oil. All are man-made industrial oils that should not be part of anyone’s diet.
The vegetable oil industry has done a great marketing job convincing us that canola oil and other vegetable oils are “heart healthy”. But in fact, they are not. They are toxic. You should be doing everything you can to eliminate them from your diet.
Keep your dressings simple: Extra virgin olive oil with some balsamic vinegar makes a great dressing.
Also note that just about every restaurant you go to will be using vegetable oils in their dressings, not olive oil. Be sure to ask.
If you want more detail, here’s a (somewhat) brief article on soybean oil: http://drcate.com/study-soy-oil-promotes-obesity-and-liver-damage/