Do healthy people live longer?
Usually they do. There have been exceptions (heavy smokers living into their eighties and nineties), but healthy people tend to live longer.
I don't really care for analogies, but if you think of the human body like a plant, the plant usually needs sunlight and water to live. Without either, the plant won't live long.
If you eat junkfood, smoke, drink, sit around all day and eat lots of red meat, you probably won't live that long. The reason for this is your body will lose muscle (and since your heart is a muscle, the heart will stop working as efficiently as a healthy heart would), you will have clogged arteries, probably obesity, heart disease, and cancer.
Cancer cells feed off of sugar. Healthy people can eat sugar and junkfood, but they focus on whole plant foods to nourish the body and fight cancer cells.
There is also evidence that supports exercising is good for bone health. Without exercise, the chances of getting osteoporosis increases as we age.