There's a study being done by French researchers, "Drinkers Exercise Most", and it touches on something I've come to realize regarding the irony with gyms.
Before I continue let me first say that I too was at one time a "gym rat", a slave to all those machines and exercise equipment many of which closely resembling some sort of medieval torture device. This was during a time in my life when I thought I was healthy although my diet consisted of mostly processed foods; a time when I thought I was in great shape although I was riddled with tendinitis in most of my joints; a time when I thought this 5-6 times a week addiction (to the gym) was good for my body despite all the crap (whatever latest and greatest the GNC had to offer) that I was taking.
I feel I can speak the truth on this subject, as painful it may be for all the gym rats to hear, because I too was once an addict. The gym by definition is supposed to signify or at least indirectly equate to a healthy lifestyle, yet most of those who go (at least in my experience) live unhealthy life styles.
Most gym goers fit into one of four categories; the "young and naive" usually doing at least half of the exercises incorrectly and are all too easily influenced by the next group... the "muscle heads", usually taking a colorful assortment of daily muscle growth enhancers some legal and some not and concerned only about size. Then there's the "cardio freaks", those who seem to be going full speed from the moment they get in moving only from on one piece of cardio equipment to the next. Finally there is the "rehab/seasonal group" consisting of both young and old either rehabilitating an injury or trying to look good in a bathing suit, and both usually assisted by the "trainer" on staff.
The problem is most of these people (some more blatantly obvious than others) do not practice the "healthy lifestyle" outside the gym. They either eat poor unhealthy diets and or drink too much, they smoke, they consume way too many drugs (be it pain killers, Rx's, or anything from the GNC), they subject themselves to toxins on a daily basis, and they usually do not know what it truly means to be healthy... I know I didn't.
Fact... the 2 biggest membership periods at a gym are between New Years (the "resolution") and the Super Bowl when most people finally give in to that glutinous temptation, and that "end of winter/beginning of spring" period that ends as soon as the summer beach days begin. That alone proves that the gym drives a temporary urge in many people to "get fit quick", but just as those fad diets drive that "get thin quick" urge they usually falls short of any positive results and seldom result in a healthier lifestyle.
There is no substitute for a healthy diet, period. If you can honestly say that you eat health, and by that I mean a diet consisting of mainly fresh organic whole foods, then and only then should you even consider a "gym" as your method of staying fit.