Now, do you think they have specific data on this? Of course not. But they'll tell you it's a good idea anyway, and in fact tout it as a way to prevent heart disease. Wait for it though, because I found this, written for heart month, from the newspaper the Asheville Citizen-Times and I found it amusing in it's glorious contradiction:
"A key contributor to heart disease is lack of exercise — again, a factor that seems to affect busy women as they juggle jobs, kids, homes and community work and fail to make time for their own good health, Palmer said. And obesity is a critical factor, because “the more you weigh, the harder your heart has to work to give your body nutrients,” she said." [emphasis mine]
So, their first premise is that if you work your heart harder (by exercise) that you'll be healthier, but if your heart has to work harder because you're overweight or obese, that's bad. Can we say cognitive dissonance? Of course, being obese is associated with heart disease, but the primary reason for CHD isn't because your heart has to work harder, it's probably inflammation. However, I doubt having your heart work harder, either via strenuous exercise or by being obese, is very good for it.
I'm not saying that some activity isn't good, especially walking, but these people are advocating that an already busy person, who is not sitting at home watching television all day, should try to fit exercising into their already busy schedule. And that just creates more stress because they think it's a character flaw that they've gained weight and blame it on not getting to the gym. I think that makes about as much sense as telling a diabetic they should eat more fruit. Oh, wait. They do that too.
I tried to find some studies to either backup what they're saying or refute it, but it doesn't seem like any have really been done, at least with exercise alone. I would imagine to find out if exercise were beneficial, that you would take two very large groups of healthy men and women and have one group exercise and the other not. Then you'd find out if one group lived longer than the other. Most of the studies I've seen however, are in patients who already have CHD, are part of Statin drug trials, or part of a diet trial. There is no controlling for variables, they test multiple things at once, and that is not science. It's quackery is what it is.
There are multiple possibilities for why exercise could be beneficial, or not. One might be if carbohydrates cause heart disease by creating inflammation, and if you consume carbohydrates and exercise, you may burn off the carbohydrates before they can have an effect on your tissues, if you're a person who can burn them off. Most people who are obese have a problem metabolizing carbohydrates, so this probably wouldn't work for them. Or maybe if you never eat carbohydrates, you would have no need to exercise very much, and you would still live just as long as someone who ate carbohydrates and exercised. These are things that could be tested.
We should know so much more by now about what it is that is killing us, but we don't, and we won't. The food industry benefits from people eating their processed, expensive junk food and the pharmaceutical companies reap the benefits of people winding up on maintenance medication from such diets. To a lesser extent the fitness industry benefits from this too, as people try in vain to exercise to lose the weight they gain (exercise makes you hungry) by eating the "recommended diet". And the newspapers? They benefit by advertising dollars from the previous three industries to push what they want to be said.