The 'science' of living a healthy life?

Yesterday's NYT Magazine was devoted to The Science of Living a Healthy Life. Does exercise help us lose weight? Is estrogen replacement good or bad? Is marriage good for your health? We could stop right here by saying that the answer to living a healthy life is easy, and there's no need for expensive studies because we've known for millennia how to do it -- moderation in everything. But, this advice doesn't fill careers -- or magazines.

So, science boldly marches on. But how could we possibly not know the answers to these questions, after billions of dollars, thousands of state-of-the-art studies, and the devotion of many smart minds to the problem? In short, it's because the questions are wrongly posed. They address a causative factor as though it can be studied out of context -- as though you could simply add exercise to your life and measure what happens as a direct result. It exemplifies the way we've earlier described how science 'tunnels' through complex truths to try to get at isolated subtruths, when what is needed is the greater truth.

Indeed, weight loss is a 'simple' equation whereby expending more calories than you take in must result in shedding pounds, because that energy must be derived from stored form in tissues. We only get that energy from food. Simple beyond simple?

No, not really. Expending calories triggers other effects, hormonal and otherwise, that cause you to want to consume more calories than you would if you hadn't exercised, so simply adding a workout to your daily schedule is unlikely to result in weight loss. Eating less and exercising is another story, however. But, eating less without exercise results in weight loss as well (because of that simple energy balance equation, and the fact that just living and breathing require energy). But either way, once the weight is lost, it's very easy to put it right back on -- at least in our culture, with its temptations and so on. Here's where exercise might actually help -- it turns out that to maintain weight loss, exercise might be the key, though it's not clear why.

So, the answer to whether exercise causes weight loss is that it might do so if only it didn't trigger those other effects. Especially in women, apparently, as though women have evolved a mechanism to maintain body fat. The Just-So explanation for this would be that extra body fat is important for successful reproduction (gestation and lactation). But, this assumes that our species evolved in conditions in which there were excess calories to store. An unlikely scenario. So for now, it's possible that women's hormone repertoire handles body fat differently from men's, but it's not yet clear whether that is actually so. And since men have to be the tough guys defending the home front, and out hunting dinner, why shouldn't they, too, have comparable levels of the hunger effects?

As to whether marriage makes people healthier, as one of the stories in this week's magazine says, well, it depends. Again, it's impossible to answer this question out of context. And, does estrogen replacement improve the health of menopausal women? The answer again is, it depends. These questions assume a linear, simple, cause-effect relationship that just isn't the way biology works. We know this from genetics, epidemiology, psychology, economics, and so on. Now kinesiology and physiology are confirming this, in their inability to tell us how to live a healthy life. They raise the question as to why we have kinesiology departments and big grants if even these things haven't been worked out.

But from a more sympathetic view, the continued inclarity on these very basic kinds of questions shows that prevailing scientific methods just aren't yet up to measuring cause and effect in complex systems of this sort.