David Friedman on Salt and Fish Oil
There is a longstanding argument for reducing the amount of salt modern Americans consume, based on evidence that a high salt diet tends to produce high blood pressure. A recent European statistical study, however, reported just the opposite of what that argument suggests — evidence that lower salt intake was correlated with an increased risk of death from heart disease. Similarly, there is evidence that an increased consumption of omega 3 oils reduces the risk of heart attacks. But it has recently been reported that it also increases the risk of the more serious form of prostate cancer.
Friedman argues that we shouldn’t be surprised by these results. We are the product of evolution that has optimized us for our environment and in any optimization equilibrium a change that improves along one dimension is likely to produce a worsening in other dimensions. He then writes:
The fact that some change produces a gain in one measurable dimension that matters to us is very poor evidence that it produces an overall gain. Before altering behavior or diet, one ought to look for evidence of net effects on life expectancy or other reasonably final goals, not merely for desirable effects on one input thereto.
Friedman makes an interesting argument, for which there are plenty of examples. Reducing early adult mortality from all causes has resulted in higher incidence of cancer later in life. Making food cheap has reduced mortality from malnutrition and increased population stature over time. But it has also increased obesity and diabetes over time in populations that (historically) had to scavenge for food in a hostile landscape.
Interesting spin. And probably correct.
Friedman is assuming that our evolutionary make up is optimal. He may be right.