This blog post is not too concerned with the accuracy of the guidelines per se; it is more concerned with the existence of guidelines in the first place. Whilst we may be able to accurately test the relationship between lifestyle factors (such as diet) and health outcomes – and the array of differing results suggests that this is certainly not a simple relationship – it is impossible to scientifically produce a guideline for everyone, and meaningless to judge people’s behaviour by how strictly they adhere to the guidelines.
Take a trivial example. Televisions come in all shapes and sizes, and generally a larger television costs more money. There are experts who give their opinion on which television to buy, perhaps weighing up the cost of an extra couple of inches of screen size against the benefits of having a larger screen. Imagine they come up with a recommendation that people should not buy a television bigger than 32 inches – this is the point where they recommend that the extra inches are not worth the extra cost. I doubt we would ever analyse surveys, and doubt even more if 45% of adults in the UK were exceeding these guidelines.
So why do we do so with diet, exercise, or alcohol? Of course, all of these behaviours have a health implication – a health implication which means increased cost to the NHS – but the guidelines around these are no more scientific than the television example. There is no scientific reason why the government recommends that women do not drink more than 3 units a day - although the guideline suggests that they have weighed up the costs and the benefits, it is unlikely that they actually have. Though they may be able to estimate the cost, the benefits are much harder to measure.
What we need instead is to be informed of the associated risks for lifestyle choices. It is not particularly useful to know the recommended level of consumption, any more than it is to know which television size is recommended. What we would want to know – and do know with televisions – is how much an extra couple of inches of screen size costs. We can then weigh this up against our own perceived benefits. For health-related lifestyle behaviours, then, we need to know the marginal relationship between consumption and harm to make an informed decision about the optimal level of consumption.