RDA, EAR, AI and BOLLOX

Back to to obesity and blah blah blah. Our local news popped up with a report that had me interrupting the reporter; statements such as ' perhaps the government could tax unhealthy food? [Okay define 'unhealthy'] or foods that were high in fat or contained too much salt? [okay define 'high' and 'too much']'

GMTV appeared with a simple salt warning 'too much salt leads to strokes and' blah blah blah, except of course too little salt also leads to strokes etc. Hmm hey that didn't get mentioned now did it.

Anyway back to that whole 'unhealthy', or 'too much' argument; how to work it out? Easy, we have an Recommended Daily Allowance (RDA) for salt it's 6g, so we can set some arbitrary point whereby if one portion exceeds that point it's deemed 'high'. Of course we don't really have an RDA for salt - surprise. We have an RDA for sodium, which is a component of salt (sodium chloride), and that's 1.6g . So multiply that by 2.55 to get the salt limit and we get 4.08g um that's not 6g.

Alright forget that how do we get an RDA anyway. Well that's easy too we take the Estimated Average Requirement (EAR) for each substance... Okay the EAR is the intake that meets the estimated need of 50% of that group (so you can sort by sex and age). If you just used the EAR that would mean 50% of the group would not be getting enough nutrients, so the RDA takes that figure and adds some, usually about 20%. Why 20%? Um well, um because um; look science!

[Update - Anonymous comment says my 20% is arbitary and the RDA is in fact "set at two standard deviations higher than the EAR" which is simply a more scientific guess]

The EAR is scientifically tested, in one study of Taiwanese children levels of B6 were monitored. The doctors took the standard fluids and measured height and body fat etc. Their growth matched that taken from a previous study and so was deemed normal and healthy, so there levels of B6 were 'good'. So their health was determined to be normal/good because they matched the patterns of a previous group whose health was determined to be normal/good - turtles all the way down here.

Sadly some nutrients don't have an EAR so they get an Average Adequate Intake (AI) instead, the AI is calculated from various means. If someone turns up with some disease and a low X factor (or a high X factor) compared to a non-diseased person then you can say need more (or less) of that X factor. Or you can just see what people normally intake and judge whether they're healthy or not. Say doesn't that last one sound like the EAR tests?

In essence it appears that the RDA is a fudged factor of EAR or AI that has been determined by qualifying a group of people as 'normal/healthy' and measuring their intake. Of course it takes zero account of your lifestyle, do you exercise a lot, build up a sweat? Hey you're loosing salt you now need the RDA plus what you've lost which is um don't know.

So people who exercise need to replace those lost nutrients, which means eating/drinking foods that will be deemed 'high' in said nutrients, which some people want to tax. Yeah tax those damn sweaty joggers and gym users serves them right.