Patrick Holford has a problem with numbers. Sometimes, he cannot reproduce numbers accurately when they are laid out plainly, nor can he interpret them. However, there are times when his presentation of numbers is fishier than ever and this is causing some confusion. Some young readers have written to us.
Dear Holford Watch,
It was bad enough when we were being force-fed healthy-eating dogma during PSHE but now it is infesting our after-school clubs where we have to learn about nutrition with only brownie points on offer rather than the real thing.
We are tired of older people looking at us with crocodile tears in their eyes as they gloat that we will be the first generation to die before our parents. Then teachers set up projects where we have to review the research and data that assure us of our untimely deaths through toxic overload, pollution, Wi-Fi, too much food, too few nutrients etc. but certainly not a deficit of Prozac or Ritalin.
Last night we were advised to eat fish but to be careful because it contains toxins. We were told to look at a table of Omega-3 and mercury levels in different fish and to write a poem about how it made us feel. The table was quoted from a book by Patrick Holford so we were already a little suspicious. After all, Patrick Holford is the bowel-whisperer and doom-monger in residence for GMTV.
Chart of Omega-3 and mercury levels in fish: taken from pg. 101, New Optimum Nutrition for the Mind
|Fresh wild salmon
|Canned and smoked salmon
We couldn’t work out what the last column was supposed to tell us. The supervisor looked in the book but it didn’t say anything helpful. Then there was a fight because some people said that the numbers were wrong but when we asked the adults they did a nervous count on their fingers, giggled and changed the subject. Then they said that it is in a book that has been released in this new edition so it must be right.
Please help us.
Class 9, Erewhon School for the Jaded
Holford Watch is sympathetic to the plight of the young who are subjected to jeremiads about their health and bamboozled by adults who fail to understand the flaws in the basic science or maths of the ‘research’ that they thrust at them.
Dear Class 9,
We can understand why you are puzzled by the chart and we, too, find it annoying when we see a table without a legend to explain it. Before we address the errors in basic arithmetic, we recommend that you read Sandy at Junkfood Science who reassures us about the safety of fish despite the flip-flopping news headlines that are enough to frighten anyone into math hysteria.
There is no source given for the values that Holford quotes and some of his advice for fish consumption differs from that of the Food Standards Agency. Reading the text that precedes the chart, we learn that it:
lists fish in order of best to worst, in terms of the greatest amount of omega-3 with the lowest amount of mercury.
You were right to have misgivings about the numbers; what we have here is a failure to understand and convert units of measurement. The detail follows but we can only speculate that there are typos in the chart and errors in basic arithmetic.
The fresh wild salmon has 2.7 g/100g Omega-3, 0.05 mercury mg/kg but the 3rd column estimates that the ratio (or whatever that is supposed to be) is 54.0. Holford Watch reasons that the salmon has 27 g/kg of Omega-3 (or 27,000mg) which makes it a little easier to compare to the mercury. We estimate that Holford’s calculation is out by a factor of 10,000 but what’s a few orders of magnitude between guru and follower. We think that the number in the final column should be an unwieldy 540,000 rather than 54.
Ever ready to give Holford the benefit of the doubt, we ran some of the other calculations to determine whether there was (say) a consistent error in the units which would make some sort of sense. Sadly, there isn’t. E.g., Holford reports that marin has Omega-3 of 1.1 g/100g and mercury of 1.1 mg/kg and calculates the ratio as 1. We think that this should read 11g/kg (11,000mg) and 1.1 mg/kg with a ratio of 10,000 rather than 1. This is the same error of order of magnitude as for the fresh wild salmon. However, at a glance, it was obvious that there was a different order of magnitude error for the fresh mackerel: Holford reports around 10x more mercury, and a similar amount of Omega-3, yet the ratio is approximately the same, rather than differing by an order of magnitude (as it should). Fresh mackerel is reported to have 19.3 g/kg (19300mg) Omega-3 and 0.54 mg/kg of mercury: Holford calculates this as a ratio of 35.7. Holford Watch estimates that this should read 35,741: so, this is a lower order of magnitude than the other calculations.
Holford Watch is delighted that you spotted something fishy with the numbers as soon as you saw the table but we are a little dispirited that the adults who gave this to you didn’t spot the errors. It is irritating that these mistakes have obviously persisted despite the new edition of the book.
Did you write a poem about how you felt?
Pisces vobiscum – Holford Watch
Dear Holford Watch,
Our mothers always taught us that we should never be unkind
But they’ve never read New Optimum Nutrition for the Mind.
If Class 9 could have one retrospective, fervent, longed-for wish
It would be we’d never looked at Patrick Holford’s chart of fish.
Yours – Class 9