One of the key factors relating to risk of death from coronavirus is how much you weigh. The overweight have a higher risk of dying if symptoms are severe, the obese even more so, likely because lung capacity is not proportional to body size. Of all the members of the government infected in the early stages of the outbreak, it's perhaps no surprise that the Prime Minister was the only one to end up in intensive care.
Boris Johnson is 5 foot 9 tall and supposedly weighed 17½ stone when he was taken to hospital. We can use the NHS BMI healthy weight calculator to see that this translates to a Body Mass Index of 36.2. The arrow here is deceptive because 36.2 is way off the end of the scale.
I'm roughly the same age and height as the Prime Minister but weigh five stone less. Today's post is about why I'm not sure if I'm overweight or not.
BMI is a simplistic calculation, one-formula-fits-all, which takes no account of age, gender or muscle mass. It's calculated by taking your weight (in kg) and dividing it by your height (in m), then dividing by your height again.
Boris Johnson weighed 111kg and is 1.75m tall.
His BMI was 111 ÷ 1.75² = 111 ÷ 1.75 ÷ 1.75 = 36.2
And 36.2 means the Prime Minister is obese.
My problem is that I know how much I weigh but I'm not 100% certain what height I am.
I think my height is 5 foot 10. This would be good news, because my BMI comes out as a healthy weight.
But I've also been measured as 5 foot 9. This would be bad news, because in that case I'm overweight.
One height gives me a BMI of 24.4 and the other 25.3. It's only an inch of difference but it kicks me into a whole new weight category. Coronavirus doesn't care, it'd have the same effect on my body no matter what, but I'd feel marginally more reassured if I wasn't officially overweight.
I'd also feel a bit smug, because England's obesity figures are shocking.
For adults over 45 years of age, about one-third are obese, 40% are overweight and only a quarter have a healthy weight. Men are more likely than women to be overweight or obese. Women are more likely than men to be obese. In my age group, only 20% of men have a healthy weight. If I was one of them I'd be rightly pleased.
I'd be particularly pleased because, contrary to expectations, I've actually lost weight under lockdown.
I weigh myself daily so I know that throughout the first eleven weeks of this year I weighed 12 stone 11, give or take a pound.
5 foot 9(1.75m) 12 stone 11(81.2kg)
5 foot 10(1.78m) 12 stone 11(81.2kg)
81.2 ÷ 1.75² = 26.5
overweight
81.2 ÷ 1.78² = 25.6
overweight
Whether I'm 5 foot 9 or 5 foot 10, I was definitely overweight.
Then in the week beginning 16th March my weight dropped abruptly to 12 stone 7. It can't have been activity related because I was walking less as lockdown approached. Instead I put this down to a change in diet, specifically a sudden adjustment to my eating habits in the face of potential food shortages. Eat less, weigh less.
5 foot 9(1.75m) 12 stone 7(79.4kg)
5 foot 10(1.78m) 12 stone 7(79.4kg)
79.4 ÷ 1.75² = 25.9
overweight
79.4 ÷ 1.78² = 25.1
overweight
But I was still overweight, technically, marginally, even if my height was the higher of the two possibilities. The rules are brutal. Anything over 25 is overweight, and 25.1 still tipped me over.
I stayed at 12 stone 7, give or take a pound, for a month. Then in the week beginning 20th April my weight dropped abruptly to 12 stone 4, give or take a pound, where it's remained ever since. I have no idea what's caused this step change, but I'm not complaining because it's brought good news.
5 foot 9(1.75m) 12 stone 4(78.0kg)
5 foot 10(1.78m) 12 stone 4(78.0kg)
78.0 ÷ 1.75² = 25.4
overweight
78.0 ÷ 1.78² = 24.6
healthy weight
If I'm 5 foot 9 then I'm still overweight, but if I'm 5 foot 10 then I'm a healthy weight. I hope it's the latter, because I haven't been a healthy weight in years.
Given that the BMI statistic is a continuous function, it can actually be calculated for any fractional value. So, seeing as I'm not sure precisely what height I am, it might make more sense to assume I'm 5 foot 9½.
5 foot 9 12 stone 4
5 foot 9¼ 12 stone 4
5 foot 9½ 12 stone 4
5 foot 9¾ 12 stone 4
5 foot 10 12 stone 4
25.4
overweight
25.2
overweight
25.04
overweight
24.9
healthy
24.6
healthy
Damn, even at 5 foot 9½ I'd still be overweight. It's utterly marginal, but this is a cruel classification and even a tiny decimal counts. Were I instead 5 foot 9¾, however, that'd be fine.
I can also take things one step further and consider a range of weights as well as heights.
5 foot 9
5 foot 9¼
5 foot 9½
5 foot 9¾
5 foot 10
12 stone 7
25.8
25.7
25.5
25.3
25.11
12 stone 6
25.7
25.5
25.3
25.1
24.97
12 stone 5
25.5
25.4
25.1
25.001
24.8
12 stone 4
25.4
25.2
25.04
24.86
24.6
12 stone 3
25.3
25.07
24.89
24.7
24.5
12 stone 2
25.10
24.92
24.7
24.6
24.4
12 stone 1
24.96
24.8
24.6
24.4
24.3
If I'm genuinely 5 foot 10, I was a healthy weight as soon as I hit 12 stone 6. If I'm 5 foot 9¾ then even 12 stone 5 wasn't quite good enough. If I'm 5 foot 9½ then I'm still overweight at 12 stone 4, dammit. At 5 foot 9¼ I wouldn't be a healthy weight until I reached 12 stone 2. And at 5 foot 9, which is the shortest I should be, I'd need to get down to 12 stone 1 before my weight loss was a success. By not knowing my precise height, I've entered a proper mathematical grey area.
A difference of just one inch has created a BMI borderline spanning almost half a stone. I knew where I was when I weighed 12 stone 11, but I've since sunk into a woolly zone where I can't be certain if I'm overweight or not. Again the virus wouldn't care one way or the other, but it'd be nice not to have one of the 'underlying conditions'.
In conclusion Body Mass Index is a horribly rough and ready calculation, the vagaries of which don't matter if you're well away from the borderlines. Boris was definitely obese. But I may still be overweight.
