The Diabetes Formula – by Helen May


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I trained as an engineer and before that I was one of those rare kids who enjoyed maths at school. So when I was diagnosed with diabetes, I was always after a formula to work out how much insulin to take. At first, the nurse gave me simple instructions for dosages with examples: “2 units for a slice of toast”; “4 units for chips”, etc. But that only helped if I was eating something she told me about and if I remembered the numbers.

So I was very happy when a locum diabetes consultant spotted the mathematician in me and gave me a formula: 1 unit of insulin for every 10 grams of carbohydrates. From then on, all I needed to do was guestimate the amount of carbs in my food, divide by ten and dial up.

Unfortunately, I soon realised it’s not that easy: there are other factors which affect my blood glucose: amount of insulin taken, how much exercise I’ve done, any alcohol I’ve drunk and good ole stress. So, I started to apply my inner mathematician to create the complete formula. With my knowledge of insulin, diabetes and blood glucose, I came up with a formula…

Finally, my inner mathematician was satisfied. Time for the engineer to step up. One of the differences between the two roles is application. An engineer wants to apply the formula and, to do so, the engineer needs some numbers.

Some numbers are easy to come by: I have meter to tell me my blood glucose at a particular moment in time; I have a watch to time since I last ate, last took insulin, last exercised, etc; I can wear a heart rate monitor to observe how intensely I exercise; and I can look up the glycaemic index (GI) and insulin profiles on the internet.

Others numbers are more challenging. For example, how do you measure stress? You know, the feeling you get when you are scared half way up an exposed climb or a high profile meeting at work or, like Jenny’s son, Ewan, a reading test at school. To be honest, I don’t even know what units you’d use to measure this type of stress: it’s not Pascals, the SI unit of stress (I warned you I was an engineer).

So if I had my meter, a stopwatch, a heart rate monitor, access to the internet at all times, a clever dude who could help me measure stress and kept track of all my food, exercise and alcohol, I may be able to calculate my blood glucose and accurately calculate how much insulin I need to take. That’s a lot of “ifs” and, in reality, ends up with lots of approximations. The disciplined engineer in me doesn’t like this: it likes definite numbers.

I started this blog with the hypothesis that, as an engineer, it is easier to manage diabetes. By the end, I’ve decided all the approximations I have to make along the way outweigh many of the advantages of knowing what affects my diabetes. So my engineer (and mathematician) needs to remember that an intelligent approximation is better than nothing and not to beat up the diabetes when it doesn’t behave according to my formula.

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