Thursday, February 02, 2012

Calculating BMR

My earlier post got me thinking about BMR a little more and I did a quick bit of maths! I know, 8:00am on a Thursday morning and I'm doing maths, it's not a good sign! Anyway, here's a graph of my BMR profile according to this BMR calculator.

Now I don't know how accurate this calculation is, but as you can see from the simple data set I used, BMR falls in a nice neat straight line with age. I've made no allowances for changes in fitness, I've just let the BMR calculator do the work, so whatever equations it uses, I've used!

I put in my height as it is when I stand up straight and again without allowing for shrinkage over time! I've also used a fixed weight which is probably a bit low for me, but one I'd like to be. No harm in having a dream. Given it's a straight line, changing the weight would simply shift the line up or down.

If you do a bit of simple maths, the calorie count drops by about 7 calories a  day each year. Not much is it? It's 49 calories a week or 2555 calories a year. If I remember correctly, 1lb of body fat is something like 3500 calories. Now it starts to add up. If you are eating the same amount of calories now as you were 30 years ago, you're almost certainly taking in more than you're using up. Unless you are dramatically more active, you could easily be 200 calories a day over your BMR, which is 7300 calories a year. Equivalent to 2lbs of body fat!

Now I'm not talking as an expert and there might well be something intrinsically wrong about my maths here, and if not the maths then the science or the logic! For one, I'm not wholly convinced that BMR is a straight line. If it were, my BMR at 20 would have been 2049. Maybe it was and I was just very active. But at this simple level, knowing your BMR would seem like a very useful bit of information!

It's all a bit sobering isn't it.

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