Wednesday, February 9, 2011

It's all about the math.

I like math. (went to math camp 5 years in a row. I really like math.)

Numbers make sense to me. Numbers make things simple.

Today I'm breaking the numbers down so I have a plan.

The beautiful thing about weight loss is it is all about the math. No - you cannot predict the exact amount of weight you will lose in a week. Incidental exercise, temperature, hormones ... these things all play a part. But you can get a pretty good idea.

Weight loss in theory is simple. Calories in - calories out. That's it. It's all the other stuff we tie to weight loss such as our emotions, our supporters and our sabateurs that make it tricky.

But as for the math
The basal metabolic rate is basically - in laymans terms the amount of calories your body uses up in a day "just being". To calculate this go to and click on the tools

Right now my BMR is 1517 calories. This will drop with weight loss.

Our food intake for the day is 1200 calories

To lose 1kg a week I need to have a deficit of 7000 calories a week.

That is the food I take in, minus the energy I burn x7 days must be 7000 calories.

1200- 1517 is a deficit of 317 calories a day or 2219 calories a week.

To lose 1kg a week I need to burn an additional 4781 calories.

That means I have to work.

If I have one rest day a week, I need to burn on average 797 calories a day. That is a LOT for me!

This is why weight loss tends to slow as you get slimmer. Your BMR drops as your weight drops. Which means to sustain weight loss you either need to eat less (not recommended as 1200 calories is on the low end of the scale) or move more.

I am going to have to move!

My plan
Monday - Double class. Group Power + Zumba + cardio before the first class = 1000 calories
Tuesday - tap class - 300 calories (I am going to suggest my friend and I go for a 30 min walk while we are waiting for the girls to finish ballet to burn a few extra!)
Wednesday - a run day. Aim is for 700 calories
Thursday - Double class. Group Power + Zumba + cardio before the first class = 1000 calories
Friday - run day - aim is 500 calories
Saturday - Super Saturday session - this is the big ask. If I haven't made up extra calories in the week I need to burn 1281. But it CAN be done!

This is ideal. No week is ideal. But it gives me a plan. My goal is so close I can taste it. I haven't been in the healthy weight range since I was in my very early 20s. And I am so going to be there again! I love my double class days. Which is a good thing ... since they are calorie burners.

And my job as a nurse helps too. We walk an incredible amount.

But I like to break the numbers down. It's all about the math

**** ETA ... a fall apart Thursday afternoon due to a tired girl and her needed some "chillaxing" after school has drummed home to me the importance of flexibility. Especially as I am an on call shift worker. So the new plan is - if i am not working I need to get a morning walk in EVERY day *even the "rest" day*. This should give me 200 cal a day ... 1400 a week and a LOT more flexibility in my routine!****


  1. Oh My Goodness.
    Kath - you have just given me one of those 'Click' moments. I just followed your whole step-by-step calculations to work out my own numbers and it's NO WONDER I'm not losing 1kg a week.

    Here I am thinking I'm being good exercising hard and burning 400 - 500cal maybe 5 days a week... But not losing more than 500g or so.

    Apparently I need to be burning 880cal p/day (eating 1300 cal which is what I've been doing... might change that to 1200 soon!).

    Wowee. Thank you for stepping out the math/science behind it. I can now plan my exercise more effectively.

    Fantastic. Thanks.

  2. Yep. See that is why i like math. Its ok to loose less than a kg a week. Its likely i will lose less. But i like to know why. I am the only person who can affect my weight loss and this is why. The math.

  3. Wow...

    I failed maths dismally so thank your for explaining about this so I can understand it better.


  4. I like numbers too. That's why I've succumbed to buying a HRM, and I wish it would hurry up and arrive so I can do a similar plan!

    Is there anywhere you can walk to during the week to add in a few extra calories burned? Shops, school, work, the gym. If you burnedeven an extra 100 a day walking it would take the pressure off Saturdays.

  5. Ha thanks for that maths lesson.... you know what?? It makes sense so thank you & for sharing your journey.
    Nic newbie 12wbt

  6. Sorry If i'm a bit slow (really suck at maths! and anything maths related...) I cant understand where the "To lose 1kg a week I need to have a deficit of 7000 calories a week" comes from?
    Does that 7000 apply to everyone who wants to loose 1kg a week?
    Sorry this may seem simple to some of you, but I just cant seem to get my head around all the numbers.

    Thanks for your post though, Its FANTASTIC!! (and for your help) ;)

    Cheers, Tash (new 12WBT member)

  7. Tash Hi! Welcome to 12wbt!

    SOrry I didnt reference that figure! In Crunch time Michelle quotes that you need a 7000 cal deficit to lose a kg a week. a 3500 cal deficit to lose .5kg a week.

    So yes it does apply to everyone - but remember it isn't an EXACT science

    Hang in there - it's all confusing to start but it's going to be FUN!

  8. Love your enthusiasm Kath, it always makes me feel better when I'm having a crappy day (or week, as it is right now). Love your math, and think I need to work out mine....