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Weight Loss Math

Every time I try to lose weight, I find something to hang onto when things get tough (as they always do). This time, it's math.

I've tried the "just eat healthy" and the "just move more" and even Weight Watchers, because the points system is pretty cool. But this time around, I'm counting the calories, old school style. And I'm kind of loving it. To understand why, I'm going to share some of the math and try to explain why it can be more than a tool for weight loss -- it can be empowering. And simple.

The magic number to gain or lose a pound is 3500 calories (this is being disputed, and can vary, but we're going with it). However, to do anything with this number, you have to figure out how many calories your body burns on a typical day, outside of any workouts. I always use an online calculator for this. Here are the numbers that FitDay.com gives me:

Age: 26
Height: 5 foot 5
Sex: F
Current Weight: 182 lb
Exercise Level: Fairly sedentary (desk job)

FitDay estimates that I could eat 2235 calories a day and, provided I didn't do any extra exercise either (a workout, a long shopping trip, etc) never gain or lose a pound. Let's call this 2200 calories, and that's my base.

Now, you've probably heard that it's not "healthy" to lose more than 2 pounds a week (at least without medical supervision). You may also have actually tried to lose weight before, managed 1-2 pounds a week, and still felt frustrated. So let's look at the math.

Each day, I will log all of the calories I eat and all of the calories I burn through workouts (or any activities above what I would do on a typical day). You then compare this to your base, and over several days, to that magic number, 3500.

Let's plan to eat 1200 calories a day (pretty low, but doable!). At the end of a day, that's 1000 calories I did not eat (a 1000 calorie deficit). When I reach a 3500 calorie deficit, I can expect that the scale will show me a loss of 1 pound.

1200 calories / day = 1000 calorie deficit x 3.5 days = 3500 calorie deficit

Yep. I can lose 1 pound every 3.5 days (or 2 pounds every 7 days) without working out -- if I am really careful about what I eat. (Note: Since you should be weighing yourself in the mornings, you may actually see the change every 4 days. If you try to weigh yourself at noon, you may see false excess weight.)

Why is this empowering? I mean, there are reasons to find this frustrating. If you can't manage so few calories and can't work out often, your progress is going to drag. But there are reasons to love this, too.
  1. You can't beat up on yourself for not losing, like, 5 pounds a week. I mean, look at the math! You'd have to eat a deficit of 17,500 calories. At the maintenance number above (2200), you only even need 15,400 calories a week to maintain your weight. This means that you'd not only have to not eat any calories per day (which, hello, is a bad plan -- fat is better than dead, yes?) but you'd then have to actively burn (meaning, through extra activities like workouts) another 2100 calories in that week (so like, 4 1-hour intense workouts). People who do get these numbers are often losing things like water weight, muscle mass, or are utilizing a team of doctors, chefs, and personal trainers. Relax.
  2. If you know the math, you know your choices. Let's say you want to eat a bit more, either on a daily basis, or for a special occasion. Okay. Now you know exactly how many calories you have to burn through workouts. If you want to up the weight loss from ~8 pounds a month to ~10 pounds a month (an extra half pound a week), you have to burn 1750 calories a week (or 3.5 workouts that burn about 500 calories each, or more workouts that burn fewer). The point is, you can set very concrete workout and food goals and know exactly what to expect when you do or do not meet them -- no hopping on the scale and wondering why it feels like you've been suffering and trying and striving forever and it still hasn't budged.
  3. You can see into the future.
Okay I'm going to develop this future argument in greater detail using my own stats.

Start Weight / Date: 182 pounds, September 7, 2012
Goal Weight: 120 pounds
Pounds to lose: 62

Now, technically, as I drop weight, I will have to adjust the math. When I weigh, say, 130 pounds, I can't subtract from 2200 anymore because it won't be my baseline. But let's pretend that I use a combination of calories not eaten and calories burned (diet and exercise) and never encounter any setbacks (i.e. a perfect world...). In this world, I'm getting my 1000 calorie deficit each and every day, always.

Perfect World to Goal Weight: 62 / 2 = 31 weeks or ~ 8 months

That sounds like a long time, and this is where the frustration might rear up. Like, really, if I starve myself every day for 8 months, I'll hit my goal weight? Not worth it!

Okay but think about it. My goal weight is really ambitious. I mean, it's not like I'm not going to be happy until I reach it. Let's continue in our perfect world for a little while here. (Why? I know I won't make the perfect world, but I think it is important to know what is the absolute maximum that you can realistically expect, otherwise it is tempting to beat yourself up for not having met what is actually a totally unattainable goal.)

I also don't have to "starve myself." If I do workouts, I can eat more and achieve the same pace. Or, I could eat the same, workout, and actually achieve a faster pace (or the same pace if we assume I do slip up sometimes). Let's do some math, though, assuming just the 1000 calorie per day deficit.

Okay so at 182 at my height, I am just into the Obese category (ew... I don't feel that big...). As soon as I hit 179, I will officially no longer be obese.

Perfect World out of obesity: 1.5 weeks

So... how is that not worth being a little extra hungry? For a week and a half? To not be obese anymore...

When I hit 149, I will officially no longer be overweight. This is a major goal of mine.

Perfect World to normal weight: 16.5 weeks (or ~ 4.1 months) (aka, around New Year's!)

But of course, I'd like a bigger buffer between me and "overweight," since if I started maintenance, I could expect my weight to fluctuate a bit throughout any given month, putting me back into that category pretty often. So let's say 135 is my real goal, and 120 is my "in my dreams" goal (because why not dream big?).

Perfect World to realistic goal: 23.5 weeks (or ~ 5.9 or 6 months) (or before spring!)

And I could pepper my life with tons of smaller goals to celebrate, too. Every 5 or 10 pounds. Every milestone like, say, 20 or 25 or 50 pounds lost. Every month on the program. Every 3.5 days I could celebrate losing a pound; every week, 2. Every month, 8.

But let's dip out of the perfect world and I'll show you why the math is still cool. Let's say my progress is a whopping 50% of the ideal -- due to vacations, deviations, stress, parties, holidays, mysterious genetic forces plotting against me, whatever. I lose, on average, 1 pound a week instead of 2 (some weeks 2, some weeks 0, for example).

50% Slower out of obesity: 3 weeks

Okay, so in three weeks, I won't be obese anymore. That would still be amazing.

50% Slower out of overweight category: 8 months.

Okay that is way less encouraging! But you know what, if I do nothing, in 8 months, I'll probably have gained more weight. If I do this, in 8 months, I'll be back into a size 10 and wearing that really cute purple pencil skirt and tighter tops and feeling great because I'm no longer overweight -- I'm officially (if barely) healthy.

50% Slower to realistic goal weight: 1 year

Okay so a year from now, I could be at what might be the perfect weight for me, even if it is not my dream-big vanity weight. I honestly think I could be very, very happy at that weight. I'd be maybe a size 7 or 8, and that's pretty sweet, actually!

50% Slower to dream weight: 16 months (1 year and 4 months)

But I could still make my dream weight, and long before I turn 28!

So the good news? As long as I try my best and don't willfully go off my diet, the worst case scenario is that it takes me 16 months to reach a vanity weight, or 1 year to reach a pretty happy medium. But if the "perfect world" math isn't likely, then neither is the worst case. Most likely, I'll hit my goal marks somewhere in between.

The math will help me have realistic expectations. It will help me dream of a thinner, fitter, healthier, realistic future. Those numbers are as real as finishing your degree (provided you study and hand in your work) or getting your paycheque (provided you go to work, meet your deadlines, etc). They will really happen if I do the work.

The math will help me make choices. I can choose to take a week off my diet if I want and not gain back because I will know my baseline. I could choose to speed it up at some point to meet a particular mini goal faster, then slow it down later to have a breather or accommodate special circumstances. I can see exactly how my choices will affect my longer term goals -- and learn to be okay with it. I can learn to celebrate what I'm doing well because I'll really appreciate it, rather than beating myself up over not reaching goals that are not attainable anyway. When I'm hungry and experiencing cravings, I can go for the fruit instead by telling myself that if I do, in 3.5 more days (or less!), I'll be down another pound. When I don't want to do a workout, I can remind myself of that extra pound or two this month (going from a loss of 8 to a loss of 10 is pretty cool!) if I just put on the workout clothes and go do it.

The math won't just help me reach my goals in an abstract way. It will reassure me, motivate me, inspire me, comfort me.

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