6/19/13

The math behind weight loss (and why MyFitnessPal kind of sucks.)

The simple version goes like this: calories burned must exceed calories taken in. To do this, we need to be tracking every calorie we consume, and we must know how much we should be eating.
To determine how many calories you should be eating, here are two calculators:

BMR: Basal Metabolic Rate

BMR: The amount of calories you burn only at rest. This means if your BMR is 1300, you burn 1300 calories per day without even getting out of bed. Calculate your BMR here.
You should never eat less than your BMR because your metabolism will actually slow down, causing your body to go into starvation mode so that any weight that you do lose will be muscle weight, not fat weight. (And you don’t want to be “skinny fat”!)

Activity Level

Clearly this will be an estimation unless you plan on logging every workout (and monitoring calories burned in said workouts with a heart rate monitor EVERY TIME), as well as calculating how many calories it takes to walk around the house, do the dishes, go to the bathroom, etc etc. Since this is basically an impossibility, we use calculators and equations to estimate.


To estimate our activity levels, we calculate our daily caloric needs via this ACE approved calculator that asks you to choose how active you are on a continuum of sedentary to highly active.

The outcome is a number of calories that you need per day to maintain your current weight, exercise and daily activity included.

Activity Level in the MyFitnessPal app.


Disclaimer: If you’re only using the MyFitnessPal app to log your food but you don’t log your exercise, you’re not using the app correctly. The app asks you to estimate your daily activity levels in your job. At no point does it ask about exercise, because it assumes you will log your exercises daily.
Here, you have three options:
a. Use the app the way it’s intended to be used by logging every single workout (using MyFitnessPal’s calories-burned estimator OR your exact amount of calories burned by using a heart rate monitor)
b. Account for your regular exercise when it asks you for your daily activity levels. This is basically a guessing game and why I don’t particularly like MyFitnessPal; Your numbers won’t be incredibly accurate because everyone burns calories at a different rate.
c. (what I do) If you don’t plan on logging your workouts, determine your ACE recommended Daily Caloric Needs here and then override the numbers in MyFitnessPal (in net calorie goal).

Now, if you recall, this number we have put into MyFitnessPal is the number of calories that you need to consume to maintain your current weight.
Lets assume from here on out that you’ve overridden your Net Calorie Goal with the ACE Daily Caloric Needs number.
So how do I lose?
To lose weight, we need to create a caloric deficit.
To safely create that deficit, we need a number between our BMR and our Daily Caloric Needs number. A safe amount to lose (without screwing your metabolism) is 1-2 lbs per week.
If you want the math, here it is….1 pound of fat is equal to 3,500 calories, so to lose 1 lb you have to create a 500 calorie deficit per day (500 x 7 days/week = 3500 calories). This means eating 500 less calories than your ACE daily caloric needs number (or 1000 less per day if you’re trying to lose 2 lbs per week). Remember, your normal exercise is already accounted for in your chosen activity level, so to create that deficit you must eat less, or adjust your exercise output and exercise more than normal.
To reiterate, in order to lose 1 lb a week, create a 500 calorie deficit each day by eating less and exercising more. (Which could mean either eating 500 calories less per day, OR eating 300 less calories but adding an extra half hour or so onto your normal workout routine.)
So, for a real-life example, if my daily caloric need is estimated at 2,300 (I am very active, and this number reflects my workouts), then I need to eat 2,300 calories to maintain my current weight. If I want to lose weight, I would reduce my calorie intake by 500 (or reduce by 300 and burn an extra 200 at the gym on top of my usual workout).

Get to the point.

The point of this post is not to give you a headache.
The point is that if you’re using MyFitnessPal to log your food but not your exercise, your numbers are probably skewed. Example: If you don’t log your workouts and have a desk job, you probably chose “lightly active” or “sedentary”, but since your workouts aren’t taken into consideration, MyFitnessPal is probably telling you to eat less than your BMR which could be doing harm to your metabolism.
If you’re using MyFitnessPal, the best way to do it is by tracking your workouts using your heart rate monitor’s calorie count and making absolutely sure that you’re logging EVERYTHING, every time. This is the only way it doesn’t suck.
If you aren’t logging your workouts (I don’t, personally) you can and probably should still use MyFitnessPal because logging your calories is incredibly important to weight loss, but make sure you’re doing it right: calculate your BMR and daily caloric needs in the calculators above, compare them or override the generic numbers that MyFitnessPal gave you, then adjust your eating and exercise habits accordingly.
And never, ever, no matter what MyFitnessPal tells you, eat less than your BMR!

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