Sport Bad math on fitday - here's good math

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malkore

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So, I figured out that Fitday.com's math appears to be fudged when they calculate calories beyond BMR...that is, what you choose for "lifestyle" on the Home tab.

Choosing bedridden should not increase daily calorie intake. the BMR multiplier should be 1.0. But fitday actually uses light activity multiplier 1.2 instead.

Essentially, this means that you pick an accurate lifestyle, but fitday's math multiplies by .2 MORE than it should, giving you a slightly higher maintenance calorie value than it should.
Thus when you strive for 500 cals under that amount, you're not really 500 cals under your real estimated maintenance.
Then you don't get that 1-2lbs lost per week that other people get.
You get frustrated, and maybe even give up, or cheat on your diet in a bout of depression.

I've emailed fitday about this 'discrepancy' I believe exists.

Ergo, to help any of you ladies out, I'll provide all the formulas you need to get a realistic daily maintenance. Fitday's food tracker is fine, it's the 'activities' page that's off.

First off, we can estimate your ideal body weight, or IBW.

IBW = 100lbs + 5lbs for every inch over 5' tall. So a 5'4" woman's IBW is 120lbs. If you're light framed, this might be a little lower, wider framed women, cut yourself a little slack :)

Now, if you're over 125% of your ideal body weight, we'll have to adjust the weight we use in your BMR calculation. So, say our previous example of 5'4" is actually 160lbs.

Current weight / IBW = % of ideal
example: 160/120 = 1.33 when expressed as a percentage is 133%

She's over 125% (or 1.25) so we do need to adjust her body weight for our BMR calculation.
To find Adjusted Body Weight
Current weight - IBW x .25 + IBW

160 - 120 x.25 + 120 = 130lbs

For Women

BMR = 655 + (9.6 x weight in kg) + (1.7 x height in cm) - (4.7 x age)

So for our 28 year old girl of (adjusted)130lbs (59kg) at 5'4" (162cm) it comes up to:
BMR = 655 + (9.6 x 59kg) + (1.7 x 162cm) – (4.7 x 28)
BMR = 1365 calories per day

Now we just add your 'lifestyle' calorie needs in by multiplying BMR by anywhere from 1.0 to 2.0.

Activity level factor


Activity level

1.0 Sedentary - essentially bed ridden.

1.2 Very light activity - nothing physical. Working a desk job or on a computer and not performing any type of physical activity during your day.

1.4 Light activity - having a non-physical job (desk, computer, etc.) but performing some sort of physical activity during the day (e.g. above average walking) but no hard training.

1.6 Moderate activity - having a non-physical job, performing some sort of physical activity during the day, and including a daily workout session in your routine. (if you're already in decent shape, and working out with weights or cardio about an hour a day, this is where you'd be at)

1.8 High activity - construction worker, and almost daily training.

2.0 Extreme activity - a very physical job and daily hard training.

so say 1365 x 1.4 = 1911 cals for a daily intake for our 28 year old 5'4' 160lbs woman. and since we already adjusted BMR to a weight close to her 'ideal' weight, we shouldn't even need to cut it by 500 cals to achieve weight loss. As long as she gets 30mins of exercise a day and eats healthy foods, she should lose weight.


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Ok I hope that wasn't too complex. But I started to question fitday's reasoning why I need 3128cals a day to maintain my current weight and how they thought I could burn 1380cals a day sitting at a desk job all day.
 
I never use fitday's caloric expenditure system, only to track consumption.
 
Because it always seemed too high to me, I never really did either, but I finally decided to 'get down to the truth'.

At first I thought it was skewed because, right now, I'm not at my slimmest. But I had my wife run my numbers (she's a dietary technician at the Neb. Heart Institute), and her number matched my numbers...but fitday was way off.
Fitday will do your BMR correctly if you're not 125% over ideal weight, but those 'lifestyle' modifiers are way way off, adn I'm sure some of our less knowledgable members here would fall prey to those misleading numbers.
 
I'm glad you posted this. I have also noticed that Fitday seemed too high, but never sat down and put the math together.

Here is the math for me....
Fitday (bmr) = 1591
lifestyle (housework) = 1352
Total (before specific activities) = 2942

Miftlin St. Joer equation
BMR = 1528.35
Activity level (bmr x 1.55) = 2368.94 (2369)

Harris-Benedict
BMR = 2456.35
Activity level (bmr x 1.55) = 2456.35 (2456)

As you can see, subtracting 500 kcals from what Fitday sais is my BMR, would only get me to roughly what the other equations show as my BMR.

Also, adjusting it using the equation you posted, then calculating using Harris-Benedict, it comes out to...
BMR = 1439.30
Activity level = 2230.92 (2231)

I am interested in why the adjustment? I was under the impression that BMR was based on actual body weight, not ideal body weight. Then multiply that by approximate activity level, and subtract calories accordingly for weight loss. Is the adjustment a way of personalizing the caloric deficit instead of subtracting the standard 500 kcals?
 
deschain said:
I am interested in why the adjustment? I was under the impression that BMR was based on actual body weight, not ideal body weight. Then multiply that by approximate activity level, and subtract calories accordingly for weight loss. Is the adjustment a way of personalizing the caloric deficit instead of subtracting the standard 500 kcals?
Click to expand...

I was wondering about this too. I'm roughly 120%-123% over ideal, so I should be calculating based on my ideal? Never heard that before.
 
My wife is a registered dietary technician, and the adjusted bodyweight for BMR is apparently how it's supposed to be done. its in her text books and is how her instructors did it, and is how the dietician at the hospital does it too.

My wife is not a slender woman. She is 245lbs right now, but losing it (some health issues lead to a steady weight gain). And about 5'8", and is gonna be 25 in a few months.

If I plug 245lbs into this equation for BMR:
BMR = 655 + (9.6 x weight in kg) + (1.7 x height in cm) - (4.7 x age)

I end up with a BMR of something like 2400+ calories for her, and if we use a 1.4 multiplier it takes her up over 3,000 calories for a job where she does a lot of standing, and some walking.

3,000cals a day is just going to keep her at 245lbs! She's essentially 180% of her ideal weight, so when we use her adjusted body weight of 135lbs, we end up with about 2,000 cals a day including her 1.4 multiplier. A MUCH more realistic number. But again you only need to deal with an adjusted body weight if you're over 125% of your ideal body weight...and that's of course assuming its fat weight, not lean muscle mass (not really even an issue for women, but a male bodybuilder could exceed his IBW by 125%, but only be 8% bodyfat..so you wouldn't want to adjust his weight for the BMR calculation)


Did that all makes sense?
 
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Yes, that makes sense.

Has FitDay returned your email? I am interested to hear how they explain the discrepancy.

Also, I have noticed when I enter in a custom food, directly from the label, it is often rejected. A red error pops up stating that the calories should be "X" amount, then shows an equation for calculating calories. That's all well and good, but appearantly that equation clashes with whatever is commonly used to determine nutritional values on labels. Have you ever noticed this?
 
calculating it based on your ideal weight doesn't make sense. my sister and I are roughly the same height but i will have a higher basal metabolic rate than her because i am heavier (and burn more calories doing the same things because i am shifting more weight around with me).

i used the harris benedict method to calculate my calories needed using my actual weight and it works for me.
 
neenaw,

if you use my calculation to see if you're over 125% of your ideal weight...are you?

Like I said, I am using information that dieticians use, and the above formula IS the Harris Benedict formula.

Here, here's my BMR using Harris/benedict:
87.72kg
175.26 centimeters
29 age
BMR = 1946 cals
Light activity (BMR x 1.4) = 2725 cals
Moderate activity (BMR x 1.6) = 3114

and here's my wife's numbers using Harris Benedict (without using adjusted weight):
111.36 kg
170.18 cm
BMR = 1900 cals
Light = 2660 cals
Moderate = 3040 cals

Do you really think her BMR + light work activity is 3000 calories a day??? Mine looks fine, but hers does not, because she is very overweight right now.

So adjusted body weight to 75.5kg:
Adj. BMR = 1556 cals
Light = 2178 cals
Moderate = 2490 cals

Now, doesn't that look way more reasonable for a 24yr old woman who's about 5'8" who's 90lbs overweight right now??

Remember, harris benedict is a BMR estimate, and the raw formula in no way takes into account how fat you are, or how muscular you are.
 
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