My calculations can't be right?

ruth87jm · June 2014

Hi all,

I've been toying with this question for HOURS and I just can't seem to get my head around it, so I wondered if anyone might be able to shed a little light on where I could be going wrong! :noway:

Basically, I have about 10lbs to lose, and 2lbs a week seems like a sensible target.

I've established that my base metabolic rate is around 1400 calories, so my understanding is that how much I'll burn each day just sitting around not doing much (I work from home so I don't even have to walk anywhere to get to work, so that's a pretty accurate figure I feel!). That's 9,800 calories per week if I wanted to stay the same weight.

Now, if I want to work out 5 times per week and burn 1000 calories per session (I know that's a pretty intense workout), I've added 5,000 calories per week to my allowance, just to stay the same. That's 14,800 calories in total. BUT, I'd need to knock 7,000 calories off this if I wanted to drop 2lbs per week, based on 3,500 calories being equal to 1lb. That leaves 7,800 calories for the week. Divided by seven, this is just 1,114 calories per day.

I can't see where I'm going wrong with the calculation, but that seems to be too low. Just 1,114 calories per day, plus working out hard 5 times per week, just for a 2lb weight loss?

Any advice on what I might be calculating wrong would be much appreciated.

Thank you! :flowerforyou:

Ready2Rock206 · June 2014

For someone with only 10 lbs to lose, 2 lbs a week is completely unrealistic. More like 1/2 lb a week would be ideal.

BigT555 · June 2014

For someone with only 10 lbs to lose, 2 lbs a week is completely unrealistic. More like 1/2 lb a week would be ideal.

this. it seems low because your BMI at that weight is already low, so you need to have a small deficit to make this sustainable

2lbs/week is huge. too many people think of this as a small amount when in reality it is quite large and unless you are really overweight its hard to acheive

Aaron_K123 · June 2014

I have about 10lbs to lose, and 2lbs a week seems like a sensible target.

2 pounds a week is an overly aggressive unrealistic target. I would aim for 0.5 pounds per week.

I've established that my base metabolic rate is around 1400 calories, so my understanding is that how much I'll burn each day just sitting around not doing much

Your basal metabolic rate is actually what you burn if you were in a coma. For "sitting around not doing much" you should add another 200-300 to that number so its more like 1650.

Now, if I want to work out 5 times per week and burn 1000 calories per session (I know that's a pretty intense workout)

Are you at high aerobic cardio heartlevel for a straight 2-3 hours? If not you are probably overestimating your burn there.

Now, if I want to work out 5 times per week and burn 1000 calories per session (I know that's a pretty intense workout), I've added 5,000 calories per week to my allowance, just to stay the same. That's 14,800 calories in total. BUT, I'd need to knock 7,000 calories off this if I wanted to drop 2lbs per week, based on 3,500 calories being equal to 1lb. That leaves 7,800 calories for the week. Divided by seven, this is just 1,114 calories per day.

You are right, that is far to low. That is because 2 pounds per week is way overly aggressive.

Here would be my version.

Your BMR is 1400. Your NEAT (non-exercise activity thermogenesis) or the amount you burn from normal activity is probably like 1650. I am not sure what you are doing to burn 1000 calories but I'm going to cut that in half and say you are burning 500 or 2500 per week. So 2500 per week plus 7*1650 is ~14,000 a week for maintenance. Cut out 1750 for 0.5 pound per week loss and that is 12,250 per week which is That would mean you should eat 1750 per day to lose 0.5 pounds a week at your current activity level.

If you are actually somehow burning 1000 calories per day for 5 days that would be an extra 2500 calories a week or an extra 350 per day which would mean you should be eating 2,100 calories per day to lose 0.5 pounds per week.

I'd want to know what you are doing to burn so many calories though especially since you don't look very large. For myself I consider myself to have burned 500 calories after doing probably 70 minutes of intense cardio and I am a lot bigger than you.

psuLemon · June 2014

Here are some realistic goals

If you have 75+ lbs to lose 2 lbs/week is ideal,
If you have 40-75 lbs to lose 1.5 lbs/week is ideal,
If you have 25-40 lbs to lose 1 lbs/week is ideal,
If you have 15 -25 lbs to lose 0.5 to 1.0 lbs/week is ideal, and
If you have less than 15 lbs to lose 0.5 lbs/week is ideal.

If i makes you feel better, the average women I know that is working out 5 days a week is losing at 1700-2100 total calories (depending on age, height and weight). At this point, concentrate on weight training with some minor cardio. If your goal is to tighten your body up, then muscle preservation is key.

MinnieInMaine · June 2014

What Aaron said

ruth87jm · June 2014

Thanks guys, that's all very useful.

In reality, you're right, I don't know exactly how many calories I'm burning - I was estimating basing on things I've read, and I was planning on upping the ante over the next few months. I've just ordered a Polar watch though so hopefully that'll give me a better number to be working with.

Thanks again!

Aaron_K123 · June 2014

Thanks guys, that's all very useful.

In reality, you're right, I don't know exactly how many calories I'm burning - I was estimating basing on things I've read, and I was planning on upping the ante over the next few months. I've just ordered a Polar watch though so hopefully that'll give me a better number to be working with.

Thanks again!

Just out of curiosity what do you do for exercise?

How long?
What sort of activity?
How hard is your heart beating? (Can you talk during it?)

You can sort of ballpark it with that info. Honestly I think heartrate monitors are overly trusted. I have an HRM and most of the time I don't believe it. I leave it for others to comment on this but I've worn the heart rate monitor set to the correct settings and had it tell me I burned 950 calories in 58 minutes of exercise which seems ludicrously high to me so I cut it in half. So far my weight loss has been tracking with expectations and I typically consider 1 hour of intense cardio to be about 500 calories burned.

bwogilvie · June 2014

Honestly I think heartrate monitors are overly trusted. I have an HRM and most of the time I don't believe it. I leave it for others to comment on this but I've worn the heart rate monitor set to the correct settings and had it tell me I burned 950 calories in 58 minutes of exercise which seems ludicrously high to me so I cut it in half. So far my weight loss has been tracking with expectations and I typically consider 1 hour of intense cardio to be about 500 calories burned.

I did some research into HRMs last summer after comparing notes with my wife. We did a 38-mile bike ride together, with about 1200 feet of climbing, at an average 12 mph speed. My Garmin Edge 800 claimed I consumed 999 calories, while her Polar HRM claimed that she consumed over 1,700. Since I weigh more than she does, I should have consumed more energy than she did; I'm probably slightly more biomechanically efficient when cycling than she, and I have a slightly more aerodynamic position on my bike, but that shouldn't account for more than a 5-10% difference. Obviously at least one of those HRMs was way off!

Then I turned to Pubmed and checked out the peer-reviewed research.. One study of the Polar F6 showed that, even calibrated with subjects' actual VO2max and HRmax, it overestimated energy expenditure by 27% (http://www.ncbi.nlm.nih.gov/pubmed/21178923). An earlier study showed that the Polar S410 overestimated energy expenditure in women by 12% (http://www.ncbi.nlm.nih.gov/pubmed/15292754). Another study found that the Polar S810i overestimated expenditure when exercising lightly but not moderately (http://www.jssm.org/vol9/n3/21/v9n3-21abst.php). The research seems to suggest that HRMs are less accurate for women than they are for men.

The study by Keytel et al (http://www.ncbi.nlm.nih.gov/pubmed/15966347) that produced a widely-used formula found that it was reasonably accurate for groups when VO2max had been measured, but less accurate without measurement of VO2max - in the latter case, over 26% of the variance in energy expenditure was not explained by their equation, which uses heart rate, gender, age, and weight to estimate calories consumed.

The few HRMs that use Firstbeat's algorithm, which uses changes in timing between heartbeats to estimate energy expenditure (not just the average heart rate over a longer period), might be more accurate. Garmin and Suunto sell units that use it, including the Edge 800 and Forerunner 620. Firstbeat's website gives more details.

My calculations can't be right?

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