Sums don't add up

KNoceros

I've been on MFP for about two years now and have managed to lose 10kg. I've passed 2 goal weights and am nearly ready to start maintaining. Being a curious, data hungry sort of person I got a Fitbit for Christmas to try and help work out the CO side of the equation and allow me to eat a little more freely.

My query. Since 1st Feb my total calorie deficit is allegedly 6856, which I'm quite pleased with and should give a weight reduction of about 860g. However, I've actually lost over twice that.... can anyone explain why?
Its not likely to be water as I've been at this for 2 years, and I weigh my food but on a balance scale so am more likely to be over- rather than under- eating.


For those that are bound to ask (although not relevant to this query) 39F, 5'5" SW 73.3kg CW 63.2 (GW 62.6)

seska422

Everything is an estimate. Calories in food and drink, calories burned, your BMR, your TDEE, everything. There's no way to get exact numbers for those.

Online calculators basically give you a starting point. You start from there and then figure out your personal results through experimentation.

TimothyFish

Outside of a lab you aren't going to get precise numbers for calories out or calories in. On top of that, February 1st was just a few days ago, so it could easily be water weight that you lost during that time that explains the additional weight loss. Just because you've been doing this for two years doesn't mean that your fluid levels won't fluctuate. You can lose the amount of water that we are talking about just by going out for a run.

Hello_its_Dan

Math generally fails in an organic system

CattOfTheGarage

Yes, either you are underestimating your exercise calories or overestimating your food. Yes, a balance scale is less precise than digital, but it doesn't follow that that means you will overeat. If you are concerned about the error and thinking about it a lot, it may well cause you to undereat.

As for the exercise burn, are you sure the Fitbit is set up right and is not underestimating?

courtneyfabulous

Fitbit is notoriously inaccurate. Luckily you've lost more than it predicts- some people get frustrated because they've lost less than they should have according to their fit bit...

TDEE and calorie burn are always just an estimate, actual results will vary.

Plus some part of weight loss is always water since excess body fat causes water retention in the body so as you lose fat you will retain less water, even if you've been at this for years that's just how fat loss works. The equations for weight loss are based on calories and fat alone and don't take into account that you will lose water weight in addition to fat (and also very likely some muscle too).

courtneyfabulous

Dan_Rollins_ACE_PN wrote: »

Math generally fails in an organic system

This sounds like something Ian Malcolm would say

KNoceros

Thanks guys. Not stressing, more curious and surprised that the discrepancy was as large as it is. I had sort of expected 20-25% (in either direction) rather then 100%! Still as several of you have noted at least it's in my favour so far!!

Tacklewasher

Congrats on being within spitting distance of your GW. But I think the difference is easily explained as "noise" in that your body may have had excess water Feb 1 that you've since lost, or it was closer to TOM (if that applies). I easily can go up or down 1-2 lbs day to day. Had sushi for lunch Thursday, was up 1.3 Friday morning and down 1.2 this morning.

Has your loss over the last 2 years been more consistent than that?

KNoceros

Thanks all for the explanations.

My comment regarding balance scales was related to the fact that it's very tempting to add "just a tiny bit more" and push it past level. It also means you can only measure in the smallest increment you have a weight for (5g and 1/4oz). But I like them. They belonged to my gran (with the imperial weights)

I hadn't quite twigged that even after the initial water-loss it would still fluctuate. Which is stupid really, because I can see in my data the nights that I had a chip supper (with lots of salt) and the days after I exercised loads. Or flew. Planes really make me hang on to water.

When I've got a few months of good data, I'll go back through and do the sums again. I'm curious to know how accurate (or not) the estimated burns are and how good I am at logging.

Thanks again for your insights. Sorry for being dim.

CattOfTheGarage

Remember that it's not a 100% error in your whole food intake, it's a (potential) 100% error in the deficit. Let's say your calorie goal is 2000, and you were aiming for a deficit of 500 but you got it wrong and ended up with 1000 instead, that means you took in 1500 instead of 2000. That's a 25% error in your net intake. If you got your food wrong by maybe 15%, then underestimated your exercise by another ~200cal per day (easy to do if you're active and being cautious), there's your error (these numbers are approx but you get the idea).

I am inclined to agree, though, that a lot of it is water weight fluctuation. I'd want to see more like 4 to 6 weeks of data before concluding you were losing twice as fast as expected.

Tacklewasher

kathrynhoward84 wrote: »

Or flew. Planes really make me hang on to water.

The last time I flew was the worst. I've NEVER had swollen ankles before. I was so happy that I didn't have to suck in to do up the belt (I've almost asked for the extender before), but *kitten* did my ankles puff out. Wife commented when I got home and went to bed.

Anyway, keep at it and you'll get that last little bit gone.

PAV8888

Use a trending weight app or website.

Since you now have a Fitbit account you can automagically connect trendweight.com and use your account to even enter previous weigh ins

prattiger65

I don't think 18 days is enough time to see any trend.

Tacklewasher

Guys. They are .6 kg (1.3 lb) away from their goal weight. Please keep that in mind with any advice you give.