Using calories in/out for weight loss

[J3ff]

Howdy all! I'm curious how accurate folks have found the calories in vs. calories out graphs with respect to weight loss, or maintaining. (I have the Charge 2 with heart rate). I'm asking because I've found it helpful, but not always so accurate maybe?  Since Sept 2016 (6 months ago) I've lost 45 lbs, and I have another 20 to lose. I enter everything I eat, and most days I'm pretty good at keeping a 1000 cal deficit. That's supposed to correspond with burning 2 lbs per week, which came out *exactly* right for the first three months. Then christmas happened, oh well, back on track in Jan. However, now, if I want to keep things moving with the weight loss, it seems like I need almost a 1500 cal defecit, and that's still only getting me a pound per week. I'm wondering which of the following seems more likely:

• Is the Fitbit overestimating cal burned? It ranges from 2500 if I sit on my butt all day to 4300 on the days that I barely ever sit down.  
• I've had more of those 4000-ish cal burned days in the last few months. Maybe it overestimates more when there's higher activity?
• Has my metabolism slowed down in a way that isn't captured by the HR monitor etc? I do try to do a day each week where I eat at maintenance, just to keep the body happy. And, I'm nowhere near the kinds of low body fat levels that trigger your metabolism's emegency response. I still have plenty of surplus body fat! 🙂

I'm fairly certain the calories-in numbers are, and have remained, accurate. I'm pretty detailed about measuring and recording food. 

Maybe I shouldn't be so closely matching in to out? Eg if Fitbit says I'm way below target on cal in, maybe I should just let it be, rather than eating just to catch up? 

Thanks for your time and assistance!

Cheers,

Jeff

[J3ff]

I should add, I recognize that pounds don't drop at a steady rate, and water plays a factor; it's definitely true that my weight will hold steady and then have sudden drops, which is common. When I say 2 lbs/wk or 1 lb/wk, I'm talking about month to month averages.

I weigh myself each morning at exactly the same time, before breakfast, and only look at the long-term averages, eg the 3 month weekly average window in the Fitbit app.

[Dominique]

@J3ff: I think the main factor in your case is the metabolic adaptation that took place as you lost a bunch of weight in a short period of time. AFAIK, Fitbit has no way to take this into account: it uses the standard Mifflin St Jeor equation (or something very similar) for your BMR, which means gender, age, height and weight. Your energy expenditure is based on your BMR. As a result of metabolic adaptation, your actual BMR may be significantly lower than the calculated one based on age etc.

As to the margin of error due to the tracker itself: several people have reported HR-based Fitbits tend to overestimate calories burned.

Despite all that, calories in vs. calories out is still valid, though you may need to make adjustments to the numbers based on your observations, which you appear to be doing.

Congrats for your weight loss in any case!

[Dominique · Accepted solution]

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@J3ff wrote:

I recognize that pounds don't drop at a steady rate

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Yes, weight loss usually isn’t perfectly linear. Just in case, since you appear to be new here: have you heard about TrendWeight? It’s a free web-based service you can link your Fitbit account to. It’s often mentioned on this forum and used by several contributors (I love it). If you’re not familiar with it, give it a try.

[J3ff]

Thanks, TrendWeight is cool!  It says I've effectively been running a 750 cal deficit based on the weight loss, and on the Fitbit app my deficit averages a little over 1000. So, out of ~3500 cal/d Fitbit is only overestimating total cals burned by 9% or so. Okay, this is good to know! Thanks!

[Dominique]

I would say a 9% discrepancy is very good. In your case it means a calculated deficit won’t become an actual surplus. Which Fitbit model are you using?

TrendWeight is especially useful when your daily weigh-ins (if you are weighing yourself daily) are all over the place and it’s hard to see where you’re headed.

[J3ff]

Totally, thanks Dominique! I'm using the Charge 2, which has a heart rate monitor (not sure how big an effect the HR data have on the Fitbit's accuracy, but I assume it hopefully helps?). This over estimation info will be critical, as well, when I decide to switch to maintenance... 10% excess calorie intake could sneak up on me quickly!