Can a fitness tracker have a negative effect?

From experience, trackers do not just give you calories, you have to work for them. Depending on your settings and activity level you might not get hardly any adjustment unless you bust your tail. Bottom line, if you like what you are doing and it works, do not try to change it.

I don't let my Vivofit change my MFP calories. I do add running data from my Garmin watch to MFP. Just use your Fitbit or Vivofit to encourage you to hit a daily steps target.

I guess Person1 hasn't been using MFP how it is intended because Person 1s are supposed to eat back their exercise calories.
Trackers just make those measurements more accurate (in theory).

I see your point and I do think if you didn't eat back 'ordinary activity' calories before (and who does) but now your Fitbit is adding calories for it, you'll probably eat more with it. I did.

But in your example it was 'workout calories'. And the assumption seemed to be that the Fitbit calced them higher than the person. I don't know how common that is, given how many posts I see about MFP's database exaggerating exercise calories.

Your hypothetical seems to be that Fitbit would add calories beyond what allows for weight loss. IME, Fitbit is pretty spot on at estimating my maintenance calories, and thus that doesn't seem to happen.

When I first started I had a Fitbit, but it didn't cross my mind to eat back the calories, even though I saw them. I was more focused on eating a particular way and meeting my MFP calories (which I did not yet quite understand included exercise legitimately, rather than "maybe if you want to and are hungry"). I also lost at a higher rate than MFP predicted, because I'd said I was sedentary and I was not. Eventually I gathered the connection between Fitbit calories and activity level and started eating back some of them, and now I use the Fitbit more to keep me honest about my activity level (I try to be active, but I have negative adjustments when I'm not). Anyway, so arguably I did eat more with the Fitbit than without it when I recognized that the calories it was adding were connected to something real--that I was at least lightly active--but had that not been the case, had I been losing only what MFP said I should, I would have continued to ignore the Fitbit calories, I'm sure. So I'd say the effect of Fitbit was to make me use MFP properly, by correctly estimating my activity level or otherwise accounting for it (which you are already supposed to do with MFP, but many people just assume sedentary).

The bigger effect of Fitbit for me is motivating me to be more active in my daily life, so that I actually was lightly active and am often active vs. sedentary or close to it, even apart from intentional exercise.

I personally would adjust if I weren't losing weight, though, and based on the discussions I've seen here and on my friends' feed, I don't think that's uncommon at all.

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If person 1 has set their activity level to include their exercise then they shouldn't link their fitness tracker with MFP.

If person 1 logs their exercise on MFP then again they shouldn't link their fitness tracker with MFP.

If person 1 logs their exercise on their tracker's website for anything other than walking and has MFP set as sedentary then they should eat back those calories.

If person 1 is doing TDEE-x% then they should use the data from their fitness tarcker to calculate an average of their TDEE and then custome set their MFP goal to that value - their required deficit and not link their accounts or eat back their calories as those caloreis are already included in their goal value.

BTW I do the last one of these and it works best for me as I track a rolling average of my TDEE and adjust my MFP goal if necessary.

I guess Person1 hasn't been using MFP how it is intended because Person 1s are supposed to eat back their exercise calories.
Trackers just make those measurements more accurate (in theory).

Yes, in the first scenario, Person 1 has likely been undereating.

I've been using a fitbit and I just don't eat back my calories. Seems to work for me. Just nice to know that I am staying active during my workday and to challenge myself to move as much as possible! Also tells me that I am in fact getting into a cardio range while doing my planned weekly exercise. There is always going to be people that abuse the system and see it as a way to eat more. But I'm not worried about them I am only accountable for myself!

Jesus, I love the hypothetical "Person Number 1." Really. Seriously, though, the more negative effect it had on me was psychological. Tracking my calories became pathological, as I became obsessed with the caloric count of every single thing I ate (read: obsessed). The more obsessed I became, the more I would have a tendency to overeat because I would get bitter about my relationship with tracking (counterintuitive, I know). That contribution doesn't really help with your question, but I do think it can be negative in that way.

:laugh: Very good point!

I had the opposite with my jawbone up. It wasn't giving me enough calories and I ended up getting sick from not eating enough for the activity level I was doing.

I went back to the TDEE method and I have an app on my phone that tracks steps to make sure I move enough at work.

I have a Bodymedia fit. When I follow its recommendations I gain weight. Basically it reads about 30% higher than my actual burn (I have verified this number by tracking my actual intake, bodymedia's numbers, and my weight very carefully for the past 15 months. )

So, I was taking a 15 % cut to lose. But the bodymedia's overestimating my TDEE by 30% meant that when I used these numbers, I was actually eating at a surplus. Thus I gained 10 lbs over the15 months. I kept thinking my body would "reset" and it would actually work. Every online calculator I consulted indicated I was overeating, but still I believed. . .

Let me show you the numbers:

My actual (verified by results) TDEE: about 1650 (some days more some less, as activity varies)
Bodymedia TDEE estimate: 2350 (average)
Total daily eating goal per 15% off Bodymedia TDEE: 1997

So when I was eating 1997 cals a day, I thought I was eating at a nice 350 calorie deficit. In reality I was eating at 350 calorie SURPLUS!! Thus the weight gain. It would have been more, but many days I ate less than 1997 because it just felt like too much.

I now know that my actual TDEE is basically 70% of what the Bodymedia reports. (1650/2350=70%)

I have unlinked the Bodymedia from MFP and I now use that 70% number as a guideline. I subtract about 250 to create a deficit. It turns out that it is about what 1200 + exercise is for me. I lose just over 0.5 pounds per week with that, which is very close to what MFP predicts for me. When I go back to maintenance I will use 1200+250+exercise to figure my TDEE. That should put me pretty close to the 70% Bodymedia number.

So, if the Bodymedia is reading accurately for you, it should work with MFP. But if it is off for you,it will mess up your MFP number, unless you manually enter a different goal number into MFP.

I would use activity trackers carefully and verify with results.

My theory is that the farther you are from the averages that are used to generate height, weight, and calorie burning formulas, the farther off the activity tracker will be. I am definitely below the average person's height and weight and so I would not fit the norms. Of course after gaining weight, I was almost back there!

Unfortunately when I contacted Bodymedia, they were unwilling to consider that their product might have a bigger than reasonable margin of error for me. It has been an expensive mistake!

can drinking water have a negative effect? yes, if you drink too much.

can having great sex have a negative effect? yes, if you suffer from sex addiction (or if your spouse finds out about it)

can winning the lotto have a negative effect? yes, if the money drives a wedge between you and the rest of your family.

can the mfp forums have a negative effect? yes, if you start overthinking things by posing questions like the one in this thread.

People need to know that activity trackers are not completely accurate, and that until they are verified with an individual's results, they should be used with caution. Read my post above. Following my Bodymedia resulted in a 10 lb weight gain for me.

Knowledge is power, and the more knowledge people have, the better the outcomes.

Not everyone will have a negative experience with a tracker, but people should know it happens.