This is a quite possible scenario - calories available change based on how much you move and using an activity tracker is the best way to accurately estimate and adjust available calories, to make sure you eat less than you spend and thus you lose weight. Please read on!
We will use Fitbit as an example, but this is applicable to any wearable activity tracker.
1. When Fitbit is not available or not used, MyNetDiary or PlateAI estimate your typical daily calorie expenditures per "Sedentary" activity level, which includes some typical daily chores, walking, etc. The estimate depends on your current weight, height, age, and gender. For example, your estimated daily calorie expenditures on "Sedentary" level could be 2,500. MyNetDiary and PlateAI do not have any other information about your activities, so this is the best estimate available.
2. On any given day, depending on how much you move and exercise, your actual calorie expenditures will be different that the estimated (2,500 in this example). It could be 1,700 calories, could be 2,500, or 3,000 and so on. A wearable activity tracker is meant to calculate and register your accurate calorie expenditure, whether it is lower or higher than the estimate.
3. If you were active and did exercise, you can easily spend more that the typical estimated "sedentary" calories, e.g. spend 3,000 calories, so when you sync your Fitbit and this information arrives to MyNetDiary, your available calories will be increased by 500 (that is 3,000 - 2,500 estimate).
4. BUT, if were not active on this day and barely walked around, Fitbit may calculate your actual daily expenditures as e.g. 2,150, which is 350 calories fewer than the 2,500 calories estimate. In this case, when you sync your Fitbit and this information arrives to MyNetDiary or PlateAI, your available calories will be decreased by 350 (that is 2,500 - 2,150).
Continuing this example, if you estimate was 2,500 calories and were planning to lose 1lb/week (that is losing 3,500 calories/week or 500 calories per day), our app should have calculated your food budget being 2,000 calories/day. If you spent 2,150 calories and ate the planned 2,000 calories, you calorie deficit for the day is 150 calories. You are still losing weight, but not as fast as planned. If you weren't using an activity tracker you'd be unaware that your calorie deficit is less than planned, that you need to be more active, or you need to eat a bit less if you are not active. Fitbit, reducing available calories helps you to know exactly where you stand and keeps your weight loss on track.