How do you know you need a 1st fill ?

The best way to know is if you talk to your doctor and he says you need one,

If you can be satisfied on a cup or less of food for at least 4 hours, you may not need a fill. If you're hungry often and can't be satisfied on a cup of food, you may need a fill.

It's a combination of things

1) are you losing weight (no, fill might be the key)

2) do you feel satiated between meals for at least 3 hr (if not, fill make be necessary)

3) are you eating large volumes (ideally no more than 1 cup) (if yes, there may be inadequate restriction - fill time)

4) are you having symptoms (frequent regurgitation, acid reflux etc) if so fill is not warranted

Your doc takes all this into account and will advise you on what is appropriate. Also, even if a fill is warranted how much volume is also up for debate.

Remember, everyone is different. I eat about 1 1/2 c for my meal. When losing I only ate twice a day with a couple small snacks. It changed all the time because my NUT said don't eat unless you are hungry. It is hard to determine, but since I didn't feel hungry a lot and mostly ate out of habit, I didn't get fills.