> I will certainly not measure the weight of a banana I eat, and anything else is just a very rough estimate as a banana can be twice the size of another banana

> I will certainly not measure the weight of a banana I eat, and anything else is just a very rough estimate as a banana can be twice the size of another banana. This is the wrong way to look at it. Sometimes you'll have a larger banana, sometimes a smaller banana, but overall it'll average out. What you need is consistency to compare to your own previous measurements, not perfect accuracy. For example: By counting my calories and keeping track of my weight, I've learned that I burn about 2200 calories per day. If I went over my foods and measured them perfectly it probably wouldn't be that number, but because I'm consistent in how I measure it I can know with certainty whether I'm above or below that limit. I've been able to reliably control my weight for a few years now because of this and I'm not even measuring, just eyeballing how much of things I use.