1200 healthy, wholesome, nutrient, non- garbage-y calories is more than enough for most people to not only survive, but thrive. Not only that, you are keeping to that 1200 calories for only one day, so in actuality, your average for the week is higher. So one day, of 1200 calories doesn't mean that you are eating 1200 calories as a whole.
My calories don't change because of my activity (or non-activity) level. But obviously this has been working out beautifully for you. As long as you're content and satisfied and pleased with your results, I say "don't fix what ain't broken". Of course you can experiment and see what results it nets you and if you are displeased with those results, you can go back.
I urge you to find what works best for YOU, regardless of popular belief, the average, the norm, the etc.. I had to ignore a lot of so called *diet wisdom* to lose the weight and keep it off. We have to discover our own personal *diet wisdom* and apparently you have.
Keep at it. You're doing great.

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