Your employer presumably still needs someone to do work. If you quit they will raise the wage they offer until they can hire a new employee. The basic income gives power over employment to the employees instead of the employers. You will be tempted to work once the wage and benefits offered meets your demands.

I used to think I was "special", that I could eat whatever and that I wouldn't gain weight because my body just regulated itself well. Then, just for fun I decided to count calories for a month and found that I ate almost exactly the recommended daily average for me (6', 30 yo guy, 5 hours of running a week, ~= 2600 Calories).

Try counting calories. Don't diet, just check on what you actually eat. I'll bet it's a lot closer to the recommended amount than you imagine it is.