Except it isn’t really 4g per day in a vacuum. As you gain weight every kg needs an additional ~20 calories per day to sustain its basic processes. So by year 20 you are eating an extra 600 calories per day to sustain that weight plus an extra 4g (~36 calories) to continue to gain weight which is a quite noticeable amount of food.

At this point cutting the equivalent of 50+ oz of coke or a little more than a Big Mac per day would leave you feeling hungry, but that food slowly crept in over time.