It's not easy but certainly possible. For a reasonably tall male (higher calorie burn), being active (>15k steps a day) while eating around 1500 calories a day

It's not easy but certainly possible. For a reasonably tall male (higher calorie burn), being active (>15k steps a day) while eating around 1500 calories a day will lead to a deficit of up to 15,000 calories a week. Eating 1,500 calories per day is restricting but not starving, and burning 3,500 calories per day is a very active lifestyle but not some extreme sports or so. But as others have noted, it often doesn't seem to be sustainable as your body will react to that kind of calorie deficit.