I do 3 days fasts almost every week and have an office job. it is absolutely doable and it is even easier than when you are staying at home (because you are distracted by work + colleagues). So you can do it 😉 good luck.
I find it easier to fast when I’m busy and distracted at work. If you aren’t doing a physical job, why do you need to have juice or smoothies? That’s not fasting. Juice is bullshit anyway. Eat your veggies and drink water. If you want to fast at work, just do it. You don’t need food to sit at a computer.
If I’m just doing a very low calorie day I use vitality proteins with collagen it’s 70 kcals a scoop 18g protein and biotin. I also take my multi. You can just throw the powder in your coffee or a smoothie