A one day juice fast won't give you any kind of noticeable result physically, and it's not going to do much as means of internal detoxification. The juice itself is obviously great for your health (given that it's either fresh-squeezed or completely pure, not sugary and faux-healthy juice and juice cocktail), but like I said, you won't experience much. 16 and 24 hour intermittent fasting is a great way to introduce your body to fasting, though. You'll just have to build it from there. And it's completely fine - don't listen to people who think you're "starving yourself." Fasting is a natural process and it can actually reap tremendous benefits.