There is protein in fruits and vegetables just not as much as in animal flesh. Most people consume too much protein anyway. As to constipation, a lot of people recommend enemas during fasts.
shareAccording to this the drink 'mean Green' which Phil drank a lot of has 10g of protein per batch and 24g fiber. I don't know if that much fiber would get through the juicer. But if carbs are getting in I'm assuming the proteins would get into the juice too.
http://tracker.dailyburn.com/recipes/fat_sick_mean_green_juice
There's still some fiber left in the juice. I've never been constipated when just juicing for long periods of time.
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