I don't think it's 800 grams period. I'm not up on fibrous carb contents of foods, but is it even possible to eat several hundred grams a day?
How much broccoli would you need to eat to equal 100 grams of carbs?
Like Flex Wheeler claimed to need to up his calories to 6000-8000 when dieting because his metabolism is so fast. Bullshit. 
my total carb intake is about 280g a day, my total starches being 90 or so, so the rest comes from the 26oz of broccoli and 12 cups of spinach a day im eating. im eating a shit tonne of fats to.
so, i guess if he ate 10oz broccoli over 5-6 meals along side 3 cups spinach per meal, he'd be about 400g fiberous? i dunno. thats what the guy i have doing my prep tells me. maybe his #'s are off.
but like you 800 grams of carb a day and he looks that flat? thats 3200 cals from carbs alone
either hes exaggerating, or needs to cut back on the cytomel.