I can confirm that a strict fruitarian diet can certainly lead to low protein levels... as a strict fruitarian for a
number of years (2 - 3 I estimate, but actually 5 if i count the time i ate minimal amounts
of salad materials as well...), I had blood tests done at the end
of this time and indeed my protein levels were low... Total protein was at 6.5 when the
ideal is supposedly 7.5... And apart from this, my sports performance as judged by my teachers, was suffering (though I did not feel this in my own body — I was used to performing at that level and felt it as normal for me... and i was newer to the sport than a lot
of them... i had great, better than most endurance... which was very satisfying... but apparently I just did not have the physical
strength that others with less endurance may have had...) something which immediately improved as I added more protein to my diet....