yes this is true.
but you could also be capable of processing certain supplements too.
with adrenal fatigue you are likely to be more allergic to foods/supplements and have lower stomach acid.
but really you should concentrate on your own situation and not worry about other people's responses. adrenal fatigue is very individualized, so once you noticed that the supplements didn't work that should be the end of it instead of trying to fit yourself into someone else's paradigm.
for proteins try cooking them low and slow to make sure they are completely broken down
soak legumes and grains and cook legumes until mushy.
fruits are not hard to digest.
cook vegetables well likewise to break down all the cellulose. or fresh vegetable juices are as easy to digest as fruits.
lots of options
add in indian spices if you like them to enhance digestibility.