My girlfriend is very fit, gym everyday, but she is losing weight and for many years she has noted that every time she eats food seems to pass straight through (almost immediate). She eats healthy for sure and eats very regularly, maybe five times per day (plenty of fruit). I begin to worry about her weight loss because, whilst she is very (very) fit, she cannot afford to lose more weight (she is lean but also suffers on long plane or car journey with joint pain in the butt, no meat to sit on so as to speak). What should we do (?)