I'm taking the "more fat in stools" number to be that the stool analysis fully "digested" and found the fat in the stools that was bound up in the unchewed "food matrix" aka fiber.
Much more fat was being absorbed from the nuts than was being excreted, as far as I can tell.
Quote from the full review that Darryl posted:
Fecal fat loss because of incomplete mastication of nuts or other factors may result in a loss of available energy. Earlier work has shown that whole nuts are inefficiently absorbed (40). Subjects fed whole peanuts excreted 17% of dietary fat in the stool; only 4–7% of dietary fat was excreted when the rats were fed peanut butter (40). On a well-controlled feeding trial with pecans (19), there was increased excretion of fat in the stools of subjects while on the nut diet (25 g/d) compared with the control diet (6 g/d). This represented 8% and 3%, respectively, of the dietary fat of the pecan and control diets (41). Increased stool fat was also noted on a high almond diet (42), but the increment of percent fat in stools (4%) was less than on the pecan (41) and peanut (40) diets. Nevertheless, the losses of fat in stools of nut eaters combined with the observed food displacement would largely explain the lack of weight gain.
I personally found the bolded part (noted by Darryl in a previous post) to seem rather misleading--as in, implying that nuts cause major fat excretion in the stools--in light of the above quote, which is likely where that sentence was intended to "summarize".
If this is true...
He states that every time we eat nuts, five years are shaved from our life spans.
we should all be dead by now. That's just garbage to sell books.