IT is well known that fat is well absorbed by man when consumed in amounts of 50-150 gm. per day. Under,,these conditions, the apparent absorption of fat (I - F/I X 100, where I is intake of fat and F the Amount excreted in the faeces) is more than 90 pef'cent, less than this proportion being considered pathological. When the intake of fat is relatively low, however, the apparent percentage absorption is greatly reduced (58-62 per cent)1,2. The purpose of this communication is to provide evidence that the fat which is excreted in the fæces, and which is assumed to be unabsorbed fat in calculating the apparent absorption, is mainly of non-dietary origin, and that the true absorption of fat is not necessarily lower when the intake of fat is reduced. The evidence, which is based on the study of diets of different fat and crude fibre contents, also indicates that the additional amount of fat which is excreted in the fseces when the fibre content of a diet is greatly increased3 is not unabsorbed fat, but is probably wholly of endogenous origin.
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Walker, A. Effect of Low Fat Intakes and of Crude Fibre on the Absorption of Fat. Nature 164, 825–827 (1949). https://doi.org/10.1038/164825a0