The colon is a digestive organ!

We read the recent “Staying Current” article concerning the digestion and absorption of major nutrients by Goodman (2) with great interest and some disappointment. Although we agree with the author that common textbooks tend to gloss over the details, we are far more concerned about the tendency to ignore the digestive role of the colon (5). Considerable amounts (10 –15%) of dietary carbohydrates are digested and absorbed within the large bowel (3). Colonic fermentation of malabsorbed carbohydrates should thus be acknowledged as an integrated part of the normal digestive process–a physiological phenomenon–rather than being conveyed merely as a pathological consequence of certain enzyme deficiencies [e.g., lack of lactase or trehalase or Na -glucose transporter 1 (SGLT1) mutations (2)]. Furthermore, Goodman states that short-chain fatty acids (SCFAs) “ . . . result from the digestion of fats by the bacteria in the colon and thus often contribute to diarrhea by providing an osmotic gradient” (2). This is not correct: SCFAs result from the colonic fermentation of carbohydrates and prevent diarrhea by reducing the osmotic effect of unabsorbed carbohydrate molecules and facilitating the uptake of electrolytes and water (1). Unfortunately, the colon seems to be a continuous source of misconceptions (4).