This study investigates the digestion and absorption processes in the human small intestine using a well-balanced liquid test meal. The researchers employed a transintestinal intubation technique to sample intestinal content at various levels, allowing for the analysis of the composition of the intestinal content during digestion and absorption. A reference substance, polyethylene glycol (PEG), was included in the test meal to track its dilution and absorption. The study found that the test meal was delivered from the stomach to the duodenum in small portions over a four-hour period, with the maximum amount passing during the second hour. The absorption of fat, glucose, and protein began in the distal duodenum and was generally completed in the first 50 to 100 cm of the jejunum. The concentration of PEG in the duodenum indicated a three- to fivefold dilution of the test meal. The study also observed that the pH in the duodenum and jejunum remained relatively constant during the digestion period. The results provide valuable insights into the normal digestion and absorption processes in the human small intestine.This study investigates the digestion and absorption processes in the human small intestine using a well-balanced liquid test meal. The researchers employed a transintestinal intubation technique to sample intestinal content at various levels, allowing for the analysis of the composition of the intestinal content during digestion and absorption. A reference substance, polyethylene glycol (PEG), was included in the test meal to track its dilution and absorption. The study found that the test meal was delivered from the stomach to the duodenum in small portions over a four-hour period, with the maximum amount passing during the second hour. The absorption of fat, glucose, and protein began in the distal duodenum and was generally completed in the first 50 to 100 cm of the jejunum. The concentration of PEG in the duodenum indicated a three- to fivefold dilution of the test meal. The study also observed that the pH in the duodenum and jejunum remained relatively constant during the digestion period. The results provide valuable insights into the normal digestion and absorption processes in the human small intestine.