Figure 4.

Metabolic fate of oral fructose. When ingesting small doses of fructose (F) and glucose together, as in human nutrition, most absorbed F is converted to glucose, lactic acid and other organic acids within the enterocytes, which appear in the portal vein supplying the liver. The amount of F passing to the liver after small oral doses is negligible. Glucose largely passes the liver and enters the blood circulation to be available to all tissues. Lactate will favorably be converted into liver glycogen. Non-converted lactate will pass on to the blood circulation. After ingesting acute large doses (≥1 g/kg body weight, equivalent to >1 liter of sugar-sweetened beverage/juice), F partly escapes its own slow absorption process and will pass on to the colon, where it may cause osmotic fluid shifts potentially leading to laxation and will be fermented by the microbiota leading to the formation of short-chain fatty acids, mostly acetate, which will be absorbed and pass on to the liver with portal blood. In this situation, the absorbed but non-converted fraction of F will serve as substrate for de novo fatty acids synthesis, along with the acetate coming from the colon. As a result of the above, F enters the circulation only in very small quantities. (Based on data from (12, 48–53)]. Figure based on data from Jang et al. (48) and Zhao et al. (53).