Figure 3. Most Fructose Is Cleared in the Small Intestine.

(A) Schematic of digestive system and location of portal vein.

(B) Oral fructose is processed prior to entering the portal vein. Data show portal vein concentrations of the administered labeled hexose (either U-¹³C-glucose or U-¹³C-fructose, with the other administered in unlabeled form) and associated normalized portal vein AUC_{0–30 min} (N = 4 for labeled glucose and N = 5 for labeled fructose).

(C) Oral fructose forms portal vein glucose. Mice received a mixture of unlabeled glucose and U-¹³C-fructose and the concentration of labeled glucose and fructose in the portal vein was measured.

(D) Intestinal gluconeogenesis from oral fructose scrambles the hexose carbon atoms. Labeling pattern of portal vein glucose in mice receiving 1:1 glucose:fructose with either the glucose or the fructose U-¹³C labeled.

(E and F) In Khk knockout (KO) mice, oral labeled fructose appears in the portal vein as labeled fructose (E) and not labeled glucose (F). Bars indicate labeled portal vein AUC_{0–30 min} of the indicated hexose, normalized to wild-type (WT) mice (N = 5).

(G) Normalized AUC_{0–30 min} for labeled F1P in jejunum and liver from WT and Khk KO mice (N = 5).

Data are means and error bars are ±SE. See also Figure S3.