• Tomohiro Kagawa, Erika Mori, and Ippei Yamaoka.
• Medical Foods Research Institute, OS-1 Division, Otsuka Pharmaceutical Factory, Inc., Tokushima, Japan.
• Nutrition. 2023 Dec 1; 116: 112162112162.

ObjectivesThe aims of this study were to evaluate gastrointestinal (GI) retention of an ingested meal by fluorescence imaging and compare how retention is affected by differences in the physical characteristics of meals.MethodsMice were given an oral fluorescent indocyanine green (ICG) probe enclosed in a liposome. We evaluated the correlation between abdominal and GI fluorescence signals. ICG was administered to mice treated with atropine, and abdominal fluorescence was observed repeatedly. Mice were continuously given a regular chow or a liquid diet containing a low or high methoxyl (LM or HM)-pectin through a catheter placed in the stomach for 2 d, after which the mice were given ICG. In all studies, the mice's abdominal and GI fluorescence signals were observed with in vivo imaging equipment.ResultsThe fluorescence intensities (FIs) of the abdomen and the excised GI tract correlated strongly. Attenuation of the abdominal FI was delayed in the atropine-treatment group compared with the non-treated group. The attenuation of abdominal FI 8 to 24 h after ICG administration was significantly weakened in the HM group compared with the regular chow and LM groups.ConclusionsObserving FI attenuation around the abdomen allows for the evaluation of GI tract retention of an ingested meal. Compared with a solid meal, a liquid meal stays longer in the digestive tract, whereas a liquid meal in which the viscosity increases in the stomach is retained like a solid meal.Copyright © 2023 Elsevier Inc. All rights reserved.

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