Discussion
The purpose of this study was to investigate in healthy participants whether acute exposure to an NGTF that forms an intragastric gel results in different gastrointestinal responses compared with a non-gelling feed. Using MRI, we demonstrated with the alginate-containing feed an intragastric appearance consistent with gelling, which previously has been shown only in animal studiesGCV reduced more rapidly after F + ALG and individual GCV responses appeared less varied. The gut peptides GLP-1, GIP and PYY, which slow gastric emptyingThe similar levels of circulating glucose and serum insulin with the two feeds, in contrast to the blunted incretins GIP and GLP-1 with F + ALG, would refute a marked difference in the rate of delivery of at least glucose, to the small intestine. Similarly, no difference was seen in blood glucose profile when an alginate-containing drink was consumed orallyAlternatively, alginate reaching the small intestine may mask nutrient sensing if the gelling fibres interact with the intestinal mucus layerWe believe this study is the first to identify a difference in SBWC with an alginate-containing NGTF compared with a non-gelling feed. The initial reduction, below baseline with both feeds, in SBWC was comparable to other studies, including a comparison of bolus and continuous tube feedingThe subsequent progressive increase in SBWC, with both feeds, has been attributed to pancreato-biliary and enterocyte secretions in the ‘intestinal phase’ combined with greater movement of mobile water from the stomachThe relatively small volume of feed given may have reduced the effect on appetite in contrast to other studiesCompliance with the upper gastrointestinal symptom scores recording and completion of the fecal charts, and fecal sample collection was high and gave no evidence of changed or abnormal bowel habits or symptoms with either feed. This may reflect the young, healthy nature of the participants and the small amount of feed provided.The feeds had comparable energy, macronutrients, osmolarity and fibre content. The different fibre sources, however, may have confounded our interpretation of the results. The Scientific Advisory Committee on Nutrition (SACN, 2015) defines dietary fibre as including all carbohydrates that are neither digested nor absorbed in the small intestine and which have a degree of polymerisation of three or more monomeric units, plus ligninWe acknowledge that GCV is a proxy for gastric emptying, as it includes gastric secretions and rate of delivery of feed into the stomach (the latter identical in the two feeds in this study by design) as well as passage of gastric contents out of the stomach. Differences in gastric secretions are thought to be unlikely between the two feeds as the energy and macronutrient content were the same and delivery volume is considered to be more important than content with respect to gastric responsesDifficulties with cannulation resulted in a smaller sample than intended for the blood-based measurements. This may have resulted in an increased risk of type 2 errors. In future studies, more participants should be recruited in anticipation of this issue.