The World Health Organisation (WHO) has deemed being overweight or obese as the fifth leading cause for global deaths, with more than 1.9 billion adults being defined as overweight, and 600 million defined as being obese. Conditions associated with obesity, such as stroke, type 2 diabetes, certain cancers, cardiovascular, fatty liver and airway disease can lead to premature death. Obesity results from an imbalance in energy intake versus expenditure, and fat mass accumulates. Studies have indicated that obese animals have a faster gastric emptying time, a weaker contraction of the duodenum, but a stronger contraction and relaxation of the ileum, with associated changes in gastrointestinal neurohormonal levels. The rate of gastric emptying may have an impact on feelings of satiety and has been implied in the pathogenesis of obesity. Moreover, mesenteric blood flow increases 3-fold following a meal and in a swine experimental model, a reduction in weight gain was seen when blood flow was intentionally limited to the gut using flow-restricting endovascular stenting. The authors concluded that this intervention may play a role in the treatment of obesity where other interventions have failed or are inappropriate; however the role of blood flow to the gut in obese individuals is important to elucidate. We hypothesize that nutrient absorption in obese and healthy weight individuals after a standardized meal is determined by differences in gastric emptying and mesenteric blood flow which give rise to different insulin, glucose and gut hormone responses. These may be contributory mechanisms to the evolution or maintenance of obesity.

The aim of this study is to establish the effects of food ingestion on gastric emptying, gallbladder emptying, small bowel water content and splanchnic blood flow as measured by serial magnetic resonance imaging (MRI) in the context of changes in plasma gastrointestinal hormone secretion in human subjects who are obese or healthy weight. In addition, this pilot study will provide the data necessary to power a larger study investigating methods of dietary manipulation in the treatment of obesity.

Method: In order to normalize the pre-study diet, volunteers will have consumed a standard diet for the 3 days immediately before the study visit, which will be based on foods in their normal diet and will be designed to meet their estimated energy requirements and provide 15% of total daily energy intake as protein, 35% as fat and 50% as carbohydrate. Participants will report at 0800 hours following a fast from midnight and after having abstained from alcohol, nicotine, and caffeine from 1800 hours the day before. On arrival, participants will be given a drink of water (200ml). A retrograde cannula will be inserted into a dorsal foot vein after prior intradermal infiltration of 1% lidocaine, with the foot placed in a magnetic resonance (MR) compatible warming box that we have developed, for arterialized-venous blood sampling. Prior to baseline blood sampling, participants will undergo a magnetic resonance imaging (MRI) scan to determine baseline values for superior mesenteric artery (SMA) blood flow, small bowel water content and gastric fluid and gas volumes. Liver fat, visceral fat and subcutaneous fat volumes will also be assessed at this time. Subsequently, a blood sample will be drawn for analysis of concentrations of hemoglobin, glucose, insulin, glucagon-like peptide 1 (GLP-1), glucagon-like peptide 2 (GLP-2), ghrelin and peptide YY (PYY). Serum osmolality will also be measured and subjective appetite assessed using visual analogue scales. The participants will then be given the test meal (in an upright, seated position) and asked to consume it within 15 minutes. The test meal will be comprised of pasta, cheese and tomato sauce, and provides 13% of total energy (E) from protein, 39%E fat, and 48%E carbohydrate.

Following the test meal (time = 0 minutes), subjective appetite will be measured as before, then participants will be scanned at 30 minute intervals for 4 hours to assess gastric emptying, gastric accommodation, gastric motility and small bowel water content, as well as SMA blood flow. Blood samples will be drawn at 15 minutes, then every half hour until 240 minutes after the test meal, with a final blood sample taken at 300 minutes. Subjective appetite will be assessed every hour over the 300 minute study.