Direct Measurement of Microstructure of Ingestive Behaviour After Initiation of GLP-1 Receptor Agonist Treatment at Maximum Dose (DIGRAT)

Direct Measurement of Changes in Food Selection and Intake Behaviour After Using the Maximum Dose of GLP-1 Receptor Agonists

Ingestion of food instigates the release of a battery of enteroendocrine peptide hormones that help control gut motility and digestive secretion. Peptide hormone products of the enteroendocrine L-cell and GLP-1 in particular, play multiple roles in relation to the regulation of pancreatic islet function and gastric emptying and the induction of satiety pathways in the central nervous system The mechanism of action of GLP-1 RAs on food intake reduction is mainly mediated through both peripheral and central nervous system (CNS) pathways. GLP-1 RAs directly stimulates POMC neurons and inhibits neuropeptide-Y (NPY) and Agouti-related peptide (AgRP) neurons in the arcuate nucleus resulting in a reduction in hunger and increases in fullness4.

While there were studies which indirectly measured the changes of food preference and eating behaviour in humans after using GLP-1 RAs via visual analogue scales (VAS) or Patient's Experiences Questionnaires the investigators found there is a necessity to conduct the studies to do direct measurements of the changes of food preference and eating behaviour. Direct measures of an altered food selection in humans after using GLP-1 RAs have virtually not been performed likely due to the significant methodological and conceptual challenges they pose to researchers and study design. However, direct measures represent an essential component in the attempt to understand how GLP-1 RAs alters eating and diet selection which is the main reason of conducting this study. This innovative experiment will be a critical and a novel test of the explicit experience of humans with high-sugar high-fat fluids after using GLP-1 RAs and its potential role for the understanding of possible mechanisms determining post-treatment outcome such as weight loss.

Food intake results in the feeling of fullness, but different foods with the same energy value may induce a variable amount of fullness. Many of the satiety signals come from the lower part of the small intestine where satiety hormones are released.

Obesity is associated with impaired metabolic pathways along with disordered signalling of appetite, hence individuals with obesity experience symptoms that manifest as an increase in hunger and lack of fullness. Thus, using analogues of our natural satiety/fullness hormones in individuals with obesity can suppress excessive hunger and increase fullness via slowing down gastric emptying, increasing secretion of insulin and satiety hormones and affecting on Brain-Gut axis which leads to less calorie intake and weight loss.

In this study, the investigators want to review the changes in the microstructure of ingestive behaviour of participants after using the maximum dose of an obesity management medication which is similar to our natural satiety hormone via a specific device named drinkometer allowing real-time measurement of subjects' intake rate and total volume intake of one standardised liquid meal. The drinkometer device consists of an electronic scale on which a container with the liquid meal is set at each study visit in the Clinical Research Centre of St. Vincent's University Hospital. Guidance, fixed to a casing around the balance container system, delivers a tube close to the bottom of the container. The other end of the opaque tube extends to the subject and allows the sampling of the liquid meal via a mouthpiece. The tube, mouthpiece and liquid container are biocompatible and food safe. The participants will attend five visits in total including 1) Pre-Intervention site visit, 2) 4 weeks after initiation of the treatment, 3) at 12 weeks, when maximum dose is reached, 4) 26 weeks after initiation, still at maximum dose, 5) 52 weeks after initiation, still at maximum dose.

The primary objective of the study is to use an analysis of ingestive behaviour to test the hypothesis that using a maximum dose of a GLP-1 receptor agonist medication changes the microstructure of the ingestive behaviour with specific patterns that can be used for behavioural phenotyping and therefore, treatment decision and prediction of the clinical outcomes.

Inclusion Criteria:

• Age 18 to 75

  • Treatment Group: BMI > 30 kg/m2 and clinically indicated for GLP-1 RA's treatment.
  • Controls with obesity (BMI ≥ 30 kg/m2) with no history of GLP-1 RA's treatment.
  • Healthy normal weight controls (BMI < 25 kg/m2) with no history of using GLP-1 RAs

• Independently mobile

• Capacity to consent to participate

Exclusion Criteria:

• Pre-treatment factors impairing the ability to consume meal such as Significant dysphagia

  • Gastric outlet obstruction
  • Systemic or gastrointestinal condition which may affect food intake or preference
  • Pregnancy or lactation (At the beginning of each study visit, a urine pregnancy test will be performed for all female participants).
  • Active and significant psychiatric illness including substance misuse
  • Significant cognitive or communication issues
  • Medications with documented effects on food intake or food preference
  • History of significant food allergy and certain dietary restrictions (except for lactose intolerance)