Gastric content is a key risk factor for aspiration during anesthesia. Although standard fasting times are recommended, various factors-including GLP-1 receptor agonists,-can delay gastric emptying. Gastric ultrasound enables real-time, non-invasive assessment of gastric volume and can help tailor perioperative management. The aim of this study explores the effects of different meal types and physical activity on gastric emptying in healthy individuals.

Pulmonary aspiration of gastric contents is a serious and potentially life-threatening complication of anesthesia. Despite adherence to preoperative fasting guidelines issued by the American Society of Anesthesiologists (ASA), certain medical conditions-such as diabetes mellitus-or medications like GLP-1 receptor agonists may significantly delay gastric emptying beyond standard expectations. This creates a need for individualized assessment of gastric contents prior to anesthesia, especially in patients considered at increased risk.

Gastric ultrasound is a non-invasive, point-of-care technique that allows for real-time assessment of gastric volume and content. It may provide a more reliable indicator of aspiration risk than fasting time alone.

This randomized, prospective study aims to evaluate the effects of different types of meals and physical activity levels on gastric emptying time in healthy adult volunteers, using ultrasound-based measurement of the gastric antrum.

Sixty participants aged 18-40 years will be recruited via registration forms provided by the study team. Each participant will provide written informed consent, including acknowledgment of potential food allergens present in the study meals. The day prior to each session, participants will receive a phone call to remind them of dietary restrictions: no clear liquids for 2 hours, no solid foods for 6 hours, and no fatty meals for 8 hours before the study.

Each participant will take part in two separate sessions, conducted on different days. On both days, the participant will arrive fasting and undergo a baseline gastric ultrasound to confirm an empty stomach. If gastric content is detected, the session will be rescheduled.

Participants will be randomly assigned (via computer-generated allocation) to one of three meal groups: high-fat, dairy-based, or fruit/vegetable. Meals will be standardized in volume and composition within each group. The examiner performing the ultrasound will be blinded to the meal group allocation.

In each session, participants will consume the assigned meal within 10 minutes. Gastric ultrasound measurements will be performed at 15 minutes, 3 hours, and 6 hours post-meal. On one of the days, participants will remain in a resting position between measurements. On the other day, participants will walk at a moderate pace for 30 minutes between each measurement interval (i.e., between 0-3 hours and 3-6 hours post-meal). The order of active vs. resting day will be randomized and counterbalanced across participants.

Ultrasound will be performed in the right lateral decubitus position using a convex transducer (2-8 MHz) with an abdominal preset. The antral cross-sectional area (CSA) will be measured using standard landmarks (aorta, SMA, left lobe of liver), and gastric volume will be estimated using a validated formula:

GV = 27.0 + 14.6 × right lateral CSA (cm²) - 1.28 × age (years).

Inclusion Criteria:

• Age between 18 and 40 years
• Ability and willingness to provide written informed consent
• Agreement to comply with study procedures, including pre-study dietary restrictions
• No history of gastrointestinal disease
• No recent abdominal surgery

Exclusion Criteria:

• Lack of informed consent
• Allergy or intolerance to any of the foods used in the study meals
• Medical conditions known to delay gastric emptying, including:
• Obesity (BMI > 30 kg/m²)
• Diabetes mellitus
• Gastroesophageal reflux disease (GERD)
• Hiatal hernia
• Bowel obstruction
• Tube feeding
• Active gastrointestinal disease
• History of gastrointestinal surgery
• Current pregnancy or breastfeeding
• Use of medications affecting gastric motility (e.g., opioids, anticholinergics, GLP-1 receptor agonists)
• Neuromuscular disorders impairing ability to remain in supine position for 6 hours or to walk for 30 minutes