Materials and methods

This exploratory study was conducted with prior approval from the ethics committee of the University of Duisburg-Essen (reference number 23-11570-BO). Written informed consent was obtained from all participants before the start of the trial. To obviate the use of ionizing radiation, gastric emptying was assessed with MRI. MRI, which has been validated against the gold standard of scintigraphy [13], allows for repeated non-invasive measurements of gastric content volumes without exposing participants to radiation.

Subjects

A total of 16 healthy participants were considered eligible for inclusion. Each participant completed a medical history questionnaire to identify potential exclusion criteria in advance. These included conditions that might declare participants unsuitable for MRI-scans or health factors that could influence gastric emptying time (see exclusion criteria, Table 1).

Inclusion criteria | Exclusion criteria
• Healthy individuals aged ≥ 18 years | • Pregnancy
• At least 12 h of fasting (no food or fluids) before the beginning of the study | • Pre-existing gastrointestinal diseases (e.g., Crohn’s disease, reflux disease)
 | • Conditions affecting gastric motility (e.g., diabetes mellitus)
 | • History of abdominal surgery
 | • Medications influencing gastrointestinal motility
 | • Claustrophobia
 | • Known food allergies, intolerances, or vegetarianism, veganism

A total of 241 MRI-scans were carried out between August 2024 and January 2025. 15 participants were initially assumed eligible to participate. However, one participant had to withdraw from the study because of time issues and was later replaced to reach the intended total of 15 healthy participants (6 females and 9 males), who completed all three test days. One participant had to repeat a study day due to the onset of a migraine during the study. The 15 participants were aged between 22 and 29 years (mean 26.1 ± 2.0 years) and mean BMI was 22.55 ± 2.80 kg/m². For characteristics of the study population, see Table 2.

Characteristics
Sex | 
Female | 6 (40%)
Male | 9 (60%)
Age (in years) | 26.1 ± 2.0
Height (in cm) | 177.2 ± 11.4
Weight (in kg) | 70.7 ± 9.6
BMI (kg/m²) | 22.55 ± 2.80

Study protocol

Each participant consumed three different meals on three separate days, with gastric filling assessed using MRI.

The three standard meals varied in macronutrient composition (high-protein, high-fat and high-carbohydrate) and were selected based on common dietary patterns:

Vegetarian rice dish: Chop suey with rice (high-carbohydrate)Currywurst (bratwurst topped with curry-flavored ketchup) with French fries and mayonnaise or ketchup (high-fat)Half a chicken (roast chicken) with salad and curry ketchup (high-protein)

Meals in this study were considered high of its respective macronutrient, when exceeding the acceptable macronutrient distribution ranges of daily caloric intake [14], which is > 35% of total energy from fats (approx. 9 kcal/g), > 65% from carbohydrates (approx. 4 kcal/g) and > 35% from proteins (approx. 4 kcal/g).

To collect data on the standard meals, three test meals of each meal type were used as „reference meals“, the main components were weighed, and their caloric content and macronutrient composition (carbohydrates, fats, proteins) were calculated using nutritional value tables [15] (What’s In The Foods You Eat Search Tool, 2021–2023, Based on the Food and Nutrient Database for Dietary Studies 2021–2023 (FNDDS) [16](Table 3). All meals were ordered from the same restaurants to provide comparable compositions of ingredients and to represent typical portion sizes. Many high-protein diets are rich in fat, too [17]. The selected high-protein meal also meets the criteria for a high-fat meal but is referred to as high-protein due to its major component.

Meal | Composition | Fat (g)kcal (%) | Carbohydrate (g) kcal (%) | Protein (g) kcal (%) | Total energy content (kcal) | Weight (g) | Volume at t0 (ml)
High-fat | Currywurst + french fries + ketchup | 69.3 ± 3.0 (51.5%) | 122.3 ± 8.5 (40.5%) | 24.3 ± 1.5 (8%) | 1212.4 ± 29.8 | 454.0 ± 13.9 | 718.55 ± 48.1
Currywurst + french fries + mayonnaise | 85.9 ± 3.0 (57.5%) | 118.4 ± 8.5 (35,2%) | 24.3 ± 1.5 (7.2%) | 1344.2 ± 29.8 | 454.0 ± 13.9
High-carbohydrate | Chop suey + rice | 7.5 ± 1.0 (15.2%) | 82,7 ± 4,6 (75.1%) | 10.7 ± 0.9 (9.7%) | 440.9 ± 30.5 | 682.3 ± 63.0 | 835.30 ± 95.9
High-protein | Roast chicken + salad + curry ketchup + dressing | 47.5 ± 1.6 (58.9%) | 8.4 ± 0.3 (4.6%) | 66.0 ± 3.2 (36.4%) | 725.7 ± 26.2 | 602.3 ± 36.0 | 770.01 ± 99.0

Participants consumed the meals on an empty stomach (at least 12 h of fasting; water was allowed up to one hour before the beginning of the study) within 20 min. Each meal was accompanied by 200 ml of water. After the meal, no additional food or liquid intake was planned, although still water was provided ad libitum in 200 ml portions, with consumption recorded accordingly (Supplementary Table 1).

Between the scans, the participants were allowed to sit or walk to mimic the movement of a usual day, but no athletic activity was permitted.

To quantify gastric filling, an initial MRI scan was performed in the fasting state (t-20). Following MRI scans were carried out immediately after meal consumption and then at two-hour intervals, up to a maximum of ten hours after eating. If complete gastric emptying occurred before ten hours had passed, no further scans were performed. Complete gastric emptying was defined as the gastric content volume at the fasting state (t-20) ± 10% of the initial volume at t0, to account for possible water intake during the study.

MRI technique

All MRI-scans were conducted in the same MRI-scanner (SIEMENS MAGNETOM 1.5T, Siemens Healthineers, Forchheim, Germany) in the Institute for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Germany. All scans followed the same protocol of 7 sequences (Table 4). The participants were positioned supine with a radiofrequency coil placed around their abdomen.

Every MRI-scan took about 10 min including intervals of end-inspiratory breath holds to minimize motions artefacts.

The application of contrast medium was not necessary for the MRI examination because the solid meal gave sufficient contrast for volume measurement.

Sequence | Orientation | Slice thickness (mm) | Echo Time (TE) (ms) | Repetition Time (TR) (ms) | Field of view (mm) | FoV Phase (%) | Matrix | Flip angle
Localizer | Transversal | 6.0 | 2.45 | 5.6 | 430 | 100 | 256 × 179 | 20°
T2_TRUFI_n_cor_6mm | Coronal | 6.0 | 1.85 | 3.7 | 380 | 90.6 | 256 × 230 | 54°
T1_Vibe_s_dixon_cor_3mm | Coronal | 3.0 | (1) 2.39(2) 4.77 | 6.7 | 400 | 100 | 288 × 259 | 10°
T2_HASTE_n_cor_6mm | Coronal | 6.0 | 91.00 | 1200.0 | 380 | 84.4 | 256 × 256 | 180°
T1_Vibe_n_dixon_tra_3mm | Transversal | 3.0 | (1) 2.39(2) 4.77 | 6.7 | 380 | 81.3 | 320 × 240 | 10°
T2_TRUFI_n_tra_6mm | Transversal | 6.0 | 1.85 | 3.7 | 380 | 90.6 | 256 × 230 | 54°
T2_HASTE_n_tra_6mm | Transversal | 6.0 | 104.00 | 1000.0 | 380 | 71.9 | 256 × 205 | 160°

Measurement of gastric content volume

Gastric content was identified by a clear contrast to the surrounding tissues in the transversal plane of the TRUFI-Sequence. This sequence showed the least motion artefacts while providing sufficient contrast between gastric content and the surrounding tissues and was therefore used for volume determination. Segmentation of the gastric content was performed manually on each slice to calculate the total gastric content volume using syngo.via (Siemens Healthineers, Forchheim, Germany) (Fig. 1). If the gastric area was not completely imaged in the axial plane of the TRUFI-sequence, the coronal plane of the TRUFI-sequence was used for volume determination.

Fig. 1: Gastric content assessment by MRI in the axial plane of the TRUFI-sequence. Shown is the gastric content after consumption of the high-fat meal. Even without contrast medium, gastric content shows sufficient contrast for volume determination. MRI-scan (a) after 12 h of fasting, (b) directly after meal consumption, (c) after 120 min, (d) after 240 min, (e) after 360 min

Data analysis and statistical analysis

Statistical analysis was performed using the software SPSS Statistics Version 29.0 (IBM, Armonk, USA) and Excel (Microsoft 365 Subscription, Microsoft Corporation, USA).

To compare gastric emptying times, gastric half-emptying times (t₅₀) were calculated via linear interpolation and expressed as means with standard deviations. The t50-value indicates the time needed for the initial postprandial gastric content volume to decrease by 50%. The Shapiro-Wilk-Test and Q-Q-plots were used to test the data for normal distribution. Possible group differences between meals were assessed using a mixed-design analysis of variance (Mixed ANOVA) with meal type as a within-subjects factor and sex as a between-subjects factor. Significance level was set at α = 0.05. Post-hoc pairwise comparisons within the Mixed ANOVA were Bonferroni-adjusted.

Additionally, t-tests were used to determine possible differences between male and female participants within each meal type. Because of multiple testing, a Bonferroni correction was applied as well, resulting in an adjusted significance threshold of α = 0.017 (0.05/3).

All statistical analyses and results were verified by the Institute for Medical Informatics, Biometry and Epidemiology of the University Hospital Essen (IMIBE University Hospital Essen).