Results

The high-carbohydrate meal was the biggest meal with an average weight of 682.3 ± 63.0 g and an average volume of 835.30 ± 95.9 ml after meal intake, while the high-fat meal was the meal with the smallest weight and volume (454.0 ± 13.9 g and 718.55 ± 48.1 ml). The high-protein meal sized between (602.3 ± 36.0 g and 770.01 ± 99.0 ml after meal consumption). All volumes measured directly after meal consumption include 200 ml of water that accompanied the meal.

On the other hand, the high-fat meal had the greatest energy content, averaging 1212.4 ± 29.8 kcal when served with ketchup and 1344.2 ± 29.8 kcal when served with mayonnaise. In contrast, the high-carbohydrate meal had the lowest energy content, averaging 440.9 ± 30.5 kcal. The high-protein meal yielded a total energy content of 725.7 ± 26.2 kcal.

Due to the drop out of one participant and one study day being repeated, 232 MRI-scans were included in this study. Gastric content volume could be identified and outlined in all MRI-scans for volume determination. Due to incomplete imaging of the stomach at t0, one volume measurement had to be performed in the coronal plane of the TRUFI sequence instead of the axial plane.

Figure 2 shows the gastric emptying for the 3 different meal types over time and Fig. 3 for each meal type separated for sex

Fig. 2: Box plots showing the gastric content volume over time for each standard meal. Boxes show the inclusive median (solid line) and the interquartile range. The mean value is indicated by a cross. Whiskers indicate the 1.5 interquartile range. Outliers are represented as dots. X-axis: time in min, y-axis: gastric content volume in ml

Fig. 3: Box plots showing the gastric content volume over time for male and female participants for each meal type (a-c). Boxes show the inclusive median (solid line) and the interquartile range. The mean value is indicated by a cross. Whiskers indicate the 1.5 interquartile range. Outliers are represented as dots. X-axis: time in min, y-axis: gastric content volume in ml

Across all meal types, most participants showed total gastric emptying after 6 h (36 of 45 consumed meals). Only one male participant reached the defined threshold for total gastric emptying 4 h after consumption of the high-carbohydrate meal.

In the other 9 cases, total gastric emptying was not achieved within 6 h. 5 of these cases reached total gastric emptying after 8 h (1 high-carbohydrate meal, 4 high-fat meals). In the remaining 4 cases (2 female participants), the study day was terminated early due to signs of physical discomfort and hunger (like headaches and vertigo), although the predefined threshold for complete gastric emptying was not reached. 3 of these early terminations occurred in the same participant whose study day had to be terminated early after each meal, with 18–21% of the initial gastric content volume remaining (15–60 ml above the defined threshold; after 6 h for the high-protein meal and after 8 h for the high-fat and high-carbohydrate meals). The gastric content volume of the other participant even increased between the 6-hour measurement and 8-hour measurement (high-fat meal) due to the consumption of water. The detailed drinking protocol is provided in the Supplementary Table 1.

One male participant had to repeat one study day due to the onset of a migraine during the study which resulted in an early termination of the study day. The participant did not report symptoms until 6 h postprandial, so MRI-scans were performed until early termination. The participant showed delayed gastric emptying and after 6 h gastric content volume increased again from 39.1% to 60.2% of the initial volume directly after meal consumption. In this period, the participant only consumed water, as it was allowed. These results are not included in Figs. 2 and 3.

In general, there was a significantly faster gastric emptying of the high-carbohydrate meal (t₅₀ 132.35 ± 33.38 min) than of the high-fat meal (t₅₀ 187.84 ± 41.17; p < 0.001) and of the high-protein meal (t₅₀ 157.57 ± 37.12; p = 0.010). There was no statistically significant difference between the gastric half-emptying times of the high-fat and the high-protein meal (p = 0.129).

While female participants showed - on average and across all meal types - slower gastric emptying than male participants (Table 5), the differences of the mean t₅₀-times between men and women, only reached significance for the high-protein meal (p = 0.003).

t₅₀ in min
Different groups | High-fat meal | High-carbohydrate meal | High-protein meal
Total (n = 15) | 187.84 ± 41.17 | 132.35 ± 33.38* | 157.57 ± 37.12
Sex |  |  | 
Female (n = 6) | 194.83 ± 32.86 | 152.18 ± 37.72 | 188.87 ± 37.52**
Male (n = 9) | 183.18 ± 47.22 | 119.13 ± 23.85 | 136.70 ± 17.52
BMI (kg/m²) |  |  | 
< 20 (n = 2) | 223.5 ± 38.98 | 176.82 ± 22.04 | 180.07 ± 31.67
> 25 (n = 2) | 187.21 ± 61.79 | 112.21 ± 20.00 | 120.78 ± 8.08

Participants with particularly slow or fast gastric emptying did not necessarily show a trend across the different meal types, which indicates non-systematic reasons for different gastric emptying times.

The interaction between meal type and sex (meal type*sex) was statistically not significant (p = 0.154), indicating that the effect of the meal type on gastric emptying was similar for both female and male.

No underweight participant (BMI < 18.5 kg/m²) was included in this study, but 2 participants had BMIs < 20 kg/m² (one female and one male). They showed slower gastric emptying compared to the average, while overweight participants (BMI > 25 kg/m², n = 2, one female and one male) showed faster gastric emptying (Table 5). However, because of the low case number, these findings are only described case-specifically.