Discussion

This exploratory study demonstrates the effect of different meal compositions commonly consumed on gastric emptying times of healthy persons in solid mixed meals. The main results can be summarized as follows: First, the macronutrient composition of a mixed meal significantly influenced the gastric emptying time. Second, on average, female participants showed slower gastric emptying than male participants, however, this difference was only significant with the high-protein meal. Third, total gastric emptying of a commonly consumed meal mostly occurred after 6 to 8 h across all meal types.

Gastric emptying of the high-carbohydrate meal was significantly faster compared to the high-fat and the high-protein meals, which is consistent with current literature [10]. This may be due to the composition of the meal. Fat and amino acids stimulate the secretion of cholecystokinin, which slows the gastric emptying by “relaxing the proximal stomach, contracting the pylorus, or both” [18].

Although no significant difference in gastric half-emptying times was found between the high-protein and the high-fat meal, 14 participants showed complete gastric emptying 6 h after consuming the high-protein meal, whereas only 9 participants did so after the high-fat meal. Both meals contained a high percentage of total calorie count derived from fat (51.5% for the high-fat meal and 58.9% for the high protein meal). However, the total fat content was 20 g higher in the high-fat meal, resulting in a higher total calorie intake compared to the high-protein meal. This may explain the overall slower gastric emptying, as previous studies have demonstrated that increases in total fat content [19] as well as the overall energy intake can delay gastric emptying [20]. It has to be noted that this finding is only an observation, and no statistically difference was found.

Even though the high-carbohydrate meal had the greatest weight and volume after meal intake, it emptied the fastest compared to the other meals. This contrasts with previous findings suggesting that a general increase in meal volume and weight (regardless of composition) is linked to a longer gastric half-emptying time [21, 22]. However, in these studies, greater meal weight was also associated with greater total calorie content.

In our study, after consuming the high-fat meal, which was the smallest meal in terms of weight and volume after meal intake, with a total calorie count of 1210 to 1340 kcal, gastric half-emptying time was reached after 187.84 min. By comparison, gastric half-emptying time was 132.35 min for the high-carbohydrate meal (440 kcal) and 157.57 min. for the high-protein meal (730 kcal).

These findings may indicate that within the tested meals, factors like meal composition (especially the total fat count) and the total calorie count may be more decisive in delaying gastric emptying times than meal volume and weight.

Complete gastric emptying in healthy subjects mostly occurred between 6 and 8 h across all meal types. This is slower compared to the current literature, in which a ‘normal’ sized meal typically empties within 3 to 5 h, and corresponds to the gastric emptying time of a large meal ranging from 5 to 8 h [10]. However, the authors did not define “normal size”, which complicates a direct comparison. In this study, meal portions procured from restaurants were referenced as ‘normal’ or ‘typical’ meals. One explanation may be bigger portion sizes in restaurants or the increase in portion sizes in the last decades [23].

On average, women showed slower gastric emptying than men, but these differences were only significant in the high-protein meals. These findings are consistent to those of Vasavid et al., who reported significant longer gastric half-emptying times for solid meals in women compared to men using gastric emptying scintigraphy [24]. Further analyses showed that women in the luteal phase of their menstrual cycle as well as women on contraceptive medication had significantly prolonged gastric half-emptying times compared to women in the follicular phase, which may be explained by the influence of sex hormones [25]. Contrary to these findings, Horowitz et al. did not find any statistically significant differences in gastric emptying in a normal menstrual cycle [26]. Madsen also did not find any differences between male and female gastric emptying times [27]. However, this study only included women in their follicular phase.

In our study we did not collect data on the menstrual cycle of the female participants. This is a limitation of this study, as the menstrual phase could mask any differences between the sexes. Because of these heterogenous findings in the literature, when estimating the time of death, it should be considered that women may show slower gastric emptying. However, further studies are needed to investigate the effect of gender on gastric emptying.

The effect of BMI on gastric emptying also remains controversial. In a study of 90 participants, Hellmig et al. could not find a significant correlation between gastric emptying times (determined by 13C breath test) and BMI for solid meals [28], while Maddox et al. found a delayed gastric emptying in obese participants using gastric emptying scintigraphy [29]. Due to the small sample size in our study, no statistical analysis of BMI could be performed. However, our descriptive findings are in accordance with Wright et al., who found an accelerated gastric emptying of solid meals in obese participants in a scintigraphic study [30].

Participants in the present study were allowed to stand, sit, or walk to mimic the movement of everyday life. A meta-analysis of 20 studies found accelerated gastric emptying for low-intensity exercises like walking [31]. However, the included studies mostly investigated the effect of liquid meals, so its applicability to solid meals remains uncertain. Nevertheless, when applying gastric emptying times to forensic cases, factors such as physical activity as well as body positioning (e.g. lying supine while sleeping) should be considered, as it may influence the gastric emptying of a solid meal when consumed with a nutritive liquid [32, 33]. However, gastric emptying of a solid meal consumed without a nutritive liquid does not seem to be influenced by posture [22, 34].

MRI has been validated as a method for measuring gastric emptying of a mixed solid/liquid meal [13]. Unlike the gold standard scintigraphy, MRI does not expose individuals to ionizing radiation and is more robust than ultrasonography in suboptimal conditions such as obesity or the presence of intragastric air [35].

Furthermore gastric content volume may appear larger than the ingested meal volume due to secretion [36]. This was also demonstrated in an MRI study by Goetze et al. [37], using liquid test meals.

In contrast to methods such as scintigraphy or breath tests, which only assess the gastric emptying of the labeled meal, MRI measures the total gastric content volume, including secretions [38–40]. Since in autopsies the total gastric content volume is also determined (including salivary and gastric secretions) [12], MRI-based volume measurement seems advantageous in forensic research investigating gastric emptying times.

In this study, participants were allowed to drink water ad libitum, to mimic real life behavior and to improve comfort. In addition, fluid consumption with and after meals is common in daily practice. Fisher et al. demonstrated in a scintigraphic study that the emptying of a solid meal is not influenced by water [41].

However, the measurement points may still have been influenced by water consumption shortly before the MRI scan, potentially resulting in an overestimation of volume. This could particularly explain the noted increase in volume at the 8-hour mark. The effect of liquids other than water on gastric emptying of the solid meals were not investigated. Particularly the consumption of alcohol (ethanol) may delay gastric emptying of a solid meal [42] and should be considered when found in autopsies.

As most of the studies on gastric emptying times, the present study only included healthy participants with no history of medical conditions that might influence gastric emptying.

However, several non-meal-related factors that influence gastric emptying were not accounted for in this study.

One participant showed a delayed gastric emptying while suffering from migraine symptoms. Although anecdotal, this observation is consistent with previous findings in which migraine slowed gastric emptying and may contributed to migraine associated symptoms such as nausea or vomiting [43]. This observation emphasizes that personal factors play a significant role in gastric emptying and must be considered when estimating the time since death. Many factors have been reported to alter gastric emptying such as gastric surgery, medication use or diabetes [11]. Therefore, for a reasonable estimation of time since death, it is necessary to investigate for potential factors that might have altered gastric emptying e.g. in medical records or in autopsy findings [12].

Stomach content based death time estimation should only be used alongside other methods to establish a possible timeframe of death or as corroborative evidence [2, 11, 12]. As with other methods for death time estimation [44, 45], gastric emptying cannot be used to determine an exact time, but rather an interval of several hours [46]. Naturally, this approach requires that the time of the last food intake is known.