This is an experimental crossover clinical trial design. Inclusion criteria were being male; with normal nutritional status assessed by BMI (body mass index between 20 and 30 kg/m2); age ranging from 18 to 30 years old; healthy with no acute disease during the 3 months before the study, and without having gastroparesis or other gastric motility disorders. All these conditions were assessed by a questionnaire containing questions about health status. We planned to exclude participants who did not complete the study; did not comply with the experiment procedures; or who consumed alcoholic beverages on the day before the study. We also excluded those who have metallic prosthesis of any kind, including any tiny metal fragments in the body or complaining of anxiety disorders indoors or phobia to magnetic resonance imaging (MRI).
The data were collected in three phases. Firstly, after a fasting period of 8 h, the participants attended the Radiology Service of the Hospital de Cancer, Cuiaba, Brazil, to perform MRI images of the upper abdomen with the objective of measuring the fasting status GRV (phase 1). In this phase, adequate stomach motility was observed to exclude cases of possible gastroparesis that could interfere with gastric emptying and expected results. GVR (cm3) was evaluated by tracking each slice’s region of interest (ROI), forming a volume by the sum of all ROIs. In phase 2, which was immediately after phase 1 each participant while still inside the MRI exam room ingested 200 mL of one of these two clear supplements formula depending of the phase as follows: phase 2.1) 12.5% maltodextrin (25 g)–CHO group or phase 2.2) the intervention drink containing whey protein and carbohydrates as described below. All participants participated of phase 2.1 and phase 2.2. For that, a week interval was programmed between phase 2.1 and phase 2.2. Immediately after drinking the supplement (in phase 2.1 and phase 2.2), the individual was immediately positioned in the supine position and another MRI scan for measurement of GRV was done. Finally, phase 3 was performed after a 3-h pause after the ingestion of the oral supplements. A third MRI scan of the upper abdomen was done to measure again the GVR as previously described.
Intervention oral supplement
The oral supplement used as an intervention for the study group (WP + CHO group) was Nutren Fresh (Nestlé, São Paulo, Brazil). This oral non-residual supplement (clear fluid; 698 mOsm/L) has 100% whey protein isolated from total proteins, with various vitamins (B1, B6, C, D, niacin, and folic acid) with a “lemon tea” flavor. In addition, the formula contains no lactose or lipids; is formulated with a volume of 200 ml, with a caloric density of 1.28 kcal/ml; protein: 10 g in 200 ml of the product (100% whey protein isolate); and carbohydrate: 54 g in 200 ml of the product (74% glucose syrup and 26% maltodextrin). For control within a week interval, all participants went through the three phases of the experiment using a supplement containing 25 g of maltodextrin plus 200 mL of water (12.5%, 50 kcal per 100 ml and 285 mOsm/L; CHO group).
All exams were performed using the same MRI equipment which was a Magnetom Essenza 1.5 T device; Siemens Healthcare (Brazil). Each volunteer was placed in a supine position, with a body coil (Body Matrix) to capture the signal. Cross-sectional acquisitions with 40 slices (perpendicular to the longitudinal axis of the body) were performed in echo-planar fast spin echo (HASTE) sequences with a slice width of 4.0 mm at 3.0 mm intervals. This STEAM sequence (TR [repetition time] 774 ms, TE [echo time] 92 ms) visualizes fluids with hypersignal as opposed to the low signal from adjacent organs. Each acquisition of a set of images was performed during 15 s of apnea. The images were captured by an industry technician with MRI experience and reviewed by a radiologist to confirm that the images covered the entire stomach. The GRV was assessed by tracking each slice’s region of interest (ROI), forming a volume by the sum of all ROIs. GRV measurements in milliliter were performed manually by tracing regions of interest on each slice using OsiriX MD ANVISA v.12.0.3 software and summing the slices to determine the total gastric volume and the results were entered into an Excel data sheet for statistical analysis.
Categorical variables were summarized by absolute (n) and relative (%) frequencies. Continuous were expressed as means and 95% confidence interval (95%CI) or standard deviation (SD). ANOVA for repeated measures was used to compare GRV in the three phases. Additionally, paired and unpaired t tests were done to assure within and between groups comparisons and adjust possible inflation of alpha error. The value of p for within-measures and between-measures analysis was calculated for analysis. For all analyses, p < 0.05 was considered statistically significant. All statistical analyzes were performed using SPSS for Windows 20.0 software (SPSS, Chicago, IL, USA).