A tale of gastric layering and sieving: Gastric emptying of a liquid meal with water blended in or consumed separately

- Nutrient rich liquid meals may layer separately from water intragastrically post ingestion.
- The nutrient poor layer may be emptied from the stomach first.
- The gastric emptying is quicker because there are less nutrients in the fluid.
- This quick emptying can be prevented by mixing in the water before ingestion.
- Gastric layering of fluids may influence indirect emptying measurement methods.

BackgroundThe process of gastric emptying determines how fast gastric content is delivered to the small intestine. It has been shown that solids empty slower than liquids and that a blended soup empties slower than the same soup as broth and chunks, due to the liquid fraction emptying more quickly. This process of 'gastric sieving' has not been investigated for liquid foods.ObjectiveTo determine whether gastric sieving of water can also occur for liquid foods.MethodTwo groups of men participated in a parallel design (n = 15, age 22.6 ± 2.4 y, BMI 22.6 ± 1.8 kg/m2, and n = 19, age 22.2 ± 2.5 y, BMI 21.8 ± 1.5 kg/m2) and consumed an isocaloric shake (2093 kJ, CARBOHYDRATES: 71 g, FAT: 18 g, PROTEIN: 34 g), either in a 500-mL version (MIXED) or as a 150-mL shake followed by 350 mL water (SEPARATE). Participants provided appetite ratings and were scanned using MRI to determine gastric emptying rate and volume at three time-points within 35 min post ingestion.ResultsGastric emptying the percentage emptied in 35 min was significantly smaller for MIXED (29 ± 19%) than for SEPARATE (57 ± 11%, p < 0.001).ConclusionIn the present study we show that gastric sieving can occur for liquid foods; water is able to drain from the stomach while a layer of nutrient rich liquid is retained. In indirect gastric emptying measurements, the behavior of labelling agents may be affected by the layering and confound emptying measurements.