Just shards of recent Itlian studies to illustrate the complexity of the topic:
Prof L. Benini (University of Verona) in two studies, each on 8 subjects, observed the stomach emptying after a solid/mix meal of 700-870 kcal., and he found that the “normal” value for the emptying of 50% of stomach content was 186 minutes (± 44 min*) if the meal contained 4 grams of fibres. But for a similar 700-870 kcal meal containing 20 grams of fibres, the normal time for 50% content emptying would be 231 minutes (±49 min*). Technique for measurement is the ecography with measurement of antral diameters. Note the very high errors.
In another 10-subject study, Prof. R. Ricci (University of Rome), found that with a meal of 1050 kcal (solid+ liquid) the normal value to achieve a reduction of stomach content to 60% is would be 300 minutes (similar measurement technique: antral volume ecography).
The measurement is an issue. The G.I.S.M.A.D (Gruppo Italiano per lo studio della motilità dell’apparato digerente) defines schintigraphy (radiograpfic analysis) as “inaccurate”.
One should also be aware that literature studies create homogeneous groups, and results are thus referred to homogeneous starting conditions, like: patients who have not been eating for the previous 12 h., a meal that is not followed by other subsequent meals (no further continuous or discontinuous food assumption), no contemporary or subsequent alcohol assumption, similar kind of meals and controlled meals…. While other researches exist to investigate how inhomogeneous ways of food assumption can influence the expected figures in various ways.