Just on the basis of the perspective that the calorie content of an ingested liquid may be the primary factor influencing the gastric emptying rate, the gastric emptying of whisky may have a similar pattern to that of a calorie-free beverage, such as water, because it only includes alcohol with no calories before being absorbed and metabolised. In the present study, the gastric emptying time of whisky with water was shorter than that of the same volume of the isocaloric glucose solution, as anticipated, but was slower than that of the same volume of water, indicating that some factors present in whisky delayed emptying.
Whisky includes only alcohol (ethanol) and none of the three major nutrients, namely, proteins, fats and carbohydrates. Therefore, whisky may be nutritionally deemed a calorie-free beverage before being absorbed from the gastrointestinal tract. Alcohol acts as a source of energy equivalent to approximately 7 kcal/g only when it is metabolized in the liver. In the liver, alcohol is metabolized in the order of acetaldehyde, acetate, and the end products of water and carbon dioxide. Since acetate derived from this metabolic process is quickly utilized in the tricarboxylic acid cycle, any metabolic products are never stored as an energy source . In contrast, brewed liquors, such as beer and wine, include nutrients that act as an energy source per se, in contrast to alcohol, and, thus, each gastric emptying time is expected to depend on the calorie content. A previous study reported that the gastric emptying time of beer and red wine was significantly longer than that of ethanol under the condition that volumes and alcoholic contents were both uniform, while that of beer, which has a lower calorie content, was shorter than that of wine .
Calorie intake is a regulator of the gastric emptying time. Previous studies demonstrated that liquid gastric emptying chiefly depended on the total amount of calories regardless of compositional differences [7-10]. The small intestine chiefly performs digestion and the absorption of water and nutrients, whereas the stomach breaks, stirs, and preserves ingested materials to promote smooth digestion and absorption in the small intestine. If large amounts of ingested nutrients are flowing into the small intestine at once, metabolic abnormalities, including hyperglycaemia, will occur. Dumping syndrome after gastrectomy is one of these pathological conditions. When nutrients are absorbed in the proximal and/or distal small intestine, various gastrointestinal hormones, such as secretin, gastric inhibitory peptide, cholecystokinin, glucagon-like peptides, and peptide YY, are secreted as a feedback mechanism, thereby allowing for the appropriate digestion and absorption of nutrients [19-22], which suppresses the motility of the stomach and upper jejunum. One of those feedback systems is called the “ileal brake” .
Based on these two standpoints, the gastric emptying pattern of whisky with water is expected be closer to that of water when adjusted to the same volume. In the present study, the gastric emptying time of whisky with water was significantly slower than that of water alone; therefore, the effects of alcohol need to be considered. Although abnormal motility, mucosal damage, and increased permeability occur in the digestive tract following the consumption of alcohol , gastric motility exhibits two very different patterns depending on the alcoholic content. Bujanda and co-workers showed that gastric motility was inhibited by the intake of alcoholic beverages with a density of more than 15%, but was promoted at lower densities . Franke and co-workers reported that the gastric emptying times of ethanol adjusted to low alcoholic contents of 4 and 10% were longer than that of water, and no significant differences were observed in gastric emptying times in the range of 4 -10%; however, the underlying mechanisms remain unclear . In the present study, we used whisky with water corresponding to a low alcoholic content of 8%. Although gastric motility is expected to be facilitated by a low alcoholic content, the gastric emptying of whisky with water was significantly longer than that of water in the present study. The following two major factors may be contributing to this phenomenon. The stomach is one of the principal absorption sites of ingested alcohol and has the ability to metabolize ethanol by alcohol dehydrogenase (ADH), such as ADH1C, ADH3, and ADH4, despite a low metabolic capacity, suggesting that absorption and metabolic processes in the stomach induced delayed emptying against enhanced gastric motility [23, 24]. This insight may be important for the liquid gastric emptying of alcoholic beverages. Furthermore, the osmotic pressure of liquids is a factor that inhibits gastric emptying [25-27]. Previous studies have shown that differences in gastric emptying times due to osmotic pressure were markedly smaller than those due to calorie content [26, 27]; however, a large difference in osmotic pressure significantly affects gastric emptying rates . Since the osmotic pressure of ethanol is 165 mosm/L per 1% , the osmotic pressure of whisky with alcohol used in the present study was calculated to be at least 1320 mosm/L, which is more than 132-fold that of water (10 mosm/L). This large difference results in the slower emptying of whisky with water. Further studies that investigate other factors are required.
There were some limitations in the present study. The number of subjects (n=10) examined was small and all were physically and mentally healthy. Therefore, the results of the present study may not be applied to individuals with alcohol allergies or intolerances or patients including those receiving anaesthesia and undergoing surgery. Furthermore, since the number of subjects (n = 10) examined was small, the present study is a type of exploratory study.