Additional liquids should not be taken with any meal. The more liquid you drink, the more you dilute the enzymes that are doing the work of digestion. The potency of any enzyme is directly related to its concentration. Water, or just about any other liquid, will stop stomach digestion dead in its tracks when you swallow a large enough amount of it at mealtime. And as the digestion slows, the opportunity for food rotting increases.
Liquids can also impair digestion in other ways. Enzymatic activity is typically enhanced by heat, and impaired or stopped by cold. The glass of water served with your meal in a restaurant usually has ice in it. Double whammy. The enzymes get diluted and chilled into inactivity simultaneously.Liquids can also be acidic or alkaline. Obviously, such liquids can directly affect the pH of the stomach contents above and beyond any dilution or chilling effect the liquid might have. Enzyme activity will decrease the further its environment gets from its optimal activating pH. And remember that any acid added to the stomach contents will further inhibit the stomach's release of its own acid, gastric juice, and gastric enzymes.
Liquids impair digestion by still another mechanism. The very presence of protein in the stomach further stimulates the secretion of acid and enzymes. However, this stimulation is related to the con-centration of protein presented to the stomach. When significant liquids are ingested with the food and mixed up with it, the protein has a lesser concentration in the total food mass. With a lesser concentration, the signal to the stomach is weakened, and the continued secretion of gastric juice from the stomach cells is decreased. And without adequate amounts of activated enzymes from the gastric juice, protein in the stomach will simply not digest adequately.
Enzyme activity is also favorably promoted the better the stomach contents are mixed. Alcohol can inhibit the ability of the stomach to properly churn and mix its contents. An ice cold beer with dinner can have a strong negative effect on stomach digestion, since it dilutes enzymes, chills enzymes, impairs mixing of the food mass, and decreases further reflex production of more acid and enzymes. Perhaps the belching that so often results from drinking beer during a meal is due as much to the digestion being inhibited as to the carbonation in the beer.The amount of food eaten at a sitting will also directly affect the quality of digestion. The glands in the mouth, stomach, and small intestine are not unlimited in their abilities to form enzymes and other digestive factors. Not surprisingly, the body's digestive capabilities can be overwhelmed by the sheer volume of food, no matter how well chewed or otherwise prepared. This too can result in incomplete digestion. The amount of gastric juice and enzymes that can be produced in response to any meal can be overwhelmed by a large enough amount of food.