Once undergoing the critical step of being properly chewed, the semiliquefied food mass is squeezed down a muscular tube, the esophagus, to the stomach. The stomach is a far more sophisticated organ than most think. Rather than just being a passive sack for the groceries, the stomach plays a very active role in promoting proper digestion.
The human stomach actually has two successive functional compartments. The first portion of the stomach, the anterior part, has less muscle in the wall and will expand to allow a temporary storage of the food mass. The effects of stomach enzymes and acidity are less pronounced here, and the salivary ptyalin enzyme action can still remain active. However, before long, the food proceeds into the lower, posterior stomach, which is more muscular. The gastric juices, containing mucus, strong acid, and acid-activated protein-busting enzymes, then begin their work on the food mass.
6 Optimal Nutrition for Optimal Health
However, this substantially occurs only if adequate protein is present in the food mass to reflexly stimulate the flow of the gastric juices. If starch alone is eaten, less of the acidic gastric juice will be reflexly released, and the starch digestion can proceed. More gastric juice produces a more strongly acid environment, which will shut down the activity of starch-busting enzymes that are present. Increasingly complex foods can present a wide range of protein content to the stomach. Virtually all foods contain at least minimal to trace amounts of protein, and the amount of acid formed in the stomach will be related to the absolute amount of protein presented to the stomach.
Lavers et al. determined that different foods of equal caloric value provoked vastly different acid secretion responses in the stomachs of dogs.1 Relative to a beef meal standard, haddock resulted in 100 percent more acid secretion, chicken 20 percent more, vegetables 25 to 50 percent less, butter 60 percent less, and fruits 75 to 85 percent less. At rest, in the absence of any food, the stomach tends to be pH neutral, with only minimal, if any, acid present.
Another mechanism that helps to determine the acid content of the stomach relates to the acidity level of the food that was eaten. The more acidic the food eaten, the less acid the stomach will generate. A high-protein food will be less well digested in the stomach if it is eaten with a highly acidic food such as sauerkraut, since the stomach will reflexly form less acid as well as less protein-digesting enzymes in response to the presence of such an acidic food. You will see that this principle is very important in reaching complete digestion through the understanding of proper food combining, to be addressed in chapter 2.
In addition to exposing the food mass to the digestive enzymes of the stomach, the musculature in the lower, posterior stomach squeezes and churns the food, mixing it even further with the gastric acid and enzymes. This further promotes a greater meeting of the surface area of the food with the enzymes, which is directly
The Importance of Proper Digestion 7
related to how effective those enzymes can be in breaking down the food. In a sense, this active massage of the food helps to continue the "chewing" of the food after it leaves the mouth.
The primary digestive enzyme activated by the stomach acid is pepsin. Pepsin serves to break down proteins, which are long strings of amino acids linked together, into smaller amino acid sequences called peptides. These peptides, along with the rest of the digesting food, then await the next stage of the process. A strong muscular sphincter at the bottom of the stomach, the pylorus, prevents any premature release of the stomach contents.
Before proceeding to the next portion of the digestive pathway, the intestinal tract, it is also important to know a little about how the stomach empties. The pylorus at the bottom of the stomach serves not only to keep food from getting out of the stomach too prematurely, it also serves to let only a little of the digesting food, or chyme, into the intestinal tract at a time. Food does not just digest in the stomach for a while and then quickly get dumped out all at once. As the food gets progressively digested in the stomach, the pylorus senses this and lets a little at a time out of the stomach. Once the food mass has adequately liquefied and the food particles remaining have become small enough, the pylorus will start squirting no more than a teaspoon of chyme every thirty seconds or so out of the stomach. You will see why this is important after you understand some of the food combining principles discussed in chapter 2.
No comments:
Post a Comment