After you eat, you must digest the food: you break the food apart and reduce it to a state from which you can absorb the nutrients into your blood stream, which transports the nutrients to all parts of your body.
Each nutrient combines and interacts with other nutrients and chemicals to create still other chemicals and compounds, which your body uses to build and repair your cells, bones, tissue, and organs. This process is called metabolism. Each metabolic reaction is started, controlled, and terminated by enzymes.
Metabolic enzymes exist throughout your body in your organs, bones, blood, and inside your cells. These enzymes direct the growth of new cells and the maintenance of all tissue. Every organ and tissue has its own group of specialized enzymes that run and maintain it.
Digestive enzymes are a type of metabolic enzyme that are made by your body’s organs and secreted by your salivary glands, stomach, pancreas, and small intestine. They are active only within your digestive system, and they serve to break down your food so that you can absorb it through the walls of your small intestine into your blood stream.
Food enzymes exist within food. Most raw food contains enough natural enzymes to digest that food. When you cook the food, the enzymes are destroyed and can no longer assist in the digestive process. If you eat a meal consisting of a salad and a baked potato, there are likely enough food enzymes contained in the salad to digest it, but there are no extra enzymes available to help digest the baked potato, so your body must create the digestive enzymes needed to handle the task.
Your body’s top priority is digesting food and converting it to enough nutrients to run its systems. This takes 80% of your body’s energy, and a lot of enzymes, particularly if the body must make most or all of these enzymes. If you are run down, under stress, living in a very hot or very cold climate, pregnant, or are a frequent air traveler, then your body requires extra enzymes. The more you depend on your internally generated digestive enzymes, the more stress you put on your body, and the less time your body has for replacing damaged cells and keeping your immune system strong. Aging also deprives us of our ability to produce necessary enzymes.
Carbohydrates, proteins, and fats are the three macro-nutrients that make up the bulk of your daily diet. To metabolize these nutrients, we also need an adequate source of the major types of digestive enzymes: amylases, proteases, and lipases.
Carbohydrate digestion begins in your mouth and proceeds through the digestive tract, as most carbohydrates are broken down into their simplest forms for use as fuel. Insoluble fiber is eliminated through excretion.
Breaking up the long polysaccharide chains of complex carbohydrates begins in your mouth, with the enzyme salivary amylase. Chewing physically breaks carbohydrates into smaller pieces, creating more surface area for salivary amylase to begin working. After you chew, you swallow the carbohydrates, which pass through your esophagus into your stomach, where stomach acid stops the effectiveness of salivary amylase. No additional carbohydrate digestion occurs until the mixture moves from your stomach into your small intestine.
Your pancreas releases an enzyme called pancreatic amylase into your small intestine, where it continues breaking down long saccharide chains into disaccharides, or dual-molecule sugars such as sucrose. Additional enzymes, including lactase, maltase, and sucrase, then break disaccharides down into monosaccharides, or single-molecule sugars such as glucose. These monosaccharides are absorbed by the villi, small finger-like protrusions in the intestine. They move to your liver, where they are stored as fuel to be used by your body.
Lactase is the enzyme that metabolizes lactose into glucose and galactose. Most mammals stop producing lactase after weaning. An estimated 75% of human adults worldwide show a decrease in lactase production during adulthood, including 5% of northern Europeans, 71% of Sicilians, and more than 90% of some African and Asian populations. Therefore, the majority of adults are unable to fully digest lactose, a sugar found in milk and other dairy products. For us, consuming dairy products causes symptoms such as abdominal bloating and cramps, flatulence, diarrhea, nausea, rumbling stomach, or vomiting, and may be a significant cause of irritable bowel syndrome. People in northern Europe probably retained the ability to produce lactase into adulthood through natural selection. Crop failures during ice ages caused people to turn to the unnatural act of drinking the milk of other animals to survive. The humans who were able to tolerate this without vomiting survived and reproduced, passing on their abilities to their children. I inherited the normal gene for adult-onset lactose intolerance from my Italian mother. I consume no dairy, and I am much healthier now than when I tried to hold my nose and drink milk.
Proteases are a group of the digestive enzymes whose function is to break down protein. Protein digestion begins in your stomach, primarily with the action of the hydrochloric acid that is produced there, and by the enzyme called pepsin. The protein-containing foods are broken apart, separating out the protein, then the proteins are broken into their constituent parts, the amino acids, through hydrolysis. Hydrolysis involves the insertion of a water molecule between two amino acids, which forces the bond between them to break.
Your pancreas produces two other proteases, trypsin and chymotrypsin, and secretes them into the upper portion of the small intestine, where they continue to hydrolyze proteins. Because amino acids have very small dimensions, they are able to penetrate the intestinal lining. The amino acids are absorbed through selectively permeable membranes of the small intestine walls, which are arranged in folds called villi, by the blood in the capillaries of the small intestines, carried through the liver, and then go into general circulation.
Proteases can break down undigested protein, cellular debris, toxins, and certain bacteria and viruses in the blood, sparing the immune system this task. The immune system is then free to fight other infections.
Many plant seeds contain protease inhibitors that interfere with the absorption of their valuable proteins. These serve to protect the seed from being digested by an animal so that it is deposited intact in manure fertilizer, far from the parent plant to propagate. Protease inhibitors also combat cancer by preventing the synthesis of key proteins required for cancer cells to divide. Protease inhibitors block the initiation of the cancer process and also destroy premalignant cells. Soaking seeds in water to the point of germination greatly reduces the protease inhibitors, as does cooking seeds.
Lipase is the digestive enzyme that hydrolyzes fats. Fats are often large, complex molecules, and their digestion usually takes longer than that of simpler molecules like carbohydrates. Fats are also hydrophobic molecules, meaning that when they are placed in water, they clump together into large aggregates, reducing the amount of surface area exposed to water. The first step your body takes to digest fats is to break up these large clumps. Your body accomplishes this process using compounds called bile salts, which are produced by the liver. Bile salts dissolve the clumps of fat into tiny droplets.
The small droplets are often in the form of molecules called triglycerides, which is made up of a glycerol molecule and three fatty acids. Fatty acids are a type of molecule known as a carboxylic acid, which has a long chain of carbon atoms. The next step of digestion is to break these triglycerides into simpler molecules. Your pancreas produces an enzyme called lipase, which hydrolyzes triglycerides into monoglycerides (one fatty acid attached to a glycerol molecule) and free fatty acids.
The monoglycerides and fatty acids remain dissolved in bile salts and form small droplets known as micelles. As the micelles travel through the digestive tract, they come into contact with the cells that line the digestive tract, and these cells absorb them through their cell membranes.
After intestinal cells have absorbed the monoglycerides and fatty acids, they reassemble them into triglycerides, the form of fat most commonly found inside your body. For transport, your body packages triglycerides together with protein and cholesterol into particles called chylomicrons. The intestinal cells then secrete chylomicrons into the lymph vessels, which eventually flow into the bloodstream. Once fats are in your bloodstream, your body can transport them to wherever it needs them, breaking them down for energy or storing them as fat.
To maximize your digestive and food enzymes, eat at least one large salad every day, at least three servings of fresh raw fruits, especially berries, every day, generous amounts of cooked green vegetables, beans, onions, and mushrooms every day, and 1-2 ounces of raw nuts and seeds each day. Avoid refined grains, sugar, artificial sweeteners, meat, dairy, and eggs. Limit oil to one teaspoon or less per day, if any.
This blog uses the latest nutritional data available from the USDA (United States Department of Agriculture), and the FDA (United States Food and Drug Administration), as well as nutritional data provided by food growers and manufacturers about their products. We believe the information on this blog to be accurate. However, we are not responsible for typographical or other errors. Nutrition information for recipes is calculated by Living Cookbook based on the ingredients in each recipe based on statistical averages. Nutrition may vary based on methods of preparation, origin and freshness of ingredients, and other factors.
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