Your Digestive System and How It Works

What is the digestive system?


The digestive system

The digestive system is made up of the gastrointestinal (GI) tract—also called the digestive tract—and the liver, pancreas, and gallbladder. The GI tract is a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine—which includes the rectum—and anus. Food enters the mouth and passes to the anus through the hollow organs of the GI tract. The liver, pancreas, and gallbladder are the solid organs of the digestive system. The digestive system helps the body digest food.

Bacteria in the GI tract, also called gut flora or microbiome, help with digestion. Parts of the nervous and circulatory systems also play roles in the digestive process. Together, a combination of nerves, hormones, bacteria, blood, and the organs of the digestive system completes the complex task of digesting the foods and liquids a person consumes each day.

Why is digestion important?
Digestion is important for breaking down food into nutrients, which the body uses for energy, growth, and cell repair. Food and drink must be changed into smaller molecules of nutrients before the blood absorbs them and carries them to cells throughout the body. The body breaks down nutrients from food and drink into carbohydrates, protein, fats, and vitamins.

Carbohydrates. Carbohydrates are the sugars, starches, and fiber found in many foods. Carbohydrates are called simple or complex, depending on their chemical structure. Simple carbohydrates include sugars found naturally in foods such as fruits, vegetables, milk, and milk products, as well as sugars added during food processing. Complex carbohydrates are starches and fiber found in whole-grain breads and cereals, starchy vegetables, and legumes. The Dietary Guidelines for Americans, 2010, recommends that 45 to 65 percent of total daily calories come from carbohydrates.

Protein. Foods such as meat, eggs, and beans consist of large molecules of protein that the body digests into smaller molecules called amino acids. The body absorbs amino acids through the small intestine into the blood, which then carries them throughout the body. The Dietary Guidelines for Americans, 2010, recommends that 10 to 35 percent of total daily calories come from protein.

Fats. Fat molecules are a rich source of energy for the body and help the body absorb vitamins. Oils, such as corn, canola, olive, safflower, soybean, and sunflower, are examples of healthy fats. Butter, shortening, and snack foods are examples of less healthy fats. During digestion, the body breaks down fat molecules into fatty acids and glycerol. The Dietary Guidelines for Americans, 2010, recommends that 20 to 35 percent of total daily calories come from fat.

Vitamins. Scientists classify vitamins by the fluid in which they dissolve. Water-soluble vitamins include all the B vitamins and vitamin C. Fat-soluble vitamins include vitamins A, D, E, and K. Each vitamin has a different role in the body’s growth and health. The body stores fat-soluble vitamins in the liver and fatty tissues, whereas the body does not easily store water-soluble vitamins and flushes out the extra in the urine.

How does digestion work?
Digestion works by moving food through the GI tract. Digestion begins in the mouth with chewing and ends in the small intestine. As food passes through the GI tract, it mixes with digestive juices, causing large molecules of food to break down into smaller molecules. The body then absorbs these smaller molecules through the walls of the small intestine into the bloodstream, which delivers them to the rest of the body. Waste products of digestion pass through the large intestine and out of the body as a solid matter called stool.

Points to Remember

• Digestion is important for breaking down food into nutrients, which the body uses for energy, growth, and cell repair.
• Digestion works by moving food through the gastrointestinal (GI) tract.
• Digestion begins in the mouth with chewing and ends in the small intestine.
• As food passes through the GI tract, it mixes with digestive juices, causing large molecules of food to break down into smaller molecules. The body then absorbs these smaller molecules through the walls of the small intestine into the bloodstream, which delivers them to the rest of the body.
• Waste products of digestion pass through the large intestine and out of the body as a solid matter called stool.
• Digestive juices contain enzymes that break food down into different nutrients.
• The small intestine absorbs most digested food molecules, as well as water and minerals, and passes them on to other parts of the body for storage or further chemical change. Hormone and nerve regulators control the digestive process.

The Foods To Eat For A Healthy Gut

Our digestive systems continuously extract water and nutrients from an astonishing amount of solid foods and liquids over our lifetimes, all the while fending off nasty microbes and processing waste. What we put into our stomachs is so important that it affects whether we feel well, how flat our bellies are and even our chances of avoiding certain cancers.

When it comes to digestion, women face some unique concerns. “Shifting hormone levels from menstruation, pregnancy and menopause all put a feminine stamp on your digestive tract,” says Dr. Cynthia Yoshida, a gastroenterologist in Charlottesville, Va., and co-author of No More Digestive Problems: The Answers Every Woman Needs. Anatomy also plays a role: Women have the same digestive organs as men, but they are squeezed, along with reproductive organs, into a smaller abdomen. “This means our digestive organs don’t have much give when they get filled with excess gas, air or food,” she notes.

Keeping your stomach healthy, soothed and lean can be as simple as making the right food and drink choices. Here’s how

1. Eat to beat disease: citrus fruit, fibre-rich foods, leafy greens and yellow vegetables
“Strive to get 20 to 25 grams of fibre a day,” says Yoshida. Why? For one thing, it may help protect against cancers. One 2007 study found that a high fibre intake was associated with a decreased risk for esophageal and gastric cancers. And citrus fruit appears to have a protective effect against stomach cancer, according to a survey of studies published in the March 2008 issue of Gastric Cancer.

• Fibre is important for our overall digestive health—particularly in preventing constipation—not just for cancer prevention. Whole grains, spinach, cauliflower, carrots, wheat bran, apples, broccoli, beans, figs and pears are all great fibre sources. “Start slowly, adding more fibre every few days, and drink lots of water. This will help prevent the gas, cramping and bloating that can occur if you add fibre too quickly,” advises Yoshida.

• Recent studies suggest that eating light green, dark green and yellow-coloured vegetables help add up to a healthy stomach, too. These vegetables tend to be rich in carotene, vitamins C and E, and folate, which may help protect the stomach from cancer.

• Preliminary lab research shows that juices—cranberry and raspberry juices, for example—contain compounds called phenols that may prevent GI pathogens such as salmonella. And resveratrol, an antioxidant that is found in red wine, may zap stomach pathogens while leaving the healthy bacteria alone, according to a 2007 study from the University of Missouri–Columbia.
Aim for at least three servings of a whole-wheat or whole-grain food per day to help boost fibre intake. A slice of bread or 30 grams (one ounce) of breakfast cereal makes one serving.

2. Help the good bugs: yogurt, sauerkraut, miso, bananas, garlic, asparagus, onions
About 100 trillion bacteria call your gut home—improve the ratio of good to bad bacteria by eating foods that contain probiotics (various types of healthy bacteria). Probiotics, which include lactobacilli and bifidobacteria, keep the lining of the colon healthy and may improve gut motility and sensation. While much of the research has centred on intestinal health, studies point to potential positive effects on the mouth and stomach, too.

• “The good bacteria in fermented foods like yogurt, miso and sauerkraut can make it through the gastric acid to the colon, where they go to work,” says Yoshida. “There are some claims that the acid in your stomach kills the probiotic bacteria in food and that’s why you should take supplements instead, but that’s not true.”

• “In principle, there is no difference between probiotics taken as a supplement and those in food,” says Michael Gänzle, Canada Research Chair in food microbiology and probiotics at the department of agriculture, food and nutritional science at the University of Alberta. “In practice, it is easier to keep high cell counts during the product’s shelf life if they are in a supplement.” Experts recommend you use a product that contains one million to one billion live cultures. “But the market is unregulated; the consumer has to trust that the product contains live cultures that remain throughout the shelf life,” explains Gänzle. “Try a product and see if you feel better. If you don’t, try another.”

• To support the growth of probiotic bacteria, also choose foods known as prebiotics that naturally contain lots of soluble fibre, such as bananas, garlic, asparagus, Jerusalem artichokes, honey, leeks and onions. Foods such as cheese and cereal bars that are labelled “prebiotic” usually have added inulin, a soluble fibre most often extracted from chicory root.
3. Choose foods that soothe: caraway, cardamom, cinnamon, cumin, fennel, ginger, mint, nutmeg, oatmeal

“Try foods called ‘carminatives’ that prevent or relieve gas, and are used to help the digestive process,” says Jennifer Salib Huber, a registered dietitian and naturopathic doctor in Dartmouth, N.S. “Cumin, for example, helps with the digestion of black beans, which is why they’re often found in recipes together. Other carminatives include caraway, nutmeg, cinnamon and cardamom.”

• Ginger is a traditional nausea remedy, and new studies are backing up the claims. Research shows that it can help quell nausea due to pregnancy, chemotherapy and operations. A 2008 study published in the European Journal of Gastroenterology & Hepatology found that when healthy volunteers took ginger capsules along with a bowl of soup, their stomachs emptied more quickly. This may be useful for treating gastro-paresis, or delayed stomach emptying, a side effect of diabetes.

• “Oatmeal is a ‘demulcent,’ which means it gets slippery in water, helping to coat and soothe the stomach,” says Salib Huber. Cooked oatmeal is your best bet, rather than cookies or granola bars where the oatmeal is dry.

• Peppermint leaf and oil have long been used to help relieve digestive disorders by relaxing stomach muscles. However, avoid peppermint if you’re prone to heartburn—those same relaxed muscles can allow more stomach acid to move up through the esophagus, says Yoshida. “The small amount of flavouring in mint gum or antacids shouldn’t cause problems,” she adds.

To soothe motion sickness, chew a one-inch (2.5 cm) piece of peeled raw ginger, or candied ginger, several hours before—and every four hours during—travel.

4. Eat foods to flatten your tummy: avocado, brown rice, dark chocolate, nuts, oatmeal, olive oil, seeds
Choose foods from the Mediterranean diet—lots of fruit, whole grains, vegetables, legumes, olive oil and low-fat cheese and yogurt; plus a moderate amount of fish, eggs, poultry, sweets and wine; and small amounts of meat. That, along with a daily exercise routine, will help you maintain a healthy body weight, advises Yoshida.

• “If you lose weight, your GI tract will feel better. Carrying less weight helps prevent abdominal discomfort—that full, bloaty feeling—and acid reflux,” says Yoshida. Extra abdominal pounds increase pressure on the lower esophageal sphincter, which separates the stomach from the esophagus. That pressure makes the valve open more often, allowing food and acid from the stomach to backwash into the esophagus, causing heartburn.

• Carrying excess fat in your midsection—even if your weight is within a normal range—puts you at risk for premature death, according to an American study of 44,636 women published in 2008. It concluded that women with a waist size of 35 inches (89 centimetres) or greater were twice as likely to die from heart disease and cancer, when compared to women with a waist size of less than 28 inches (71 centimetres). (To measure it, wrap the tape measure around your waist, above your belly button.) Belly fat can also boost your chances of developing chronic diseases such as diabetes and heart disease.

• Some foods may actually help target your tummy fat. A 2007 study published in Diabetes Care revealed that a diet rich in monounsaturated fats (MUFA), particularly olive oil, prevented fat from accumulating around the abdomen. Other sources of MUFA include avocados, olives, dark chocolate, sunflower oil, and nuts and seeds such as walnuts, flaxseeds and sunflower seeds. In a 12-week diet study, published in the American Journal of Clinical Nutrition in 2008, half of the obese participants ate whole-grain foods such as brown rice and oatmeal, and half ate refined grains such as white rice and bread. Both groups lost weight, but the whole-grain group lost significantly more abdominal fat.