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“The pylorus muscle, which works similar to the LES, controls the foods entering the small intestines from the stomach,” Deschamps says. “The pylorus muscle only squirts a small amount of food into the small intestines at a time.”
 The real action takes place in the small intestine, and it is at this point that some other organs get involved. The liver produces a digestive juice called bile, which is stored between meals in the gallbladder. At mealtime, it is squeezed out of the gallbladder into the bile ducts to reach the intestine.
“The gallbladder sends in emulsifiers and bile to break down fat,” Deschamps says. “The pancreas sends in bicarbonate to neutralize stomach acid and enzymes to continue the digestion process even further. The squeezing action of peristalsis keeps the process moving along.”
The majority of the digestive process takes place in the small intestine as the food is dissolved into the juices from the pancreas, liver and intestines. “Some easily digested foods are completely broken down in the upper small intestine,” Cucura says. “The rest of the absorption takes place in the jejunum and the ileum of the small intestine. The small intestine contains fingerlike projections called villi. These villi are covered with hair-like projections called microvilli. Along the microvilli, the broken down nutrients are transferred into the blood stream where they are carried to different parts of the body.”
By the end of the small intestine, there is not much left except water, insoluble fiber and minerals. “The large intestine absorbs the minerals and recycles the water,” Deschamps says.
The remaining components then enter the colon. “The main function of the colon is to absorb water from that material,” Dr. Varanasi says.
What is left is called feces—made up of water, bacteria, undigested matter and dead cells. Feces remains in the colon for a day or two until it travels to the rectum and is expelled with a bowel movement.
How everything breaks down
For a healthy diet, the normal recommendations are that 50 percent of your calories should come from carbohydrates, 20 percent from protein and 30 percent from fats. Of course, these recommendations may change depending on a person’s individual needs.
Examples of carbohydrates are bread, potatoes, legumes, rice, spaghetti, fruits and vegetables. Many of these foods contain both starch and fiber.
Starch is digested in two steps. First, it is broken down into molecules called maltose; then the maltose is split into glucose molecules that can be absorbed into the blood. The bloodstream carries glucose to the liver, where it is stored or used to provide energy for the body.
Proteins such as meat, eggs and beans are made up of giant molecules of protein that must be digested by enzymes and turned into small molecules called amino acids. These amino acids can be absorbed from the hollow of the small intestine into the blood and then be carried to all parts of the body to build the walls and other parts of cells.
Debra Deschamps, R.D.
Ravikant Varanasi, M.D.
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“The old saying, ‘you are what you eat’ really rings true.” —Debra Deschamps, R.D.
Fat molecules provide energy for the body, too. Bile acids from the liver act as natural detergents to dissolve fat in water (think of detergent cleaning a pan full of grease) and allow the enzymes to break the large fat molecules into smaller molecules such as fatty acids and cholesterol. These fatty acids and cholesterol move into the cells of the mucosa and are formed back into large molecules that pass into vessels near the intestine. These small vessels carry the changed fat to the veins of the chest, and the blood carries the fat to storage depots in different parts of the body.
A smoothly running system
How do you know if you are having problems with digestion?
“If your digestive system is not functioning properly, you may experience abdominal pressure, flatulence or nausea after meals,” Cucura says.
Some people may think they are constipated if they don’t have a bowel movement every day, but there is no rule about regularity.
“The usual range is three times a day to three times a week,” Cucura says. “Fewer than three times a week could be related to constipation. More than three watery stools a day could be related to diarrhea.”
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Here are some tips to keep your digestive system healthy:
- Increase your fiber intake. According to the National Center for Health Statistics, the average American eats an average of 5 to 14 grams of fiber daily, and that is nowhere near enough. “It is recommended that you get 25 to 35 grams of fiber per day for the digestive system to function optimally,” Cucura says. You can increase your intake by adding more fruits, vegetables and whole grains to your diet.
- Reduce fats and oils. Excess fat slows digestion, which can lead to heartburn, bloating and constipation.
- Increase your fluid intake. Fluid helps lubricate and transport food through the intestines.
- Watch your alcohol intake. Alcohol can inflame the stomach lining and relax the LES, the muscle that prevents stomach acid from backing up into your esophagus. “Alcohol is an irritant to the stomach and a risk factor for acid reflux,” Dr. Varanasi says. “Alcohol abuse can affect your pancreas and lead to chronic pancreatitis, which can predispose you to diabetes, malabsorption and even pancreatic cancer. It can also affect the liver function, cause fatty liver disease and cirrhosis of the liver.”
- Practice good eating habits. Relax while you eat, eat at regular times and eat moderate portions.
- Maintain a healthy weight. You are more likely to experience bloating, constipation and gastroesophageal reflux disease (GERD) if you are overweight.
- Exercise. “Exercise stimulates the contractions of the intestinal muscles and helping food move through the digestive tract,” Cucura says. “And it improves the carbohydrate metabolism with greater insulin sensitivity.”
- Maintain a healthy lifestyle. Stress, tobacco and some medications can contribute to heartburn, nausea, constipation and other digestive disorders.
- Eat a variety of different foods from all of the food groups every day. “This ensures that we receive the vitamins, minerals, energy, protein and fats we need,” Deschamps says. “The nutrients work together and have many roles to ensure our body works properly and stays healthy and strong.”
It’s a lot to think about when you sit down to a meal. Says Deschamps, “The old saying, ‘you are what you eat,’ really rings true.” 
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