In order to be used by the body, food must be broken down into molecules small enough to cross the cell membranes of the gut. This process is known as digestion. These small molecules are then absorbed into the blood and lymph.

Digestion takes place in the gastrointestinal tract, a continuous tube that extends from the mouth to the anus. The gastrointestinal tract is made up of the mouth, pharynx, esophagus, stomach, small intestine (divided into the duodenum, jejunum and ileum) and large intestine (divided into the cecum, colon and rectum). The teeth, tongue, salivary glands, liver, gallbladder and pancreas also play a part in digestion.

DigestionMuscular contractions in the wall of the gastrointestinal tract help to break down food by churning it and mixing it with the various fluids that are secreted into the gut. Digestive organs and the cells that line the tract secrete enzymes that help to break the food down chemically. Peristaltic or wave-like contractions help to propel food through the gut.

Most digestion and absorption takes place in the small intestine. Carbohydrates are mostly digested by pancreatic enzymes secreted into the small intestine. They are absorbed as single sugars, such as glucose and galactose. Protein digestion starts in the stomach and is continued by pancreatic enzymes. Proteins are absorbed as amino acids. Most fat digestion takes place in the small intestine, although some occurs in the stomach. Bile, which is secreted by the liver, and pancreatic enzymes are necessary for this process. Fats are absorbed as monoglycerides and fatty acids.

Fat soluble vitamins A, D, E and K are absorbed along with fats. Most water soluble vitamins are absorbed by diffusion. Vitamin B12 is the exception, and requires a substance known as intrinsic factor for its absorption. Some vitamins are manufactured by bacteria that live in the large intestine.

DigestionSupplements and herbs for digestion

Eating food slowly and chewing thoroughly are very important in helping to break down food properly before it enters the stomach. People who feel heavy or bloated after meals may benefit from taking digestive enzymes such as bromelain or papain. These enzymes can help to break down protein and fat in the stomach and small intestine.

Stomach acid production usually decreases with age and many people suffer symptoms such as gas, bloating and discomfort after rich meals. Betaine hydrochloride can be used in cases where stomach acid production is insufficient. Drinking a small glass of apple cider vinegar before a meal may also be useful for digestion.

Probiotics are bacteria that help to maintain a healthy balance of micro- organisms in the gut. They may be useful in those with antibiotic-induced diarrhea, yeast infections and urinary tract infections. They may also help to protect against colon cancer and the adverse effects of chemotherapy and radiotherapy. Some evidence suggests that probiotics may help to treat allergies and skin conditions, reduce high cholesterol, and improve immunity.

Flatulence is a common digestive problem. It can be a symptom of disease or may be related to an inappropriate diet and it is important to identify the cause. There are several herbal remedies that can help to ease the problem. These include sage (Salvia officinalis), peppermint (Mentha piperita), chamomile (Matricaria recutita), hops (Humulus lupulus), fennel (Foeniculum vulgare) and valerian (Valeriana officinalis).

The liver

The liver is the most important metabolic organ in the body and has fundamental effects on health and vitality. Reducing stress on the liver and helping it to heal promotes health and can help to alleviate the symptoms of many disorders. Eating a very low protein, low fat diet; avoiding alcohol, tobacco, drugs and exposure to chemical fumes; drinking plenty of water; and getting plenty of rest can help to take the load off the liver.

After the skin, the liver is the second largest organ in the body. The average adult liver weighs around 1.3 kg. Functions of the liver include:

Carbohydrate metabolism

The liver is especially important in maintaining a normal blood glucose level. When blood glucose is low, the liver breaks down glycogen to glucose and releases glucose into the bloodstream. The liver can also convert other sugars, amino acids and lactic acid to glucose. When the blood glucose level is high, just after a meal, the liver converts glucose to glycogen and to triglycerides for storage.

DigestionFat metabolism

The liver stores some triglycerides, breaks down fatty acids, and converts the breakdown products into ketone bodies. It makes lipoproteins, which are molecules that transport fatty acids, triglycerides and cholesterol to and from body cells. The liver also makes cholesterol and uses it to make bile salts.

Protein metabolism

The liver plays a role in protein synthesis. It also converts amino acids into fats and carbohydrates and converts the ammonia which results from this process into urea which is excreted in me urine.


The liver detoxifies substances such as alcohol and drugs. It can also alter or excrete some hormones.

Other functions

Other functions include excretion of bilirubin, a compound derived from the haem of worn out blood cells; the synthesis of bile salts; storage of vitamins and minerals; and activation of vitamin D.

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