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The gastrointestinal system is the portal through which nutritive substances, vitamins, minerals, and fluids enter the body. Proteins, fats, and complex carbohydrates are broken down into absorbable units, mainly in the small intestine.

The digestive system introduction

The products of digestion and the vitamins, minerals and water cross the mucosa and enter the lymph or the blood. Food digestion is the physical and chemical breakdown of food into forms that can be used by the body’s cells.  Food digestion begins in the mouth when a bite of food is chewed. The main function of the gastrointestinal tract is to digest and absorb nutrients, and it is variously adapted for this. Taste provides a guide to the nutritional value or potential toxicity of food.

The alimentary tract extends from mouth to anus. It consists of esophagus, stomach, small intestine and large intestine. The small intestine is divided in to duodenum, jejunum and ileum. The large intestine is divided in to colon, rectum and anal canal. The process of digestion starts in the mouth itself and most of the nutrients get absorbed in the small intestine. The colon is mainly involved in the conservation of water and electrolytes.

Major nutrients

Food items are divided in to energy yielding foods (carbohydrates and fats) and body building foods (proteins) and protective foods (vitamins and minerals). Carbohydrates, proteins and fat are called major nutrients. Starches, sugars, milk, cereals, roots and tubers provide carbohydrates. About 50-55% of the total calories is derived from carbohydrates. Proteins are derived from both animal sources like meat, eggs, fish and vegetable sources like pulses, cereals. About 10-15% of the total calories is derived from proteins. Fats are derived from animal sources like cheese, egg, meat, fish and vegetable sources like groundnut, mustard. Small quantities of fat called invisible fat are derived from other foods such as cereals, pulses, nuts and vegetables. About 25-30% of the total calories is derived from fats.  Carbohydrate and proteins yield 4 calories per gram and fat yields 9 calories per gram.


Vitamins and minerals are called the micronutrients. They are called micronutrients because they are required in small amounts which may vary from a fraction of a milligram to several grams. Any nutrient whose recommended dietary allowance is less than 100 mg per day is called a micronutrient.


Enzymes are the most critical element of digestion. They break down complex nutrients in to simpler substances and facilitate their absorption.

Digestion of carbohydrates

Carbohydrates are ingested as starches and sugars. They are acted upon by enzymes like amylase and oligosaccharidase and are broken down in to simpler substances. In the small intestine they are further broken down in to units like glucose, galactose and fructose by enzymes called as disaccharidases. These units called monomers are then absorbed in the small intestine.

Digestion of proteins

Protein digestion starts in the stomach where it is acted upon by pepsin. Digestion of protein continues in the small intestine with the enzymes like trypsin, endopeptidase and exopeptidase which break down protein in to simpler units.  Proteins are broken down in to amino acids and are absorbed in the small intestine.

Digestion of fats

Digestion of fat mainly occurs in the small intestine. Since fats are not water soluble, they are emulsified first. Digestion of fat needs the presence of bile salts which are present in the bile secreted by liver. The enzymes lipase, phospholipase and cholesterol esterase breakdown fats in to simpler units like fatty acids and cholesterol which get absorbed in the small intestine.

Digestion of vitamins and minerals

Water soluble vitamins include B complex vitamins and vitamin C. These get absorbed in the small intestine. Fat soluble vitamins include Vitamin A, D E and K. These need the presence of bile in the small intestine for absorption. Minerals are all absorbed in the small intestine.

How to improve your digestive system?

The following are some of the important steps that should be followed to improve your digestive system:

  • Chewing well while eating – One should chew well while eating. During chewing food is broken down in to smaller chunks. Moreover digestion of carbohydrates starts in the mouth itself. Saliva contains the enzyme amylase which initiates the process of digestion of carbohydrates.
  • Diet should include high fiber food items. Fiber in the form of cereals, whole grains, and fresh fruits and vegetables should be taken. These fibers flush out the waste products from the body.  Diet deficient in fiber can lead to various health problems like constipation, diverticulosis and formation of polyps in the colon. 15-25 grams of fiber per day is recommended.
  • Drinking plenty of water – Water along with fiber prevents constipation
  • Avoiding processed food and fast food – These should be avoided as they are not nutritious enough and are not balanced.
  • Enriching gut flora – Diet containing yogurt provide good bacteria. Gut bacteria improves your digestive system. They prevent gut infection and also are helpful in the relief of irritable bowel syndrome.
  • Spicy food should be avoided if a person is having acid peptic disease.
  • Fatty food should be avoided if a person is having gallbladder disease.
  • Exercise is recommended to improve your digestive system. Exercise controls appetite, it helps in food digestion, burns calories, controls blood sugar, relieves stress which is a risk factor for irritable bowel syndrome and also relieves constipation. The recommended physical activities are   swimming, walking and cycling.

Foods that is recommendable for better digestion

Although the body needs nutrients from a wide variety of foods, it does not need them in all the same amounts. A well balanced diet is recommended for better digestion and good health. The diet should contain proteins, vegetables, fruits, whole grains and some amount of unsaturated fat. Improper nutrition can lead to obesity. According to the World Health Organization (WHO), obesity has become a worldwide problem that has significant effects on health.

In 1992 nutrition recommendation in the form of the Food Guide Pyramid was released. The Harvard University has made some changes in it and developed an alternative food pyramid called Healthy Eating Pyramid.

The healthy eating pyramid recommends the following:

  • Daily exercise and weight control
  • One should eat more of the food items that are present in the base of the pyramid and less of the food items that are in the apex of the pyramid.
  • More of whole grains, fruits, vegetables and healthy fats and oil should be taken. Whole grains could be oatmeal, whole wheat bread and brown rice. Healthy unsaturated fats include olive, canola, soy, corn, sunflower, peanut, trans fat-free margarines
  • Nuts, seeds, fish, poultry and eggs should be limited when compared to whole grains and vegetables and fruits.
  • One to two servings of dairy is recommended
  • Red meat, butter and refined grains should be taken sparingly. Refined grains include white bread, rice and pasta.  Potatoes, sugary drinks, sweets and salt should also be used sparingly.
  • Multivitamin supplements and extra vitamin D should be taken daily
  • Alcohol in moderation is optional.

  • The Gastrointestinal System at a glance – Satish Keshav
  • Digestion and Nutrition – Robert Sullivan