What are stools?
Stools are digested and metabolized byproducts of the body excreted from the bowels as wastes . These fecal materials are also termed as feces, faex in Latin, poop, poo, number two and doodoo .
Stool Transit TimeThe total time it will take the food to be eaten until it is eliminated and excreted as stools is estimated to be 40 hours for adults and 33 hours for children [3, 4, 5]. However, this can vary from person to person, based on the bowel function. Hence, in humans, bowel movement and subsequent fecal excretion may occur from as frequent as once to thrice a day to as seldom as once every 3 days .
Simply put, constipation is infrequent passage and production of dry and hard fecal material, while diarrhea is frequent evacuation of watery stools. 
An illustration showing stool transit time, which is around 40 hours in adults and 33 hours in children.
Types of StoolDeveloped by the University of Bristol in 1997, the Bristol (also known as Meyers) Stool Scale was formulated to categorize stools according to its form. This is said to be mainly influenced by the amount of time the fetal material spent in the colon, the stool transit time. [8, 9]
The types of stools include: separate hard lumps; lumpy sausage-shaped; sausage-shaped with cracks; soft, smooth and snakelike; soft blobs with well-defined edges; fluffy, mushy stools; and entirely liquid stools. 
This image describes the types of stools as developed by the University of Bristol.
What Comprises Feces?Feces are mainly composed of water, which is approximately 75%. The remaining 25% is made up of solid particles, and is subdivided into the following: 30% indigestible food matter such as cellulose, 10 to 20% cholesterol and fats, 10% calcium and iron phosphates, and 2 to 3% protein. 
Alterations in Stool CompositionThe fecal composition, however, may vary depending on length of time the fecal materials stay in the intestinal tracts. The gut absorbs water from the stool; thus, defecating more often will mean having stools with more water and retaining feces will mean passing out stools with less amount out of water. 
These changes are also influenced by one’s diet and health. One major representation of fecal composition modification is the presence of undigested food in stools, which would be this article’s main focus.
Undigested Food in Stools: Can This Be Normal?Undigested food can normally be encountered in the feces. In fact, 30 % of feces are composed of indigestible food matter . This percentage, however, cannot be grossly observed.
These indigestible foods often contain high amounts of fiber. These fibers cannot be digested by the human intestinal tract due to lack of enzymes and its resistance to hydrolysis. They are excreted from the body unchanged, some are metabolized to gas and acids. Examples of food rich in these fibers are corn, carrots, peanuts and cereals. 
Too Much of a Thing Can Also Be BadWith levels of indigestible food higher than 30%, undigested food particles can be seen visibly in the fecal matter. With this, a number of reasons can be considered.
Irritable Bowel SyndromeThis is an array of abdominal symptoms with still an unknown etiology. Symptoms of which include abdominal cramps, alternating bouts of diarrhea and constipation, bloating, distention, and the presence of mucus and undigested food particles in the stool. [11, 12]
Acute Gastroenteritis/DiarrheaAcute gastroenteritis has loose bowel movement, or diarrhea, as its main symptom. Other manifestations include abdominal pain, loose watery stools, nausea, and vomiting. The illness is considered to be more severe when weight loss, fever, and undigested food in stools are present. The disease can either be a self-resolving viral illness or an antibiotic-requiring bacterial infection. 
Toddler’s DiarrheaThe term pertains to chronic diarrhea in young children, between ages of 1 to 5 years. With an unknown cause, this type of diarrhea is not from malabsorption nor food intolerance. Affected toddlers have three of more episodes of watery stools per day. The said stools are often foul smelling and have undigested food particles in them. 
Malabsorption (e.g. Celiac Disease)This is the inability to absorb food, particularly sugar, fats, proteins and vitamins. It is usually due to injury of the intestinal lining, and abnormal production of hydrochloric acid. Aside from having undigested food particles in the stools, patients with this condition may also have abdominal cramps, flatulence, loose stools and weight loss. 
What Else Is There: Other Signs and SymptomsOther clinical manifestations can observed in the presence of undigested food particles in stools. These are as follows: [11, 12, 13]
- Abdominal pain
- Presence of loose, watery stools
- Vomiting and nausea
- Fever (if with dehydration and/or infection)
- Loss of appetite
- Anxiety and depression
- Sleep disturbance
- Easy fatiguability
- Sensation of incomplete evacuation
- Urgency in defecating
- Difficulty of initiation of Bowel Movement
If any of these symptoms would be present, consult to the doctor for prompt evaluation must be done.
What To Do Next?No single diagnostic test can be done to immediately ascertain the diagnosis. A thorough and complete history and physical examination must be done. History should include food and drug intake, presence of weight loss and previous history of changing bowel movement. Physical examination should not only focus on the abdomen, but on all the systems of the human body, including the anus and rectum.
Laboratory examinations useful in the diagnosis include complete blood count to rule out the presence of anemia, and stool analysis and culture to identify infection.
Other diagnostics for confirmation of illness are ultrasonography of the whole abdomen, barium studies and the scopes (gastroscopy and colonoscopy). [12, 15, 16]
The Proper ManagementUnless diagnosed by the physician, no particular medication should be given, but proper hydration and supplementation. The following statements must be remembered.
- Encourage oral fluid intake to around two to three liters per days
- Volume per volume replacement of losses should be done, if possible.
- Consume foods with low fiber: rice, grapefruits, bananas, apples, chicken, ground beef, fish, cottage cheese.
- Foods with grease and fats, whole grains, raw fruits and vegetables, and strong spices should be avoided
- Avoidance of gas-forming foods: beer, cabbage, beer, carbonated drinks is recommended
- Intake of probiotics and foods such as yogurt is advised
- Try to limit caffeinated beverages
Warning SignsPrompt consult or follow up with physician should be done when certain manifestations are noted: dark colored urine, decreased quantity of urine, dry and flushed skin, irritability and confusion. These are signs of dehydration, which if neglected, may be fatal. 
- Picco, M. Digestion: How Long Does It Take? http://www.mayoclinic.com
- Metcalf, A. et al. Simplified Assessment of Segmental Colonic Transit. Gastroenterology. 1987; 92:40
- Weaver, L. et al. The Bowel Habits of Young Children. Archives of Disease In Childhood. 1984; 59: 649.
- Lewis, SJ. Et al. Stool Form As A Useful Guide to Intestinal Transit Time. Scandinavian Journal of Gastroenterology. 1997; 32 (9): 920-4
- Constipation Management and Nurse Prescribing: The Importance of Developing A Concordant Approach. http://www.constipationadvice.co.uk