Fundamentals of Human Nutrition/Gut health

3.4 Gut HealthEdit

3.4.1 Cellular turnoverEdit

Dietary fiber, most commonly found in plant materials such as fruits, vegetables, seeds, nuts, legumes, whole grains, and bran, is a very important part of maintaining gut health. Fiber, also referred to as “roughage” or “bulk”, contains components that cannot be digested by the human intestine. Adding fiber to your diet allows your gastrointestinal tract to essentially be exfoliated, increasing intestinal cellular turnover (Valhouny, 1985). Just like other tissues in the human body that are sloughed off and regenerated, the inner gastrointestinal cells are no different. This “sloughing off” allows for a larger bulky stool that can carry impurities out with it like a sponge.

Research has shown that fiber is associated with decreased risks for certain chronic diseases such as coronary heart disease, diabetes, obesity, hypertension, stroke, and gastrointestinal disorders (Anderson, 2009). Increasing your intake of fiber can also lower blood pressure, promote regularity, help immune function, stabilize blood glucose, and also aid with weight loss.

Unfortunately, most Americans consume less than half of the recommended amount of daily fiber (Anderson, 2009). Experts warn that it is not recommended to drastically increase your fiber intake because this might induce gastrointestinal upset, such as bloating, diarrhea, and gas. Instead, it is recommended to gradually increase your intake of fiber so your gut has time to adjust. A simple trick experts recommend in order to increase your fiber intake throughout the day is to remember to eat the skin of the fruits and vegetables you consume (instead of peeling it off), eat fruits and vegetables raw (instead of steaming or cooking them), and by adding bran to your diet whenever possible.

Dietary fiber comes in two forms – soluble and insoluble. Both of these forms have different purposes for different stages of digestion. Most fiber-rich foods contain both of these forms, but normally a higher proportion of one than the other (“Fiber”, 2014). Soluble fiber absorbs water and will turn into a gel-like material, while insoluble fiber cannot absorb water. Soluble fiber slows digestion through the small intestine, causing a more satiated feeling. This can be helpful for individuals attempting to maintain a healthy weight or even lose weight. Research has also shown that soluble fiber can prevent heart disease by essentially soaking up cholesterol as the digestion process progresses. Soluble fibers can also act as a prebiotic that improves the microflora of the intestine. Insoluble fiber speeds up the elimination of waste products in the gastrointestinal tract. This promotes regularity and can increase the amount of fecal matter excreted.

3.4.2 Intestinal bacteriaEdit

The human microbiome is defined as the collection of microbes found in or on the human body; microbes is defined as microscopically small organisms including bacteria, viruses, fungi, and protozoa (Whitney & Rolfes, 2013). The microbiome aids in the protection against infection and inflammation, and maintains mucosal homeostasis and immune health. It also regulates the development of epithelial tissue in the intestine, and is involved in the absorption of nutrients and the digestion of food. The Microflora is known as the non-disease-causing bacteria that lies in the large intestine and carries out various functions in the microbiome. Functions of the Microflora include the digestion of fiber; the metabolism of carbohydrates, lipids and other compounds; and the production of vitamins K and B12 (Gorbach, 1996). A healthy GI tract has a collection of over 100 trillion microbes, and bacteria includes over 400 different types of these microbes (Whitney & Rolfes, 2013). A person’s diet greatly affects GI health, and having a healthy gut promotes proper digestion and protection against disease. The microbiome consists of good and bad bacteria which are responsible for carrying out these functions.

Good Bacteria:

Good bacteria consist of probiotics, such as Lactobacillus and Bifidobacterium bifidum. Probiotics keep the microbiome healthy, aid in digestion, and improve overall health. Some foods that contain probiotics are yogurts, juices, fermented and unfermented milk, sauerkraut, and pickles (“Probiotics,” 2015). Since antibiotics kill off all of the bacteria in the gut, it is often recommended to eat yogurt while taking antibiotics in order to regain some probiotics that were lost. Prebiotics also work in keeping the intestine and microbiome healthy. Prebiotics are carbohydrates that feed the good bacteria and are unable to be digested. Examples of foods that contain prebiotics include wheat, artichokes, asparagus, bananas, and onions (“Probiotics and Prebiotics,” 2015).

Bad Bacteria:

Bacteria that are known to be disease-causing are referred to as pathogens, or “bad” bacteria. Bad bacteria consist of Bacteroides, E. coli, Clostridium difficile, Enterococcus, and more. Bacteroides are the most abundant bacteria in the intestine, and are some of the most resistant bacteria to antibiotics (Wexler, 2007). Bacteroides aid in carbohydrate metabolism, are anaerobic and bile-resistant, can adapt easily to changes in the environment, and have mutualistic relationships with the human body when retained in the gut (Wexler, 2007). Once the bacteria escape the gut, they can cause severe illness and disease. Pathogenic bacteria have shown to contribute to a variety of diseases, such as inflammatory bowel disease (IBD), colon cancer, Chron’s disease, diabetes, colitis, and obesity.


Intestinal bacteria are important for producing enzymes and regulating various substances in the gut. Bacteria specifically synthesize vitamin K, biotin, vitamin B12, vitamin B6, folic acid, riboflavin, thiamine, and pantothenic acid (Whitney & Rolfes, 2013). The bacteria are also responsible for breaking down bile acids, and are able to mediate metabolic effects by producing short-chain fatty acids. Proteins are later broken down into amino acids and peptides, and then fermentation occurs (Blaut & Clavel, 2007). Depending on a person’s diet, the intestinal bacteria can become altered, which can cause changes in metabolism.


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Whitney, E., & Rolfes, S. (2013). Digestion, Absorption, and Transport. In Understanding Nutrition (14th ed.). Wadsworth, Cengage Learning.

3.4.3 Problems in digestion and absorptionEdit

Gastroesophageal Reflux Disease (GERD)

Gastro esophageal reflux disease (GERD), commonly known as acid reflux or heartburn is a painful sensation a person feels behind the breastbone when the lower esophageal sphincter allows the stomach contents to reflux into the esophagus. Normally, a person's diaphragm will close so nothing goes back to the esophagus but over time, the diaphragm becomes weaker around the esophagus and can eventually form a hole called the hiatus. If this hole is large enough it can form a hiatal hernia which is when the diaphragm is no longer reinforcing the valve. Acid reflux can happen when a person eats or drinks too much, if he/she is wearing tight clothing, changes position (laying down), or some medications and smoking can cause it. Weight gain can increase the frequency, severity and duration of heartburn symptoms. Treatment is fairly simple for heartburn not caused by an anatomical defect. Simple changes such as chewing food more thoroughly, eating slower or eating less at one sitting are all strategies to avoid heartburn. Over-the-counter antacids and acid controllers may also provide relief but should not be used frequently as this may cause problems.

Irritable bowel disease

Irritable bowel disease is an intestinal disorder of unknown cause, however researchers are actively investigating the nervous system's role. It is one of the most common GI disorders, characterized by frequent or severe abdominal discomfort. Diarrhea, constipation, or alternating diarrhea and constipation can also occur as a result of Irritable Bowel Syndrome. In most cases, GI contractions are stronger and last longer than normal, forcing intestinal contents through quickly and causing gas, bloating and diarrhea. However, sometimes the opposite can occur where the GI contractions are weaker than normal causing constipation. Triggers such as eating certain foods or stress can aggravate symptoms but not cause them. Treatment for this disease include avoiding individual foods that aggravate one's symptoms and eating smaller meals. In addition, peppermint oil and antispasmodic drugs may also be effective as treatment.

Food intolerance: Lactose Intolerance

Lactose Intolerance is a very common intolerance where intestinal cells do not produce enough of the enzyme lactase. Lactase is needed to be able to digest and absorb lactose efficiently. In healthy individuals, lactase will break down lactose into galactose and glucose, then they will be absorbed through the lining of the intestine. People with lactose intolerance do not have enough of the enzyme lactose in the bloodstream, thus undigested lactose will sit in the gut. After a little while bacteria will begin to break down the lactose, this will cause cramping, diarrhea and gas to build up in the gut.

Symptoms are usually caused within 30 minutes to 2 hours after lactose is ingested, with common symptoms including abdominal pain, bloating and diarrhea. With a lactose intolerance the undigested lactose becomes an energy source for intestinal bacteria, causing disturbances in intestinal motility and abdominal discomfort (Bhatnagar and Aggarwal,2007). The severity of symptoms depends on many factors such as how fast the lactose reaches the intestinal mucosa or the rate of gastric emptying (the slower the emptying the more time the body has to try to break down the lactose). Many of these symptoms sound awfully similar to symptoms that people suffering from Irritable Bowel Syndrome experience. As of today there have been many studies looking at the link between lactose intolerance and IBS. (Davis, n.d.)

There are four types of lactase deficiencies. There is the primary lactase deficiency, this deficiency is autosomal recessive and can develop throughout the various stages of life. Next is secondary lactase deficiency, this occurs after there has been damage to the intestinal mucosa or intestinal bacteria. Thirdly, there is congenital lactase deficiency, this deficiency occurs in infants and is very rare. It occurs when infants cannot break down lactose whatsoever whether in breast milk or formula. If left untreated infants can suffer from severe dehydration and weight loss (Genetics Home Reference, May 2010). Lastly, developmental lactase deficiency his deficiency occurs when a baby is born premature. This is because the production of lactase only occurs when a fetus is at 34 weeks.

Currently, there is no single diagnostic test that is agreed upon, but there are many different types that can be used when appropriate. (Mattar, R. (n.d.). Firstly there is the lactose tolerance test; this test begins with patients being giving 2g of lactose per kg of body weight on an empty stomach. Then glucose levels will be tested in the blood, if there is a rise in glucose levels by 1.11 mmol/L or larger after 60–120 minutes after ingestion, then you will be diagnosed with a lactose intolerance. Secondly, there is the breath hydrogen test; this involves measuring the concentration of hydrogen when an individual exhales. This is due to the fermentation of bacteria in the small intestine. If hydrogen levels increase more than 20 ppm then you are diagnosed with the intolerance. Lastly, there are genetic tests available to see if you have the intolerance, however these tests cannot test for all genetic mutations.

Managing your intolerance requires dietary changes; this does not mean elimination of all dairies. Many people with the intolerance can consume up to 6g of lactose without disturbances. Usually products such as yogurt can be consumed as well. This is due to the bacteria in the yogurt that can digest the lactose itself. People who choose to consume no milk products need to carefully plan their diet, as they run risk for not meeting their vitamin D, claim and riboflavin needs.

Celiac Disease

Celiac Disease (CD) has become very common and people are being diagnosed with this illness more and more every day. More than 2 million people in the U.S. have this disease, that’s 1 in 133 people. CD is a disease that slowly damages the inside lining of the small intestine (see fig. 1). By doing this it interferes with the normal absorption of nutrients from food. People with CD actually have an allergy to a protein called gluten, which is found in many foods. This protein can be found in wheat, rye, oat, and barley. However, when consumed by a CD patient, the body reacts with an adverse reaction by destroying the villi, which are tiny hair like projections on the inner lining of the small intestine. Villi are normally responsible for the absorption of nutrients through the wall of the small intestine directly into the blood stream. If the villi are damaged, a person becomes malnourished, not getting the nutrients the body needs. CD is genetic, but is usually triggered after things like surgery, pregnancy, viral infections, or even severe emotional stress.

Symptoms of this disease vary tremendously. Some people can develop all symptoms, while others, don’t have any at all. These symptoms can occur within the digestive system and in other parts of the body. The most common are digestive symptoms which include: abdominal pain and bloating, diarrhea, nausea and vomiting, constipation, weight loss, and pale, foul-smelling, or fatty stool. These digestive symptoms are more common in children with CD. Adults experience other symptoms including: iron-deficiency anemia, fatigue, bone or joint pain, arthritis, bone loss or osteoporosis, depression or anxiety, tingling numbness in hands and feet, seizures, missed menstrual periods, infertility or miscarriages, canker sores inside mouth, and an itchy skin rash called dermatitis herpetiformis.

There’s only one treatment for CD, and that’s maintaining a gluten-free diet for the rest of your life. A diet without gluten will prevent further damage to the villi on the inner lining of the small intestine and prevent malnutrition. Patients with newly diagnosed CD are usually sent to a dietitian to learn how to start a gluten-free diet plan. This diet will stop the symptoms and heal existing damage, meaning a person will eventually be able to absorb nutrients from food normally. A gluten-free diet generally means not to consume any food with gluten ingredients; this eliminates wheat, rye, oats, and barley. The most common foods with these ingredients include: bread, pasta, cereal, crackers, baked goods (anything with enriched flour), and some processed foods. Some foods that CD patients are allowed to eat include: potato, rice, soy, quinoa, “plain” meats, fish, fruits, and vegetables. When grocery shopping CD patients should read food labels, this is where all the ingredients of the food are listed. Even things that you wouldn’t expect to have gluten, just might, including vitamins and medications.

Diverticulosis and Diverticulitis

Diverticulosis is a condition that occurs when the body is deprived of fiber. This condition most commonly occurs in the sigmoid colon and results in the formation of sacs called diverticula, which are herniations of the mucosa, that form along the colon wall. The lack of fiber causes the contents of the colon to diminish in size and ultimately the result is that colon is forced to exert a higher pressure on the walls. Over time this pressure can produce diverticula and in extreme cases of diverticulosis a similar condition called diverticulitis can occur which is considered to be a more serious condition.

Diverticulitis is the result of the inflammation of the diverticula. One of the most effective ways to reduce the chance of developing diverticulitis from diverticulosis is through increasing the amount of fiber intake that one is receiving. Previously people with diverticulosis were told to avoid nuts, seeds, and popcorn because it was believed to irritate the walls of the colon. However, this information has not been scientifically proven and there are currently no known specific foods that are known to cause the formation of diverticula. However, it is recommended that someone with diverticulosis eat foods high in fiber such as fruit and vegetables. Consuming foods that are rich in fiber will ultimately soften the stool and cause it to pass through the body smoothly therefore reducing the amount of stress and pressure inside the walls of the colon. Some physicians recommend a liquid diet, however, in order to reduce stress to the colon wall and ultimately foods that pass through the colon with ease are considered advantageous in the case of diverticulosis. Some of the risk factors that are involved in forming diverticulosis is smoking and obesity.

If diverticulitis increases in severity it can lead to diverticula that may burst and leak feces into the abdominal cavity. Eventual surgery may even be required and certain parts of the colon, such as the sigmoid colon, may need to be removed. Diverticulosis is considered a relatively common disease and is frequently discovered through routine colonoscopies. 30% to 40% of all Americans over the age of 50 have been diagnosed with diverticulosis and over half of adult Americans over the age of 70 are eventually diagnosed with diverticulosis. Diverticulitis is a lot less common and only occurs in about 20% of diverticulosis patients. However, if improper colon care and fiber intake is not considered, the chance of developing diverticulitis is considered to be much greater.


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