CHAPTER 3
Why Do I Have IBS?
Health care providers understand the underlying cause or causes of many common medical conditions. For example, we know that elevated levels of cholesterol in the bloodstream can lead to narrowing of the coronary (heart) arteries, which may then lead to reduced blood flow to the heart and a heart attack. We know that a long history of excessive alcohol intake will damage the liver and lead to cirrhosis (scarring of the liver). Multiple research studies have found that obesity is a key factor in the development of adult onset diabetes. The medical community, however, still does not understand the precise cause, or causes, of irritable bowel syndrome. At some point, all people who have IBS ask their doctors why they developed this common condition. Many people wonder whether they were born with IBS, and others ask their doctors if they developed IBS because of something they did to themselves, such as eating the wrong foods or taking the wrong medication. Unfortunately, the precise etiology (cause) of IBS remains unknown. Given the complexity of this disorder and its multiple symptoms, it is reasonable to assume that IBS does not develop from a single cause. Rather, there are likely several factors involved in the development of IBS, and these may be different in different individuals. Data are emerging that suggest that some people are exposed to certain conditions that predispose them to develop IBS later in life.
In this chapter, I review some of the current theories about how and why IBS develops, try to address commonly asked questions about the development of IBS, and present a hypothesis for why IBS occurs in some people but not others. The following case study illustrates some of the typical issues that people face after a new diagnosis of IBS.
Susan is a 25-year-old law student. She was referred to Dr. Kaufman because of her recurrent episodes of bloating, abdominal pain, and diarrhea. Susan explained that these problems started more than six months ago with only occasional episodes of abdominal cramps; she currently has lower abdominal pain, cramping, diarrhea, and bowel urgency nearly every morning. She stated that she feels very bloated and has resorted to wearing sweat pants most of the time because other pants feel too tight. One of her friends recently joked that she looked pregnant. Her weight has been stable during this time period. Susan saw a doctor at the law school student health clinic who told her that stress was causing these symptoms and that if she eliminated caffeine from her diet and got more rest, she would feel better. Susan was frustrated by this advice because she had researched her symptoms carefully on the Internet and didn’t believe that more rest would solve her problems. During her appointment, she had asked the doctor what she thought were some simple questions, such as: “Why do I have this? Did I do something to cause this? Will it get better? And will it go away?” Unfortunately, the doctor wasn’t able to answer her questions.
Unsatisfied, Susan made an appointment with Dr. Kaufman, a specialist at a university hospital near her parents’ home in Washington, D.C. Susan told Dr. Kaufman that she has always been successful: she was at the top of her class in high school and again in college. She has a reputation for working hard and for being very competitive, whether in school or on the sports field, where she is also quite accomplished. She stated that ever since junior high school, her stomach has always been “a little twitchy.” Before exams, trips, and major athletic events, she would frequently have a lot of stomach growling and grumbling, followed by bouts of diarrhea. She attributed this to “a nervous stomach” and said that at other times, she did not have any problems with diarrhea. Susan said that her recent problems of bloating, lower abdominal pain, and urgent trips to the bathroom with loose, watery bowel movements had started nearly six months earlier. At first, she could not recall anything out of the ordinary about this time period. However, Dr. Kaufman felt that there were several important pieces of information in Susan’s history that might help answer some of her questions. He learned that Susan’s symptoms appeared to start shortly after a spring trip to Mexico. She went on the trip on the spur of the moment because she had just ended a long-term relationship with her boyfriend. The break-up was very stressful to her and she decided to join a group of her former sorority sisters on a cruise to Mexico. Unfortunately, Susan and all of her friends got sick on the trip. They each had several days of low-grade fevers, abdominal cramps, and diarrhea. Their illnesses began with nausea and vomiting, although Susan considered herself fortunate because, although she was nauseated, she did not vomit. Susan and all of her friends believed that they had food poisoning or developed some type of an infection onboard the ship. By the time they returned home, everybody felt better except for Susan. She continued to experience abdominal cramps, urgency, and diarrhea. The doctor at the student health clinic ordered some blood tests and had Susan collect samples of her diarrhea to see if there was any evidence of bacteria or parasites. All of the tests came back normal.
Dr. Kaufman carefully reviewed Susan’s medical history and could not find any information that made him especially concerned (such information is sometimes referred to as warning signs, or “red flags”; see Chapter 7). He did note that both her mother and a sister also had problems with abdominal pain, spasms, cramps, and diarrhea, although they had not been formally diagnosed with a specific disorder. His careful physical examination did not reveal anything abnormal. Dr. Kaufman told Susan that all of her symptoms were compatible with irritable bowel syndrome. He carefully explained the meaning of IBS, described the typical symptoms, and reviewed the natural history of the disease. He reassured her that her symptoms would likely improve with a combination of diet, exercise, and medications.
Dr. Kaufman then told her some surprising news. He said that she likely developed IBS because of the infection she had while in Mexico. He told her it was likely that she and all of her sorority sisters had developed some type of viral or bacterial infection of the gut (that is, a gastroenteritis). In most cases, such an infection resolves without causing any long-lasting injury, but in her case, it may have caused some persistent inflammation to the GI tract or might have injured the nerves contained within the lining of the GI tract (the enteric nervous system; see Chapter 2). Dr. Kaufman found it interesting that whereas her friends all got better, Susan did not—possibly because all of them vomited at the onset of the illness. He said that it was unfortunate that she didn’t vomit at the beginning of the illness, as this may have significantly decreased the amount of virus or bacteria to which her GI tract was exposed.
Finally, Dr. Kaufman suggested that there were three other reasons why Susan might have developed such long-lasting symptoms: (1) she had two family members with similar symptoms, which raised the issue of a genetic tendency to develop IBS; (2) she had a history of a “nervous” or “twitchy” gut and the addition of a stressful event to her system could have overwhelmed her body; and (3) some people are more susceptible to developing IBS if they are stressed at the time of an infection. Two stressors (an emotional break-up with her boyfriend and an infection in her GI tract) going on at the same time might have overwhelmed the normal defense systems in her body.
Susan asked a few more questions and then discussed treatment options with Dr. Kaufman. She felt that she now had a good grasp of the problem at hand and that some sense had been made of her symptoms and problems. She was now ready to deal with the problem of IBS.
What Causes IBS?
The etiology of an illness refers to the underlying event (or events) that cause an illness to develop. In the case of IBS, the initial event may be something simple, such as a viral or bacterial illness, which is often not even noticed or remembered by the patient. However, this precipitating incident may then lead to a cascade of events, eventually resulting in the gut dysfunction that produces the typical symptoms of IBS. In contrast to just a decade ago, the medical community now has a much better understanding of the abnormal physiologic processes that produce the symptoms associated with IBS (pain, bloating, and either constipation or diarrhea). IBS is a particularly complex disorder in which many physiological processes are involved, including abnormalities in intestinal motility (the movement of materials through the gastrointestinal tract), alterations in visceral sensory function (awareness of sensations within the GI tract), and changes in central nervous system (CNS) processing of sensory information. This relationship between the CNS and the intestinal tract has been labeled the brain-gut axis (see Chapter 2).
Although physicians may understand the physiologic processes that produce symptoms of IBS, why those processes begin in some people and not others is still unknown. Many different theories have been explored, and these are discussed below.
Genetics
A thorough medical history always includes a review of a patient’s family history. During this part of the interview, the physician focuses on medical conditions present in the patient’s first-degree relatives (mother, father, brothers, sisters), although more distant family members may be included as well. The purpose of the family medical history is to look for inherited disorders, disorders that are transmitted from one generation to the next.
Some information about the growth and development of a person is found on structures called chromosomes. Chromosomes consist of tightly coiled and compacted DNA (deoxyribonucleic acid). Specific segments of DNA make up genes, which are responsible for producing certain proteins and directing the growth and development of a person.
Every human being has 23 pairs of chromosomes. Children receive 23 chromosomes from the mother and 23 from the father: one from each parent’s 23 pairs. These include one set of chromosomes that determines a person’s sex (the X and Y chromosomes) and 22 other pairs of chromosomes, referred to as autosomal chromosomes. Autosomal chromosomes determine body characteristics such as eye color, hair type, body shape, and height. These characteristics and diseases are transmitted from parent to child in a number of distinct patterns. One of the easiest patterns to recognize is the autosomal dominant pattern (when only one of two chromosomes in a pair must have the gene present for the specific condition to develop). Some examples of autosomal dominant disorders include familial hypercholesterolemia (1 in 500 people in the United States have this disorder), polycystic kidney disease (1 in 1,250), Marfan syndrome (1 in 20,000), and Huntington’s disease (1 in 2,500).
Another common pattern of inheritance is the autosomal recessive pattern (when both chromosomes, one from each parent, have the abnormal gene, and one copy of the gene is not enough to cause the condition). Examples of autosomal recessive disorders include sickle cell anemia (1 in 625 African American people have this disease), cystic fibrosis (1 in 2,500 people), Tay-Sachs disease (1 in 3,000 people), and phenylketonuria (PKU; 1 in 10,000 people).
Many people who have IBS believe that they’ve inherited the disorder from their parents or grandparents because these family members have symptoms similar to their own. When interviewing patients and reviewing their family history, I am often told by patients that their problem must be inherited because their mother “always had bowel problems” or because their father had stomach problems “all of his life.” Although interesting, the stories of different family members and their gastrointestinal (GI) symptoms do not prove that their problems are genetically linked to a patient’s IBS. To determine whether a patient has a genetically linked disorder, the first question a physician must ask is whether that patient’s symptoms are truly similar to that of his or her family member or members. Many people lump “abdominal problems” together, such as acid reflux disease (gastroesophageal reflux disease, or GERD), ulcer disease, chronic constipation, and IBS. These individual problems likely develop as the result of separate processes, however, and should be viewed as separate medical conditions. In addition, there are many other symptoms and disorders that commonly occur in association with IBS, although they do not appear to be genetically linked.
If a patient does have first-degree relatives with symptoms of IBS, then her or his physician should make a careful note of these symptoms. However, it takes much more than just having another family member with similar symptoms to prove that a disease is genetically linked. This is especially true with a common disorder such as IBS. If two family members have Marfan syndrome, which occurs in only 1 in 20,000 people, it is probably not just a coincidence. IBS, on the other hand, is found in nearly 15 percent of the U.S. population. Thus, in a large family of seven or eight people, two family members who have IBS does not necessarily indicate a genetic link.
What do research studies show about the genetic basis of IBS? Some of the best research data about genetics come from twin studies. Twins occur in approximately 1 in 90 live births worldwide and can be one of two types: monozygotic (identical) or dizygotic (fraternal). A zygote is a fertilized egg. A monozygotic (mono means “one”) twin develops when one egg is fertilized and then splits into two identical eggs that continue to grow and develop into two genetically identical individuals. Dizygotic (di means “two”) twins develop when two different eggs are fertilized by two different sperms and hence are not identical.
If there is a strong genetic link in IBS, then researchers would expect that if IBS develops in one monozygotic, or identical, twin, it will develop in the other identical twin as well. Studies have shown that there is a statistically significant higher incidence of IBS in identical twins than in the general population. In addition, identical twins are twice as likely as fraternal twins to develop IBS. However, if one identical twin develops IBS, the incidence of the other twin developing it is not 100 percent, which it should be if the disorder is completely genetically transmitted. Many scientists who focus their research efforts on understanding IBS believe that the findings from the twin studies mean that there is a genetic predisposition for the development of IBS. This predisposition means that if a person has a specific gene (or genes), then there is an increased likelihood that he or she will develop IBS. It is unlikely that there is a single gene that predisposes people to develop IBS later in life; there may be several abnormal genes that act together to cause people to develop IBS. One theory, discussed at the end of this chapter, is that some people have a genetic factor or factors that places them at increased risk of developing IBS during their lifetime. Unless some other event or events occur, however, IBS will not develop. A genetic tendency or predisposition for IBS is not an absolute guarantee that IBS will develop.
Environment
Several research studies have shown that having a mother or father who has IBS increases the likelihood that you will develop IBS. This does not necessarily indicate a genetic link, because the risk of developing IBS is greater if your mother or father has symptoms of IBS than if you are a fraternal twin and your twin has IBS. Although there are some data that support a genetic predisposition (but not a guarantee) for the development of IBS, the comparison between the twin and parental findings raises the issue of whether the environment could also contribute to the development of IBS.
Environmental influences may include where a person lives, climate, socioeconomic status, race, religion, and the number of family members present in the household. Because behavior and personality are primarily formed during the early childhood years, is it possible that different social environments influence the likelihood of a person developing IBS later in life? This is a difficult subject to tackle because there are so many variables involved; for example, different parenting methods, educational level of the parents and the child, stability of the parents and their marriage, and the effects of schooling on the child all may have an effect on the etiology of IBS.
Despite the great prevalence of IBS, very little research has been done about environmental influences on this disease. Where one lives in the United States does not appear to affect the likelihood of developing IBS: it is just as common in the North as in the South and in urban areas as opposed to rural areas. Race does not appear to be a major factor either: IBS is as prevalent in African Americans as it is in European Americans and nearly as common in Hispanics and Asian Americans as it is in white people. In addition, studies from around the world have shown that IBS is found in a large number of people in Africa, Asia, and the Middle East. This reinforces the ideas that race, climate, and geography do not play a role in the development of IBS. To my knowledge, there are no studies that have focused solely on religion and IBS. The assumption is that because IBS is found throughout the world, in many different cultures with many different religions, then it is unlikely that religious practices play a role in the development of IBS.
Researchers currently agree that global environmental factors likely do not influence the development of IBS. On a more basic level, could individual differences at home increase the risk of developing IBS? The answer, although exceedingly difficult to measure, is quite possibly yes. How can researchers objectively measure different parenting skills and styles and compare these different styles in a standardized manner? Parenting skills may develop in response to the child’s behavior, further complicating the issue. One way to look at this would be to study differences in the prevalence of IBS during specific, contrasting time periods in our nation’s history. For example, if we knew that people were more likely to develop IBS during the Victorian era as compared to the 1960s, then some people might argue that a more rigid upbringing (popular during the Victorian era) increases the likelihood of IBS developing. Unfortunately, few such studies are available during either of these time periods, and because the research methods employed are so different, they cannot be directly compared.
We do know that parenting skills can significantly influence the development of IBS in children. IBS may develop in children because of direct influence from their parents or through more indirect influences, such as children observing that whenever their mother or father has an unpleasant task or assignment, then he or she develops abdominal pain, diarrhea, and has to stay home from work. Children model their parents quite faithfully, and before long, those children learn to have abdominal pain and diarrhea before an unpleasant assignment is due at school or work. Direct influences may be the result of parents “rewarding” their children for being ill. Staying at home because of abdominal pain may result in a reward by the parent, such as a special treat, meal, or toy (whether the illness is real or not). This reward reinforces the child’s view that being ill is desirable. Most physicians who treat people who have IBS strongly believe that parents can teach their children to develop poor coping skills and poor responses to being ill, which increase the likelihood of developing a functional bowel disorder such as IBS later on in life.
Stress
For many years, physicians told people who had IBS that the disease was caused by stress, depression, and anxiety. It was not uncommon for physicians to tell people that the symptoms of IBS were “all in their head.” The theory that stress, anxiety, and depression could cause IBS probably developed for many different reasons. First, testing at the time could not identify any organic or structural problem that could account for the multiple symptoms of IBS. Thus, if a problem could not be found, it was common practice to diagnose the patient with either a psychosomatic or a psychiatric disorder. Second, very little information was available about the brain-gut axis before the 1970s, and until 15 years ago, this concept was not widely discussed. Neither physicians nor patients were cognizant of the strong connection between the brain and the gut. Because this phenomenon was not well understood, it was difficult for physicians to account for this vital connection in their diagnostic studies or treatment plans. Finally, functional bowel disorders are a difficult concept to understand. In the past, the medical community did not really embrace this complex concept and was still operating under the rubric that the physical symptoms of IBS had to be based on some structural or biochemical abnormality that could be identified by laboratory tests or x-ray studies.
Most physicians now recognize that stress, anxiety, and depression do not cause IBS but that these emotional factors can dramatically influence the brain-gut axis. During times of emotional stress, IBS symptoms may flare up or worsen. This concept probably does not come as a surprise—we are all aware of how easily emotions affect our general well-being and state of health. For example, if your friend has a mild cold on a beautiful spring day and he has been looking forward to a planned outing for weeks, then it is very likely that he will find the mental and physical energy to go. On the other hand, if you have another friend with those same symptoms on a gray, rainy day, and she is obligated to go to some dreadfully boring meeting, you wouldn’t be surprised if she decides not to go and to stay home to nurse her cold symptoms instead. Both positive and negative emotions can greatly influence the physical state of a person. In fact, during the last decade researchers have found that positive emotions can influence the immune system in a beneficial manner.
In short, the connections between the brain and the gut are strong. The brain-gut axis is susceptible to external influences, such as stress (see Figure 3.1). In addition, internal influences such as mood and emotions (anxiety, fear, depression) can also dramatically affect the brain-gut axis. These emotions can directly influence GI activity. An example of this influence would be a lawyer who develops urgent diarrhea only before stressful court appearances.
Emotions can also modulate how the brain senses gut activity, which may be a major reason why people who have IBS have more severe symptoms when depressed or anxious. In reality, they may be having the same symptoms they normally have, but the coexisting stress (or anxiety or depression) makes it difficult for them to properly interpret the signals from their gut. Their threshold for sensing gut sensations may be lower during these stressful periods, and thus they may perceive not only more signals from the gut but also more intense signals.
Although physicians now realize that stress and anxiety do not cause IBS, when we evaluate a person who has IBS, we do let them know that they may experience a flare-up of their symptoms during times of stress. For people experiencing a flare of their typical IBS symptoms, a symptom diary may help pinpoint the stressful event (or events) that triggered the aggravation (see Chapter 13). By using a symptom diary, it is not uncommon for a person to pinpoint an event that coincided with the onset of more severe symptoms. This may be a stressful situation at home (fight with spouse, financial problems, problems with children at school) or at work (major projects, deadlines, job security). Although discussed at length in Chapter 7, pinpointing a triggering event is critical in the overall IBS treatment plan, which involves treating the coexisting life stressors along with the IBS symptoms. Until these coexisting stressors are treated and under control, they will continue to negatively affect the brain-gut axis and make symptoms worse—and they may actually increase the likelihood of developing IBS in the first place (see below and Figure 3.1).
Diet
The topic of diet is usually raised by people who have IBS because eating so often produces symptoms of bloating, gas, abdominal pain, or even diarrhea. Many people think that different foods seem to cause IBS symptoms. Certainly, many people who have IBS develop a worsening of their symptoms after eating; however, this is probably just an exaggerated physiologic response to eating (see Chapter 6). Some people who have IBS may be intolerant of certain foods, especially lactose and fructose, and these can produce symptoms that mimic IBS. Celiac disease (an allergy to wheat) can cause symptoms of gas, bloating, and diarrhea and therefore resembles IBS (see Chapter 10). Other food allergies rarely produce symptoms that mimic IBS, but they may worsen IBS symptoms (see Chapter 15). True food allergies are uncommon, but IBS is quite common. At present, there are no good data to support the view that any particular diet causes IBS. However, as noted in the treatment section of this book (see Part III and particularly Chapter 15), there is some good evidence that specific diets may improve IBS symptoms in some people.
Figure 3.1. Contributing Factors in the Development of IBS
Although the precise mechanism that leads to the development of IBS remains unknown, this diagram illustrates likely influences in a sequence. Research studies have shown that some people have a genetic predisposition to develop IBS. This predisposition is not a guarantee that IBS will develop, but it does increase the likelihood that IBS will occur. One theory is that, for IBS to develop, a second or third inciting factor needs to be present as well. For example, a common infection of the GI tract early in life (such as a “stomach flu”) followed by a period of stress might produce the right setting for IBS to develop.
Medications
Medications may be over the counter, prescription, herbal, homeopathic, allopathic, or naturopathic. Their goal is to treat a specific problem as effectively as possible while producing as few side effects as possible. Unfortunately, practically all medications have side effects. Some side effects are more severe than others, but no medication is without risk. The power of medication is so strong that in some research studies even a placebo (a “sugar” pill) produces side effects in some people. A common opinion in the medical community is that if aspirin were a new medication and was brought before the Food and Drug Administration (FDA) for approval now, it would never be approved because of the large number of known side effects. But hasn’t aspirin been shown to have many benefits, and isn’t it sold all over the world? As you can see, the topic of medications and side effects is extremely complicated.
Some types of medications used for other medical problems may produce side effects that mimic symptoms of IBS, and other medications may worsen the symptoms of IBS. Medications used to treat constipation (lactulose and sorbitol) may produce significant bloating. People with chronic pain are often prescribed narcotics, which slow down the normal movement of gut contents (called peristalsis) and frequently lead to constipation. People with migraine headaches or chronic functional GI pain may be prescribed a tricyclic antidepressant (TCA), commonly used to treat chronic nerve pain and sometimes very effective in the treatment of IBS (see Chapter 17). However, in some people who take a TCA, increased dosage can cause constipation. At present, there are no good data available to suggest that any specific medication causes IBS.
Infectious Illnesses
Several research studies have shown that an infectious gastroenteritis (an inflammation of the lining of the stomach and intestine) can increase the likelihood of a person developing IBS later in life. Everyone has friends, relatives, or neighbors who developed an infectious gastroenteritis (often labeled “traveler’s diarrhea” or “tourista”) while on a trip abroad. Although most recover completely, some people with infectious gastroenteritis continue to have persistent symptoms of bloating, abdominal pain, and altered bowel habits for months or even years after the acute illness. These people typically undergo blood work, specialized stool studies, and even procedures such as colonoscopy or a computed tomography (CT) scan in an attempt to diagnose the problem. By the time they see a physician, the active infection has usually gone away, but their symptoms continue—a medical condition known as post-infectious IBS. Although the precise mechanism is unknown, researchers have several theories as to why IBS may persist after an acute episode of infectious gastroenteritis. For example, the infection may temporarily or permanently injure the nerve supply within the GI tract that is responsible for coordinating the movement of contents in the gastrointestinal tract (peristalsis). Injury to the nerves could lead to either diarrhea or constipation and may also lead to increased abdominal pain and an increased awareness of pain in the GI tract (called visceral hypersensitivity). Another possible reason why IBS persists after infectious gastroenteritis is immune hypersensitivity, whereby recurrent exposure to a previously benign substance causes an inflammatory state in the GI tract. This persistent state of inflammation could then alter intestinal motility and lead to diarrhea.
In one of the most telling examples of post-infectious IBS, a large number of people in a small town in Canada developed severe gastroenteritis after the town water supply was contaminated with runoff from local farms. Many people were hospitalized and treated with antibiotics for their infectious gastroenteritis. Several people died, including one of the town’s doctors. Two years later, nearly one-third of the townspeople had developed symptoms of IBS, and nearly 10 years after the outbreak, more than one-third of the population continued to have symptoms of IBS, although they did not have these symptoms before the outbreak of gastroenteritis.
Abuse
During the last decade, many published scientific studies have explored the role that a history of previous physical, emotional, or sexual abuse plays in the development of IBS. Studies revealed a higher incidence of physical or sexual abuse in people (primarily women) who have IBS than in control groups of people who do not have IBS. This difference may be a result of self-selection (people with histories of abuse are more likely to seek health care), increased severity of symptoms, high levels of psychological distress, or poor coping skills. Physicians at academic medical centers and large university hospitals tend to see a significantly larger population of people who have IBS and report a history of sexual or physical abuse than physicians in community practice settings. Clearly, a history of abuse is an important factor to consider in people with functional bowel disorders. A person’s decision of when to discuss abuse with a doctor is a highly personal one, but he or she should definitely mention the abuse, because it is a vital piece of information that may lead to a major change in the overall treatment plan.
One cautionary note: if you have been abused and decide to discuss this issue with your doctor, make sure there is adequate time for an appropriate discussion. This emotionally charged issue should not be brought up as you are leaving the office with coat on and hat in hand.
How Does IBS Develop?
Although there are many different theories about why some people develop IBS and others do not, the information presented throughout this chapter allows us to diagram a proposed pathway for the development of IBS. A common starting point is the genetic predisposition to develop IBS, which probably involves the interaction of multiple genes (not just the actions of a single gene). Genetic predisposition is not a guarantee that a person will develop IBS, but it does increase the likelihood for her or him.
If a person is genetically predisposed to develop IBS, he or she should be aware of the following factors that may increase the likelihood of developing the disease: significant stress, an infection in the GI tract, a history of abuse (emotional, physical, or sexual), and environmental and parental influences. The precise role that each of these factors plays in the development of IBS is unknown. In addition, there are other factors that explain why some people who have IBS develop more severe symptoms than others. I discuss these other factors throughout the book.
Summary
• We do not know why IBS develops in some individuals but not others.
• IBS probably develops as a result of many different factors (see Figure 3.1).
• Certain individuals may be genetically predisposed to develop IBS. It is not guaranteed that these individuals will develop IBS, but their genetic predisposition increases the likelihood.
• There is no good evidence that a specific diet or type of medication can cause IBS.