For most people, FODMAPs are harmless or possibly beneficial carbohydrates that feed the bacteria in our guts. For people with IBS, they can spell hours of pain, bloating, and frantic trips to the bathroom. Could the low FODMAP diet be the solution? Read on to find out.
What are FODMAPs?
FODMAPs are a group of carbohydrates which, in the last decade or so, have been identified as the prime suspects behind irritable bowel syndrome, or IBS. FODMAPs is a catchy acronym that stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols [1, 2, 3].
- Fructans and galactans
- Galacto-oligosaccharides (GAS)
- Polyols (sugar alcohols, or any sweetener that ends with -ol)
Beneficial Effects in Healthy People
The major products of FODMAP fermentation are short-chain fatty acids (SCFAs), including butyrate. These nutrients feed the cells of the intestinal wall, lower intestinal pH, and strengthen the gut barrier. As intestinal pH decreases, so do the populations of Enterobacteria and Clostridia, widely considered “bad” bacteria [7, 4, 8].
For most people, then, FODMAPs should be beneficial. So what makes them harmful to some people?
Dangers in People with IBS
Despite their potential benefits, FODMAPs seem to produce (or at least worsen) symptoms in people with irritable bowel syndrome, or IBS. IBS is a digestive disorder that causes abdominal pain, gas, bloating, and poor stool quality (either diarrhea or constipation). IBS is very rare in some parts of the world (1.1% in France and Iran) and common in others (35.5% in Mexico) [11, 12].
Most doctors now agree that IBS is caused by disordered communication between the gut and the brain. However, certain foods – especially those containing FODMAPs – trigger symptoms more consistently than others .
Normally, the wall of the intestine forms a physical and immune barrier between the intestine and the bloodstream. This barrier allows nutrients to pass through; it also keeps water and electrolytes in the blood and harmful bacteria and substances out .
FODMAPs disrupt the barrier between the intestine and the bloodstream in people with IBS. This allows other harmful agents, such as bacteria and inflammatory proteins, to pass through and cause damage. Fructose may be the worst offender when it comes to increasing intestinal permeability [14, 15, 16, 9].
According to one study, many people who believe that they have gluten intolerance may actually be intolerant to fructans. 59 people who believed that they were gluten intolerant, but did not have celiac disease, ate one granola bar per day. For one week, the bar contained gluten; for one week, the bar contained fructans; for one week, the bar was a placebo that contained neither .
24 participants had their worst symptoms when eating the fructan bar, 13 responded worst to the gluten bar, and 22 experienced the worst reaction from the placebo. However, the researchers acknowledged that the combined effect of fructan and gluten may be worse than either alone .
Some researchers estimate that around 24% of people with IBS may blame fructans for the worst of their symptoms .
What is a Low FODMAP Diet?
- Improves symptoms of IBS
- Higher likelihood of long-term relief than traditional IBS diet
- Reduces histamine release
- Improves quality of life for IBS patients
- Combines well with stress management strategies
- Probably not beneficial to people without IBS
- Risk of nutritional deficiencies if not balanced
- May damage healthy gut flora
- Difficult to maintain over a long period of time
- Can be expensive
Phase 1: Elimination
The first step to the low FODMAP diet is the most obvious: the elimination phase, also called the restriction phase. During this step, foods high in FODMAPs are completely removed from the diet for two to six weeks [18, 20].
This may be the most difficult step of the low FODMAP process because many foods contain these carbohydrates, and they are not easily avoided .
According to the researchers who pioneered the low FODMAP diet, much of the information found online is unreliable or out of date. They stress the importance of trained dietitians and doctors .
Phase 2: Finding Sensitivities
Once FODMAPs have been drastically reduced or eliminated from the diet, dietitians advise carefully reintroducing one FODMAP at a time. In this way, they can test an individual person’s response to each carb [18, 19].
People may have completely different responses to different carbs. For some, the worst FODMAP is sorbitol; others react the most strongly to fructans, and so on. This is why it’s so important to introduce (or “challenge”) the FODMAPs one by one .
Each FODMAP should be challenged for at least three days to determine what kind of symptoms they produce, if any. For example, to challenge with fructose, a person could take a teaspoon of honey every day for three days. If it results in gastrointestinal symptoms, this person is probably sensitive to fructose .
Phase 3: Personalization
Once a person’s tolerance or intolerance to each FODMAP is established, they can start reintroducing the less reactive foods into their diets in small amounts. The point of phase 3 is to add back as many FODMAPs as each person can tolerate. In this way, people can prevent symptoms while avoiding nutrient deficiencies and potential damage to the gut flora [19, 21].
Every person with IBS is different and may tolerate different quantities of different FODMAPs. For long-term health and adherence to the diet, the personalization phase is vital .
We’ve written a guide to help you choose the right foods (and avoid the wrong ones!) on your journey toward a personalized low FODMAP diet.
Benefits of a Low FODMAP Diet
Keep in mind that these benefits are very likely restricted to people with IBS. If you have painful gas and bloating after eating, you may benefit from a FODMAP diet; if not, you should not expect to receive these benefits [20, 22].
Furthermore, FODMAPs should not be excluded from the diet forever. The second and third phases of the low FODMAP diet are as important as the first .
1) Reduction of Symptoms
IBS is sometimes broken down into subtypes depending on whether diarrhea or constipation is more common or occurs at all. These types are IBS-D (diarrhea), IBS-C (constipation), IBS-M (mixed), and IBS-U (neither). The low FODMAP has successfully reduced symptoms in all of these subtypes .
Note that IBS-M and IBS-U are considerably more rare than the other two types. Statistical analysis is therefore difficult in these groups. The low FODMAP diet’s effectiveness in IBS-M and IBS-U patients has not been effectively compared to the more common types .
2) Long-Term Relief
The three phases of the low FODMAP diet have been linked to long-term improvements in the symptoms of IBS. In one study, 57% of people with IBS reported “satisfactory” symptom relief one year after starting the low FODMAP diet process .
Not all measures of long-term relief improved, however. Compared to those eating their “normal” diets, people eating low FODMAP diets missed the same number of work days and visited the doctor at similar rates because of IBS symptoms .
In other words, more than half of people who eat a low FODMAP diet feel better because of it, but it’s no panacea.
3) Reduced Histamine
Histamine is a powerful inflammatory signal. It is involved in allergic reactions and other types of immune response; some foods contain histamine or can increase histamine release .
Therefore, one way that low FODMAP diets may decrease inflammation is by decreasing histamine.
4) Improved Quality of Life
Besides decreasing inflammation and its associated symptoms, the low FODMAP diet improves other quality of life markers in people with IBS. In one study, people with IBS on a low FODMAP diet experienced :
- Reduced feelings of anxiety, depression, and fatigue
- Decreased dysphoria and improved body image
- Less worry about health concerns
- Increased vitality
- Increased social and sexual function
These results are unsurprising, given that worse IBS symptoms are associated with a worse quality of life .
5) Possibly Better than a Traditional IBS Diet
Some researchers believe that the low FODMAP diet is better than conventional dietary advice for improving the symptoms of irritable bowel syndrome. Others are skeptical, but most agree that the low FODMAP diet is at least as effective as conventional advice [30, 31].
In one study of 82 adults with IBS, more people responded more strongly to a low FODMAP diet than to a traditional IBS diet. Furthermore, fewer people reported either no change or worsening symptoms on the low FODMAP diet compared to the traditional diet .
6) Helps Control SIBO
Small intestinal bacterial overgrowth, or SIBO, is a condition whereby the bacteria in the small intestine grow out of control.
People with IBS often also have SIBO; in fact, SIBO is 3 to 5 times more common in people with IBS than in those without. Bacterial overgrowth may be responsible for some (or even most) IBS symptoms [32, 33].
FODMAPs nourish the gut bacteria; therefore, reducing dietary FODMAPs should reduce bacterial growth and control SIBO. Some rodent studies suggest that carefully manipulating the diet may resolve SIBO entirely; however, the relationship between FODMAPs and SIBO isn’t well understood, and further studies are needed .
Does it Improve IBD?
Inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are similar conditions with similar names, but there are important distinctions between them .
IBD includes Crohn’s disease and ulcerative colitis. They are both autoimmune diseases of the digestive system, but while Crohn’s disease can affect any part of the gut, ulcerative colitis affects only the large intestine .
Some researchers suspect that IBD and IBS are close enough to be subtypes of the same disease. If this is the case, then the low FODMAP diet should improve symptoms in some people with IBD.
Who Should Start a Low FODMAP Diet?
People with irritable bowel syndrome may want to try phase one of the low FODMAP diet. Of these, people whose symptoms respond well to phase one of the low FODMAP diet should progress to phases two and three. People who do not have IBS or those who don’t improve during phase one should not proceed [20, 37].
The telltale symptoms of irritable bowel syndrome include :
- Diarrhea, constipation, or both
- Bloating after eating
- Mucus in the stool
- A worsening of symptoms during menstruation
People with mental illness (such as anxiety and depression), past trauma (such as physical or sexual abuse), bacterial infections, or food sensitivities are more likely to develop IBS .
People who are sensitive to fructose and fructans may be at the highest risk; if you often have symptoms after eating fruits, honey, corn syrup, wheat, or onions, you may be sensitive to these nutrients .
If you suspect that you have IBS, talk to your doctor about possible solutions, including a low FODMAP elimination diet.
The Gut-Brain Axis & the Role of Stress
The brain plays a major role in the development of IBS. In fact, chronic stress, mental illness, and traumatic events during childhood may be the most important predictors of IBS later in life [40, 41, 42].
When we’re stressed, our brains produce corticotropin-releasing hormone, or CRH. One of its roles is to change digestive function during a stressful period. The stomach “holds on” to whatever food is inside and prevents it from moving into the small intestine. Meanwhile, the large intestine’s movement increases, sending its contents out more quickly [43, 44].
Meanwhile, stress hormones also increase the internal organs’ sensitivity to pain in a process called visceral sensitization .
As stress worsens symptoms, symptoms can also worsen stress. People with IBS tend to focus on and catastrophize their disease, working themselves up and avoiding social or public situations for fear of symptoms. And around it goes: this stress, in turn, can increase the severity of the disease .
Thus, chronic stress may underpin many cases of IBS. If you suspect that stress causes or contributes to your symptoms, try to address the psychological symptoms as much as the physical ones.
IBS is often comorbid with other conditions – that is, people rarely have only IBS.
Anxiety and depression are common among people with IBS. This is unsurprising, given the close relationship between IBS and chronic stress, but psychiatric conditions aren’t the only common comorbidities [46, 47, 48, 49].
People with IBS may also have urinary disorders, obesity, diabetes, and allergies or other food intolerances .
Stress Management Synergies
Because of this close relationship between the brain and the gut, therapies that target stress levels can reduce IBS symptoms. These may be combined with a low FODMAP diet as part of a long-term management plan. Stress management strategies that have successfully improved IBS symptoms include:
- Yoga 
- Cognitive behavioral therapy (CBT or “talk therapy”) 
- Interpersonal psychotherapy 
- Stress management/relaxation therapy 
- Hypnotherapy 
- Antidepressants 
Talk to your doctor to find the stress management strategy that’s right for you.
IBD and SIBO
Unlike irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and small intestinal bacterial overgrowth (SIBO) can be positively diagnosed with clinical tools. To diagnose IBD, doctors can use endoscopic cameras, X-rays, and biopsies. To diagnose SIBO, doctors can analyze the bacterial culture of the small intestine [35, 54].
We do not recommend self-diagnosing with these conditions. If you suspect that you have IBD or SIBO, please ask a doctor to investigate your suspicions.
Low FODMAP Diet Side Effects & Risks
The low FODMAP diet has been proven to reduce symptoms in people with IBS, but it is not without risks.
Foods that are rich in FODMAPs also tend to be rich in vitamins and minerals. If people are not careful, they risk health complications from deficiencies in vitamin D, calcium, iron, zinc, and folate .
The first phase of the diet is the most dangerous because of how many types of foods are eliminated, but this period should be brief enough not to cause lasting damage. Consultation with a trained nutritionist will ensure that nutrient deficiencies do not persist through phases 2 and 3 .
Gut Flora Health
A healthy gut flora requires nutritious food in order to survive and thrive. Some types of good bacteria, such as Bifidobacteria, feed on FODMAPs; these populations will decrease on a low FODMAP diet .
When good bacteria ferment small carbohydrate molecules in the gut, they produce short-chain fatty acids (SCFAs) such as butyrate. These, in turn, nourish the cells lining the large intestine. Thus, some FODMAPs may be necessary for optimal intestinal health .
Sticking to a low FODMAP diet can be difficult, especially with a lack of information or in social contexts. Restaurants and other social settings probably won’t have low FODMAP options labeled as such, and people may not know how to identify the right foods on their own .
The best way to increase adherence is through written and in-person consultation with a trained professional. People are much more likely to successfully implement a low FODMAP diet if they have reliable access to an expert who can help them stick to it .
In order to avoid nutritional deficiencies, people on a restrictive FODMAP diet may need to replace staple foods with expensive alternatives like exotic fruits and “pseudo-cereals” (such as amaranth, quinoa, and buckwheat) [55, 57, 58].
Beware of the Marketing Campaigns
Some companies that produce low-FODMAP friendly foods have a financial incentive to promote the low FODMAP diet, even to those who don’t need it. On the other hand, FODMAPs are common in cash crops like wheat and other cereals. Thus, corporations and other organizations with a stake in these crops may lobby against low FODMAP diets .
A meta-analysis of studies on FODMAPs and IBS concluded that, as of 2016, research supporting the diet was free of significant bias. If you’re looking for solid, unbiased information about low FODMAP diets, make sure that your sources are peer-reviewed and published in a scientific journal .
Limitations & Caveats
The low FODMAP diet seems to be better than older IBS diets, but some uncertainty remains.
As some researchers have pointed out, nutritional studies are difficult to design and interpret because they cannot be blinded: the people who participate are always going to be aware of what they’re eating, and their expectations may affect their results .
In fact, given how effective stress management therapies are for treating IBS, a significant portion of IBS cases are probably caused by chronic stress. Working to remove – or at least manage – the underlying stressors may be as important as any diet.
A low FODMAP diet isn’t for everyone. If you choose to try it, it’s important to be honest with yourself and be aware of your biases and expectations. Follow the advice of a doctor or trained nutritionist if at all possible.
Joe (SelfHacked founder) developed the SelfHacked Lectin Avoidance Diet to help himself and clients with chronic inflammation and autoimmunity figure out which foods they are reacting to. He used to have a very severe case of IBS and cured himself completely with this diet, which has similarities to a low FODMAP diet.
The SelfHacked Lectin Avoidance Diet is also an elimination-reintroduction protocol. You remove the food components that pose a high risk for those with food sensitivities until your symptoms subside, then bring them back one at a time to determine what you react to.
Once your inflammation is well-managed, you may even be able to occasionally consume some foods you are sensitive to.
Here are the resources we recommend diving into for more detailed information:
- DNA Vitamin Report and Mineral Report – lets you know which vitamins and minerals you may need more of based on your genetics, especially since low FODMAP diets can be low in certain nutrients.
- The SelfHacked Elimination Diet course, which both breaks down the science and gives you practical step-by-step instructions. The goal is to help you pinpoint your food sensitivities to plant substances and ways to overcome them.
- The All About Inflammation course provides background info and science of inflammation in a layperson-friendly way
- LabTestAnalyzer can objectively tell you if the diet you’re eating is right for you. Check to see if your diet is keeping your labs optimal.
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FODMAPs are fermentable carbohydrates that are normally digested by beneficial gut bacteria. For most people, FODMAPs are harmless; in people with irritable bowel syndrome (IBS), however, they can cause bloating, abdominal pain, and poor stool quality (either constipation or diarrhea).
Some people may control the symptoms of their IBS with a low FODMAP diet: first, foods containing FODMAPs are eliminated from the diet. Next, carbohydrates are reintroduced, one by one, into the diet to test for a reaction. Finally, each person tailors their own diet including FODMAPs they can tolerate and excluding ones they cannot.
The low FODMAP diet reduces symptoms in the short and long term for a majority of people with IBS. It also improves the quality of life, reduces inflammation, and may be superior to traditional IBS dietary advice.