The Ultimate Guide to the Low FODMAP Diet

FODMAPs are short-chain carbohydrates that are poorly absorbed in the small intestine and rapidly fermented in the large intestine, or colon. Not everyone experiences discomfort when they consume FODMAPs, but FODMAPs are implicated in symptoms of irritable bowel syndrome (IBS) such as diarrhea, bloating, and cramping. 

The low FODMAP diet, which eliminates high FODMAP foods for a limited time and then gradually reintroduces them, provides relief from IBS symptoms for many people. In this article, we’ll talk about what the low FODMAP diet is, what kinds of foods are high and low in FODMAPs, and whether the low FODMAP diet is something you should try. 

What Are FODMAPs?

FODMAP stands for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. The components of FODMAPs are:

Fermentable. Rapid fermentation by bacteria in the gut can result in increased gas production, bloating, and ultimately intestinal pain. 

Oligosaccharides. Carbohydrates formed from a small number of monosaccharides, or simple sugars, such as raffinose and stachyose.

Disaccharides. Carbohydrates formed from two monosaccharides, such as sucrose, lactose, and maltose.

Monosaccharides. The simplest, most basic carbohydrates, such as glucose, fructose, and galactose.

Polyols. Low-calorie sweeteners also known as sugar alcohols, such as sorbitol, xylitol, and mannitol.

(Source, Source)

Why Are FODMAPs a Problem?

The carbohydrates included under the FODMAP umbrella are very diverse, but they have certain problematic characteristics in common:

• They are poorly absorbed. Nutrients in our food are broken down by enzymes in the small intestine and pass into circulation through the intestinal wall. FODMAPs resist this enzymatic action and leave the small intestine intact.
• They have a laxative effect. FODMAP molecules are small, and their buildup in the small intestine causes water to be drawn in to dilute them, which can lead to diarrhea.
• They are rapidly fermented. FODMAPs leaving the small intestine enter the large intestine, or colon, where they are fermented by the bacteria that live there. Rapid FODMAP fermentation produces large amounts of gas as a by-product, which can cause bloating, pain, and a slowing of gut motility.
• They can increase mucosal inflammation and gut permeability. FODMAPs create alterations in the gut microbial community by increasing the number of gram-negative bacteria present. The outer membrane of these bacteria contain lipopolysaccharides (LPS), which are molecules that play a role in inflammation when they are released during breakdown. Consequently, the higher LPS levels can evoke impaired intestinal permeability. This compromised physical barrier may allow toxic substances to cross the intestinal wall.   

(Source, Source)

Who Is the Low FODMAP Diet For?

The low FODMAP diet, specifically designed for those with IBS, is not recommended for everyone. For some it can be helpful, but for others it may restrict necessary nutrients without offering any real benefit.

Low FODMAP Diet Risks

Because this diet involves cutting out a large group of foods (healthy ones, too!), it can risk nutritional inadequacy if not done properly. Potentially reduced nutrients include carbohydrates, iron, fiber, B vitamins, and calcium.

Moreover, most FODMAPs are prebiotics that support the growth of good bacteria and so are beneficial to your gut. Some studies have shown that the low FODMAP diet alters the gut microbiome by reducing populations of beneficial gut bacteria (Actinobacteria, Bifidobacterium, and Faecalibacterium prausnitzii) and promoting dysbiosis.

The low FODMAP diet can also lead to a decrease in fecal butyrate, which is a short chain fatty acid that serves as an important nutrient for many bacteria in the large intestine, as well as supporting the colon’s epithelial lining. Additionally, the diet may reduce populations of bacteria that have immune-regulatory effects, although this hasn’t been shown to have a negative impact on immune function. (Source, Source, Source, Source)

Low FODMAP Diet Benefits

For those who experience symptoms after eating high FODMAP foods, the low FODMAP diet can be beneficial. An array of clinical studies show that up to 86% of people with IBS see symptom relief when following the low FODMAP diet, with success most likely for those who consult with a specialized dietician and adhere closely to the diet. Even so, it is key to note the diet may not work for everyone. (Source, Source)

Predicting Response to the Low FODMAP Diet

Evolving research shows we may be able to predict whether someone is likely to respond to the low FODMAP diet. Predictions may be based on symptom history and by analyzing the gut microbiome composition and function. (Source)

• symptom history: Most people with IBS can identify the foods that make their symptoms worse, and this suggests which FODMAPs they might benefit from avoiding. For example, wheat contains fructans, which are chains of fructose molecules. If you know you have IBS symptoms after consuming wheat, the problem may be the fructans, and you may be able to reduce your symptoms by avoiding foods that contain them. (Source)
• microbiome composition: Symptoms of FODMAP sensitivity are largely due to fermentation by bacteria in the colon, so some studies have focused on identifying which bacteria are involved. Testing stool samples for the presence of known culprits may help determine whether limiting FODMAPs will reduce IBS symptoms. (Source)
• microbiome function: As bacteria metabolize FODMAPs in the colon, gases known as volatile organic compounds (VOCs) are released. The presence of those gases in feces may be an indicator of bacterial activity. A study done at King’s College London found patterns in the baseline levels of fecal VOCs differed between those who responded to the diet and those who didn’t, suggesting another possible method of predicting success with a low FODMAP diet. (Source) 

Symptoms of a FODMAP Intolerance

After consuming high FODMAP foods, you may experience IBS symptoms such as:

• uncomfortable bloating
• abdominal pain
• cramping
• constipation 
• diarrhea
• nausea
• gas (belching, flatulence)

If you experience symptoms like these after eating, you may find it beneficial to start the low FODMAP diet to determine what foods are causing you to feel this way. (Source, Source)

What Is the Low FODMAP Diet? 

The original low FODMAP diet is a protocol designed by researchers at Monash University in Australia. The university recommends the diet only for those who have been diagnosed with IBS by a health care provider, as it has not been found to be helpful for people without the condition.

The Monash protocol calls for an elimination phase in which food choices are highly restricted, followed by a reintroduction phase in which preferred foods are brought back into the diet. The university recommends following the diet under the supervision of a registered dietician or other health care provider. (Source)

FODMAP Sensitivity Varies

When eliminating high FODMAP foods, it’s important to note that an individual may not be sensitive to the entire group of FODMAPs. While some people may react after eating all types of carbohydrates, others may only show symptoms following intake of just one or a few types.

For example, someone may be able to eat apples, which contain monosaccharides, but have symptoms after eating dairy products, which contain disaccharides. Identifying which group of foods are causing symptoms may help pinpoint FODMAP sensitivity. This is complicated, however, by the fact that some foods contain multiple types of FODMAPs. (Source, Source, Source)  

Starting the Low FODMAP Diet 

Keeping track of foods that are allowed and not allowed on the low FODMAP diet, along with monitoring symptoms as they are eliminated and reintroduced, is complex and can be time-consuming.

The initial phases are intended to take place over a number of weeks or months, and these phases should be carefully planned to prevent nutritional deficiencies. 

The low FODMAP diet has three phases. 

Phase 1: Elimination/Restriction 

The first step of the low FODMAP diet is to take high FODMAP foods out of your diet and replace them with low FODMAP foods. This first stage can last anywhere between 2 to 6 weeks. Some people will start feeling better just a few days after eliminating high FODMAP foods, whereas for others it could take a few weeks. 

Remember, for best results it’s important to remain strictly compliant with the diet for the recommended time. This means no cheat days, which can slow down the process. It’s best to work with your health care provider to determine how long you should spend in the elimination stage. (Source) 

Phase 2: Reintroduction

The second step of the low FODMAP diet is gradually reintroducing high FODMAP foods back into your diet. You may not have symptoms from every FODMAP food and you may be able to tolerate small amounts of some, so the point of this stage is to determine which high FODMAP foods you can tolerate and which ones you cannot. 

This phase can be a little tricky, as symptoms may not appear right after eating the food and the time to symptoms can vary between foods. It’s important to leave a few days between foods that are being reintroduced to give your body enough time to react (or not react). A dietician can help you make a detailed timeline. (Source) 

Phase 3: Personalization 

Following the reintroduction stage, you can now begin to develop your lifelong FODMAP diet. You now know which foods are triggers for your symptoms and should be avoided. As well, you know which foods you were able to tolerate in the reintroduction phase, meaning you can incorporate them back in your diet. 

This is why the low FODMAP diet is highly personalized — each person’s food tolerances and intolerances are unique. Even the amount of certain foods that can be tolerated differs from person to person. (Source) 

FODMAP Food List 

Before beginning the low FODMAP diet, you should familiarize yourself with which high FODMAP foods are avoided in the elimination phase, and which low FODMAP foods are encouraged.

The following lists give you an idea of your options, but keep in mind these lists are not exhaustive and don’t include all possible foods. For more detailed lists, you can refer to the food lists from the IBS Diets website. 

And remember: Because the low FODMAP diet requires eliminating a number of otherwise nutritious foods from your diet for several weeks or months, it’s best to consult with a dietician or other health care professional to plan your diet and monitor its effects on your health.

High FODMAP Foods to Eliminate/Reduce

High FODMAP foods include, but are not limited to:

• vegetables and legumes 

• garlic and onions (avoid completely if possible)  
• asparagus 
• cauliflower 
• celery 
• mushrooms 
• peas, sugar snap 
• red kidney beans, soy beans 

• fruit

• apples
• avocado 
• bananas (ripe)
• blackberries 
• cherries 
• peaches  
• watermelon 

• meats 

• chorizo, if garlic is added 
• sausages 

• cereals, grains, breads, and other dry foods

• wheat-containing products (e.g., cookies and muffins) 
• bran cereals
• bread (e.g., multigrain) 
• cashews
• muesli cereal and bars
• pistachios 

• dairy

• buttermilk
• ice cream
• milk 
• yogurt 

• other

• sweeteners (e.g., fructose, honey, jam, sorbitol) 
• beer, wine, cider
• soft drinks
• most fruit juices 

Low FODMAP Foods to Eat 

Foods that are lower in FODMAPs are good to include in your diet, as they can help maintain good nutrition while reducing IBS symptoms.

Low FODMAP foods include, but are not limited to:

• vegetables and legumes

• broccoli 
• carrots 
• cucumber 
• eggplant 
• peppers 
• lettuce and leafy greens
• squash
• turnip 
• tomatoes 

• fruit

• bananas (unripe)
• strawberries
• raspberries
• cranberries
• grapes
• kiwi
• citrus fruits 
• cantaloupe 
• guava

• meats and poultry

• beef
• chicken
• pork
• turkey
• cold cuts, deli meat

• fish and seafood

• canned tuna
• fresh fish (e.g., cod, haddock, salmon)
• seafood (e.g., crab, lobster, shrimp) 

• cereals, grains, breads, and other dry foods

• wheat and gluten free breads 
• almonds 
• buckwheat 
• flax seeds 
• oats
• seeds (e.g., chia, poppy, sesame) 

• dairy and dairy substitutes

• butter
• cheese (e.g., brie, cheddar, feta)
• eggs
• milk (e.g., almond, lactose-free, oat) 

• other 

• coffee and tea
• sugar (e.g., sucrose, glucose) 
• maple syrup
• stevia 

(Source)

What’s the Bottom Line on the Low FODMAP Diet?

The low FODMAP diet is recommended for those whose IBS symptoms may be relieved by limiting FODMAPs. It is a complex, time-intensive process and is not recommended for everyone. The diet involves first eliminating all high FODMAP foods in the diet, then reintroducing them one by one while monitoring symptoms. Once triggering foods have been identified, a well-balanced, nutritious, personalized diet can be developed that helps avoid symptoms of FODMAP intolerance.

Where Can I Find the Best Resources About the Low FODMAP Diet?

Outside of WellTheory’s Ultimate Guide to the Low FODMAP Diet, we recommend looking at:

• What Are FODMAPs: https://www.theibsnetwork.org/diet/fodmaps/ 
• Low FODMAP Diet Information: https://www.ibsdiets.org/fodmap-diet/ 
• About IBS: www.aboutibs.org 

Alongside the links provided above, we also recommend speaking to your health care provider and making an appointment with a dietician to find what approach works best for you.