Written By Krystal Karalli, PNW Intern, Summer 2021

If you are someone interested in nutrition, you know that there are numerous diets out there. While it seems that most are created to achieve a difference in body weight composition, there are some that have been specifically designed to improve digestion and overall health. It is important that we are well informed when it comes to the diets we choose to implement, as some are made to be followed with the guidance of a nutrition or medical professional to achieve successful results that last. 

In this post, we will be diving into a science-backed diet called the Low FODMAP Diet. This odd sounding name is actually an acronym for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols, essentially a group of fermentable carbohydrates. This diet was mentioned briefly in this post, but I think this specific topic needs its own series in order for vegans who are struggling with digestive issues to get a good understanding of how this diet works. In this first part (of 3), you’ll learn the basic overview of the diet including its history, some important definitions, and where certain FODMAPs can be found. Alright, let’s dive in!

Who is a low FODMAP diet for?

Before we unpack what exactly a low FODMAP diet is, let’s first clarify who exactly the diet is for. As stated above, certain diets are specifically designed to improve health and digestion, and this is definitely one of them. A low FODMAP diet is typically recommended by a medical doctor (normally a gastroenterologist) or a registered dietitian nutritionist for those suffering from irritable bowel syndrome (IBS). 

IBS is a functional bowel disorder diagnosed as a result of chronic GI symptoms including lower abdominal pain, diarrhea or constipation (or a combination of both), bloating, and excessive gas. These symptoms may be triggered when eating certain types of carbohydrates in foods. Unfortunately, IBS is a relatively common condition, as it affects between 1 in 7 people globally. Nonetheless, it often goes undiagnosed, meaning, if someone were to try a vegan diet (a diet that is relatively high in carbohydrates) without knowing that they have this underlying cause of GI distress, they may experience a lot of discomfort. 

Although the low FODMAP diet is often followed by people with IBS, it has potential use in those who suffer from symptoms that arise from other digestive disorders such as inflammatory bowel disease (IBD) and SIBO.

A little history 

It's been known for quite some time that certain foods can trigger GI symptoms such as dairy, grains, beans, and cruciferous vegetables. In the last five years, research has shown us the link between certain components found within these foods and the nagging GI symptoms that arise in those who have a hard time digesting them. In 2006, a study was conducted on sixty-two patients with IBS and fructose-malabsorption. The researchers provided a diet that involved restriction of fructan and fructose (two components of foods we will talk more about soon) intake. 

The study was successful in that it helped relieve gut symptoms in a whopping 76% of the patients studied. There were other food restriction studies conducted that offered short term relief for patients but once researchers took a step back and looked at the bigger picture, they saw that many of the food components studied all had similar characteristics and caused the same effects - they were all short-chain carbohydrates that were slowly absorbed or indigestible. Not much later, researchers at Monash University’s department of gastroenterology decided to create a diet that involved broad restriction of these food components. The Monash Group even came up with the term FODMAP. After its creation, the low FODMAP diet underwent lots of testing in order to validate its feasibility and effectiveness. Today, it is used worldwide, with research showing that it reduces symptoms in up to 86% of people with IBS.

How Do FODMAPs cause GI stress?

Before we dive into exactly how FODMAPs cause GI stress, we need to get a little nerdy and break down the molecular structure of carbohydrates first. In a nutshell, carbohydrates are chains of sugar molecules. They can either be just one unit of sugar AKA monosaccharides, two units of sugar, also known as disaccharides, or they can be three to ten units long, in which case they are called oligosaccharides. Interestingly, there are also sugar alcohols, also known as polyols, that are naturally found in nature but can be isolated and used as an additive sweetener such as  sorbitol and mannitol. Monosaccharides, disaccharides, oligosaccharides and polyols are all considered to be short-chain carbohydrates. 

When carbohydrates are consumed, they are usually broken down and absorbed in the small intestine. However, FODMAPS are a group of short-chain carbohydrates (oligosaccharides, disaccharides, monosaccharides, and polyols) that are either poorly digested or completely indigestible by humans. This causes water to be dragged into the small intestine, allowing the carbohydrates to travel to the large intestine. When bacteria in the large intestine get access to FODMAPS, they rapidly ferment them (or break them down) which produces gas as a result. Both the excess gas production and water retention cause the intestines to expand. The highly connected nerves around the intestines then send signals to the brain. For an unknown reason, people with IBS have very sensitive intestines so these signals contribute to the pain they experience. 

Where Are FODMAPS Found?

FODMAPs can be found in a wide range of foods, including fruits, vegetables, grains, nuts, seeds, dairy products, and processed foods and drinks. These foods contain a variety of monosaccharides, disaccharides, oligosaccharides, and polyols. To help you get a better understanding of the different types of FODMAPS, here’s a breakdown with examples of foods that contain them:

Oligosaccharides

There are two different types of oligosaccharides: fructans and galactans. Fructans can be found in a wide variety of different foods. Some examples include grapefruit, dried figs, dates, onion, garlic, leeks, wheat and rye-based grain products, pasta, wheat-based couscous, and gnocchi. Galactans are found mostly in beans, cashews, pistachios, and bitter melon. 

Disaccharides

The most commonly known disaccharide is lactose, the carbohydrate found in cow's milk. Milk, yogurt, soft cheeses, ice cream, and puddings made from cow's milk are all examples of foods that contain lactose. In good news, vegans already do a good job at avoiding these foods though other vegetarians and plant-based eaters may still include these high FODMAP foods.

Monosaccharides: 

The monosaccharide that is specifically considered high FODMAP is fructose. Some examples of higher fructose-containing foods that typically cause GI distress in those with IBS include high fructose corn syrup (HFCS), agave nectar, apples, watermelon, pears, mangos, fresh figs, artichokes, asparagus, sugar snap peas, and fruit juice.

Polyols 

Lastly, as previously mentioned, polyols are sugar alcohols that are naturally found in fruit and some vegetables. Mannitol and sorbitol are usually the sugar alcohols of concern when it comes to the FODMAP diet as they are usually both poorly absorbed by the small intestine. Sorbitol-containing foods include apples, pears, avocado, plums, watermelon, fresh coconut, coconut milk, sugar-free candy, and sugar-free confectionery. Sources of mannitol include mushrooms, cauliflower, celery, sweet potato, and snow peas.

Do all low FODMAP foods cause GI distress for IBS patients?

Although the foods listed above may cause GI upset in those suffering from IBS, note that not all of these foods are triggering for everyone. Every case of IBS is unique to the individual, which means that every person with IBS may experience unique symptoms when consuming different FODMAPs. Some individuals may actually be able to tolerate foods that are recommended to avoid during the low FODMAP diet, and some may find that some low FODMAP foods cause GI distress. Keep in mind that individual tolerance varies, which makes a stronger case for why working with a registered dietitian who has experience working with individuals who have IBS will produce desirable results.

Bottom Line

Now you have a general understanding of what the low FODMAP diet is, who it's for and where certain FODMAPs can be found. Important points to remember are first, the low FODMAP diet is typically prescribed by a registered dietitian or gastroenterologist and involves restricting certain carbohydrate-containing foods for a short period of time (more on this in our second post). Take note that best results are usually seen when the diet is guided by a health professional.

Second, the low FODMAP diet was not designed for weight loss and should not be used for weight loss purposes. Third, although I mentioned some examples of FODMAP-containing foods, keep in mind that not all foods containing FODMAPs were listed above. In the next few posts for this series, we will dive more into the details of the different phases of the FODMAP diet, foods that can be enjoyed while following a vegan low FODMAP diet, and much more so, stay tuned!