What to know about the FODMAP diet for IBS

A man picking vegetables in a grocery store

If you have irritable bowel syndrome, or IBS, you might benefit from the low FODMAP diet.

The low FODMAP diet is a short-term therapy that’s used as a tool to help people determine what triggers their digestive problems. It should never be used for weight loss or weight management.

When used as a therapy for IBS, it can be highly successful in helping people gain the knowledge they need to improve gastrointestinal (GI) symptoms.

What are FODMAPs?

FODMAPs stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. To put it more simply, they’re short-chain carbohydrates that aren’t always well tolerated and can cause indigestion for some people.

Some examples of foods that contain FODMAPs are milk, yogurt, apples, pears, watermelon, cherries, peaches, onions, garlic, mushrooms, cauliflower, wheat and rye bread, breakfast cereals, beans, lentils, pistachios, cashews, high fructose corn syrup and honey.

What is the low FODMAP diet?

The low FODMAP diet is an elimination diet, meaning it eliminates foods then slowly reintroduces them to determine which foods cause symptoms of IBS. It has three phases.

Elimination phase: Remove all FODMAPs from the diet. This usually lasts between two and six weeks, depending on how long it takes for symptoms to improve.

Reintroduction phase: Once symptoms are resolved or very mild, choose one item from each of the FODMAP groups to gradually reintroduce over three days and monitor symptoms. This usually takes around 10 to 12 weeks.

Personalization phase: Use the data collected during the reintroduction phase to test your tolerance to different FODMAP combinations in meals at different portions. The goal of this phase is to answer your questions regarding the tolerance of any food you may eat to help you personalize your long-term diet with minimum symptoms.

Using elimination diets to identify food sensitivities

What happens when trigger foods are identified on the low FODMAP diet?

Every person's tolerance will be different. During the reintroduction phase, we reintroduce foods gradually. For example, if we’re reintroducing lactose, we might have the person drink ½ cup of milk on the first day, a full cup the second day, and 1 ½ cups or their regular amount of milk intake on the third day. If symptoms flare up at any point, we know that the amount consumed that day is not tolerable. So, they know they need to stick to less than that amount or they’ll experience symptoms. Keeping a detailed food log during this phase is very important.

Who should avoid a low FODMAP diet?

Because this is an elimination diet, it's very restrictive and time-consuming and requires a lot of attention. Those who have very busy schedules or inconsistent routines may find it difficult to apply the low FODMAP diet. Also, if someone has several other restrictions in their diet, then an elimination diet might not be the best option. It also isn’t a good option for people who are unintentionally losing weight, elderly, or have a history of or are living with an eating disorder.

How does the low FODMAP diet work to help IBS?

Normally, FODMAPs are digested before they reach the colon. But for people who can’t digest a specific FODMAP, it may end up in the colon undigested. The naturally occurring bacteria in the colon ferments those carbohydrates, leading to gas, bloating, altered bowel movements and cramps. By managing the consumption of the undigestible FODMAPs, we reduce the risk of this fermenting and the associated symptoms.

What do I need to think about before starting a low FODMAP diet?

  • Consider learning about other approaches to IBS management, such as following a generally healthy diet, managing your sleep cycle, reducing stress, improving dietary habits around mealtime or increasing physical activity.
  • Consider other issues that could be triggering symptoms, which could result in biased results from the low FODMAP diet. For example, if you’re trying the diet and also experience a great deal of stress, switching medications, modifying your overall diet or making major lifestyle or activity changes, we may not know if any changes are due to the low FODMAP diet or these other factors.
  • Consider timing and budgeting for a successful completion of the diet. So, before you start it, think about whether you have any big events coming up, like a wedding or relocation, or if you’ll be going on vacation in the next few months.

What is a gentle low FODMAP diet?

A gentle low FODMAP diet eliminates a shorter list of items, just foods that are the most common and the highest in FODMAPs. The process is the same, but phases might be shortened.

It may be a better option for people who have a busier lifestyle or are uncomfortable with the more restrictive approach. Discussing this option with a registered dietitian is important to make sure that you are eliminating all of the necessary foods and interpreting the results appropriately.

What if I try the low FODMAP diet and it doesn’t help?

First, we try to determine that the diet is being followed correctly, that we’re looking at all food ingredients and no hidden FODMAPs are being missed.

If the diet is being followed correctly and there has been no improvement, we’ll try to figure out what to do outside of the low FODMAP diet. This diet is just one option for treating IBS. We can also consider other dietary habits, sleep cycles, fiber intake, hydration and physical activity, for example.

In some cases, IBS symptoms may be mimicking other conditions. A deep dive into your symptoms and diet would be important to look for any underlying conditions that may have similar symptoms to IBS.

When should I see a health care professional?

Checking with your doctor to discuss your symptoms before starting the low FODMAP diet is important. Your doctor will perform all necessary testing to rule out possible GI conditions. Once given an IBS diagnosis, meeting with a registered dietitian would be very helpful to find the appropriate nutrition therapy and learn about the low FODMAP diet in detail.

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