How to Manage IBS with Low FODMAP Portions


The Low FODMAP Diet is not your typical diet, nor is it really comparable to other things you may have tried in the past. It is best described as a temporary learning experiment that involves elimination, reintroduction and personalization. These three phases help IBS sufferers understand their triggers and take control of symptoms. It is not intended for weight loss or to improve any other specific health condition aside from medically diagnosed IBS.

It’s also not an eat-this-not-that diet. While a list of foods to consume or avoid may work for diets like keto, low carb, or Whole30, low FODMAP revolves around portion sizes. While it is true that one should avoid high FODMAP foods, it is equally important to understand what constitutes a low FODMAP serving, since a low FODMAP food can easily become high FODMAP if consumed in larger portions.

My goal in this article is to shed light on a sometimes confusing and often overlooked aspect of the low FODMAP diet – portion size. I want to give you simple tips and tricks to better understand what a low FODMAP serving is, how to avoid FODMAP bombs, and how to plan meals taking into consideration portion sizes to avoid overflowing your FODMAP bucket.

Portion Size Basics for IBS

As a Registered Dietitian specializing in IBS, I get the following questions a lot:

  • Does portion size really matter? 
  • Do I need to measure foods with FODMAPs?
  • Can I eat several green light or low FODMAP food servings at one time?

The answer to all of these is YES!

How to Interpret Portion Sizes on the Monash App

If you look closer at the Monash app, you’ll see that each food has a traffic light color. This first color related to the FODMAP rating based on a typical serving size. For example, one medium pink lady apple is labeled red, meaning it is high FODMAP at a serving size of 200 grams or 1 medium apple.

If you tap on the pink lady apple, you will find that 28 grams or ⅛ of the apple is moderate in sorbitol. You will also find that 20 grams or ⅛ of a cup is low. This is not a lot of apple, but maybe a nice topping for your morning oatmeal. Many foods have varying traffic light colors based on different portion sizes. This allows us to enjoy small portions of some high FODMAP foods as long as we stick to the green light serving size.

Measuring FODMAPs

As a FODMAP-trained dietitian, I encourage my patients to aim for green light foods in recommended serving sizes, while mostly limiting or avoiding yellows, and generally avoiding reds. Monash is based in Australia, which utilizes the metric system. This means many food portions are provided in grams. By contrast, the English system is also often stated in cups and spoons. While I do think it is important to be aware of your portion sizes, I feel that a measuring cup will suffice. A food scale is not necessary, however not discouraged if you would like to be more precise.

What is FODMAP Stacking?

FODMAP stacking involves eating too many green light or low FODMAP foods at one sitting. While this may result in IBS symptoms for some sensitive individuals, it is something we may only consider if you are having poor response to the diet as a whole.

My advice here is to not overthink FODMAP stacking. Monash established cutoff values to identify foods as either green, yellow, or red, so you can consume several green light foods at one meal and remain low FODMAP. Monash states that it’s reasonable to eat several serves of a green light food at one sitting.

The Challenge with FODMAP Lists

While high and low FODMAP lists are prominent educational tools, they tend to oversimplify. Blueberries for example, are a common source of confusion. Monash defines a low FODMAP serving size of blueberries at ¼ heaping cup or 40 grams. Many lists will green light blueberries based on this reading, but personally, this sounds like a small serving size compared to strawberries, which are low at 10 medium berries or 150 grams. 

Similarly, sweet potatoes are low FODMAP at one half of a cup. Consuming more than this portion pushes the mannitol content into the red zone resulting in a high FODMAP serving size, which may be enough to trigger IBS symptoms in some. While this food is often labeled as low FODMAP per many FODMAP lists, one can easily consume larger portions at one sitting.

Common Food Items That are Easy to Exceed Low FODMAP Portion


Smoothies can easily be what we like to call “FODMAP bombs”. The recommendation is to consume only one low FODMAP fruit serving per meal or snack. It is so easy to exceed one serving of fruit when we are tossing multiple low FODMAP fruits into our blender. Feel free to use ½ of the recommended serving size for two different fruits such as 5 medium strawberries and ½ slightly greenish (unripe) banana into your smoothie to keep your fruit serving in check. 

Instant Oatmeal

Instant oatmeal is low FODMAP at ¼ cup raw, but many of us eat a larger portion of this low FODMAP grain at breakfast time. If you are wanting to enjoy a larger, more satisfying portion, opt for rolled oats. These are safe at ½ cup raw.


Like smoothies, juices are concentrated sources of fruits and vegetables and can easily be high FODMAP. There are a few low FODMAP varieties such as cranberry, lemon, lime, tomato, and fresh squeezed orange juice, however Monash has not tested too wide a range.

It is best to use caution if you want to juice your favorite low FODMAP fruit or vegetable. It may be best to create a blend using a vegetable with no FODMAPs detected such as carrot or limit your low FODMAP fruit and vegetable to the serving of the whole, intact fruit or vegetable. For example, ½ cup of fresh squeezed grapefruit juice contains more than the low FODMAP serving size of ½ cup fresh grapefruit. 

Nuts and Seeds

Like juices, nuts and seeds are easy to overdo, especially if you are just snacking on nuts when hunger hits. Not sure about you but the low FODMAP serving of ten almonds is fairly easy to stick to.

Foods Without FODMAPs

If you look closely at the Monash App, you will see that some foods have the statement “FODMAPs were not detected in this food”. This means that one can eat multiple servings of this food at one sitting without having to worry about portion sizes.

Examples of No FODMAPS Foods Include:

  • Arugula
  • Carrot
  • Clementines
  • Cucumber
  • Grapes
  • Guava
  • Japanese Pumpkin
  • Papaya
  • Parsnips
  • Patty Pan Squash
  • Red bell pepper
  • Rhubarb
  • Rice
  • Strawberries
  • White Potatoes

Quick reminder, FODMAPs are carbohydrates, fibers and sugars. Therefore, pure protein sources such as eggs, poultry, pork, fish, seafood, beef and pure fats like oils and butter (only contains trace amounts of lactose which is not of concern) are low FODMAP.

However, watch out for seasonings and sauces as they often contain garlic and onion and the sneaky fibers inulin and chicory root, which pop up in lactose-free yogurts, protein powders, herbal teas, protein powders, granola bars, and more.

How to Interpret Food Labels for Serving Size

The serving size defined by the food label does not always correlate to the recommended or typical portion sizes provided on the Monash App. It is best to use the Monash app to help you determine how much you can safely enjoy at one meal. 

The ingredients on a food label are listed in descending order, which means the first ingredient is present in the highest amounts and the last ingredient the least. High FODMAP ingredients such as garlic and onion, even when present in portions less than 2%, should be avoided unless the food product is defined as low FODMAP.

Final Takeaways

  • Use the Monash App with FODMAP containing foods.Tap the specific food to discover the appropriate portion size so you can serve yourself the correct portion.
  • Measure FODMAP containing foods. A simple measuring cup can bring awareness to your portion sizes. While it is easier to eyeball a serving size, it may be a good idea to measure FODMAP containing foods especially when you are first getting started. 
  • As a rule of thumb, I often recommend limiting vegetables with a low FODMAP serving size to one to two per meal, unless “No FODMAPs detected” is displayed.
  • Limit fruits to one serving at each meal or snack.
  • If you are ravenous at meal time, include more no FODMAP foods into your meal so you do not have to be as concerned with portion control. Try adding rice, white potatoes, lean proteins, and healthy oils to help you stay full. 
  • Those who have poor response to the low FODMAP diet may want to take a closer look at FODMAP stacking or better yet, follow up with your FODMAP trained dietitian for more individualized recommendations.

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