Oats, Oatmeal & The Low FODMAP Diet

Ah, oats. They are everywhere! In granola recipes, overnight oat recipes, used as a potential bulk ingredient in savory recipes like meatloaf and of course, used to make that classic warm bowl of old-fashioned oatmeal. Oats are a whole grain that is Monash Green Light approved in certain amounts, but if you look at the app there might seem to be some contradictory information, which we want to walk you through.


First, an oat primer.

Groats & Oats, Steel-Cut to Instant

Sometimes the whole oat grain is called a groat, along with buckwheat groats, wheat, rye and barley groats. In other words, the term groat references the fact that these are whole grains.

When we buy oat groats at the supermarket, they are almost always hulled (after being steamed, to facilitate the hulling process) but are still considered “whole” grains as they have the bran, germ and endosperm intact, which you can see in the image below, courtesy of the Oldways website that we love referring to for interesting and reputable information.

whole grain counsel illustration
Illustration provided by Oldways Whole Grain Council

But let’s focus on the kinds of oats most often called for in recipes. A well-written recipe will specify what kind of oats were used when the recipe was developed and list “old-fashioned rolled oats” or “rolled oats”, which are the same thing and if the recipe just says “oats”, assume that the person means these as well. They are not the same, however, as groats, steel cut oats, quick oats or instant oats. If the recipe requires these, it will most likely specify.

Below we take you through the difference between all of these types of oats. Note that steel-cut and instant oats have not been verified by Monash University. All of these oats described below begin with a steaming process so that the very hard outer hull can be removed before reaching the consumer.

Oat Groats: These get their own entry on the Monash app where it is explained that they are given the Green Light at 1/4 cup or 60 g. Groats, as mentioned before, are the whole grain, steamed and hull removed. Typically they would be eaten as a savory grain, as in a grain bowl or as a side dish.

Steel Cut Oats: These are oats that have not been rolled and are therefore very 3D in form. When we buy steel cut oats at the market they have been steamed, hulls removed, and then have usually been cut into thirds, which makes them small and nugget-like. Their cooked texture is heartier due to their rugged raw texture and cooking time is longer – at least 30 minutes when making them as a hot cereal. They are also sometimes referred to as Scotch Oats, Irish Oats or Pinhead Oats.

Rolled Oats/Old-Fashioned Oats: These begin with the whole grain that has been steamed and hull removed, then they are put through heavy rollers, which compress them into their characteristic flattened shape, sometimes referred to as “flakes” in the industry, as in “oat flakes”. If a recipe calls for “oats”, use these.

Quick Oats: These are the same as traditional rolled oats in that they have been steamed, hull removed and rolled but they have then been chopped into slightly smaller pieces so as to cook more quickly, hence their name. When you measure them right out of the package you will notice that they are a bit “dusty” as some of the oat pieces are very small and this powdery texture will change the results of your cookies, granolas or whatever you are making that has called for traditional rolled oats. As with all recipes, always use the ingredients that are called for.

Instant Oats: These oats have been rolled thinner than the ones described above and chopped into even tinier pieces. They are quite powdery and typically used for a quick hot bowl of oatmeal but do not usually crop us as an ingredient in baking. If you were pulverizing oats in a blender for a smoothie, these would be fine to use but note that they measure out more densely than rolled oats, and the FODMAPs would likely be more concentrated as well.

Oats According to Monash University

If you have looked up oats on the Monash University App you have probably noticed that there are several entries, some of which are specific to a particular country. You might have also noticed that there are entries for oat groats, cooked oats, and “quick” oats as well as raw rolled oats. There are also several entries under “oatmeal”.

oats closeup

Raw Rolled Oats

Half a cup of raw rolled oats, according to Monash, weighs differently in the UK at 60 g, South Africa at 65 g and their generic entry is listed as 52 g. What does this mean? Well, we could extrapolate one of two things. Either processing is different area to area and they actually do weigh differently, or, because the amounts are so close, it might be a matter of volume measurement inaccuracy. Oats can pack down, or be fluffed up, which can result in such variations.

But don’t fret. Look at these as guidelines and really what is important ultimately is how you do with them. How do they feel in your gut when you eat them?

Quick & Cooked

The Monash app lists FODMAP amounts for cooked oats as well as “quick” oats. “Quick” oats are rolled oats that have been mechanically broken down before packaging, as described above. The smaller size of the grain allows for faster cooking but also means that more oats fit into a cup, so they measure heavier. This is important because it means more FODMAPs per measurement and in fact Monash says 1/2 cup of quick oats, which they say equals 47 g, is listed as a Yellow Light and Moderate for Oligos. We are unclear as to how the Oligos amount rises and yet the weight is lighter than that for rolled oats. In our Test Kitchen we have experienced that the weight would be heavier.

Also, the cooked oats app entry is confusing to us. Monash shows South African raw rolled oats as Green Light in 1/2 cup (65 g) amounts. Oats tend to double in size when cooked with water, which you might think would mean that they would then list the approved cooked amount as 1 cup, but they don’t. They list one serving (one serve in their parlance) as 1/4 cup (60 g).

Oats vs. Oatmeal

However, if you look up “oatmeal” on the Monash app, they have several entries, all listed as “uncooked”. They have fine and coarse “organic oatmeal” and also fine and coarse versions of “gluten-free organic” oatmeal.

In the U.S. what we call oatmeal is the cooked version of raw oats. In Monash terms, it is raw oats. Pay attention to these details, so you know what you are actually reading!

Suffice it to say that the app presents some confusing findings that you can see for yourself when you reference it. The two most problematic issues as I see it are that they claim that 1 cup of both fine and coarse organic oatmeal weigh the same and they also state that the fine version is Red Light because of Oligos. We assume the Oligos get flagged due to the higher density of the 1 cup measure, which again is contrary to their listing of them as the same weight as one another. The second major problem is that under “oatmeal” Monash lists one Green Light serving as 1 cup uncooked. This is double what is listed under “oats” and yet we are talking about the same product – raw oats. The only differences are the “organic” and the gluten-free” designations and we cannot fathom how those would affect the FODMAP content to that degree. More testing and explanations are needed.

Oats: Gluten-Free or Not?

Which brings us to a common and great question about whether oats are naturally gluten-free or not. You will find some recipes on FODMAP Everyday® that contain oats and yet are labeled as gluten-free, but you will also see in the ingredient list that we specify gluten-free oats. This is not so much for FODMAPers as it is for celiacs and those with oat sensitivity.

There are two main reasons why oats are included in articles and lists that discuss gluten:

  • Avenin is a protein found in oats that is similar to gluten and has been shown in some studies to activate gluten-reactive T cells in vitro. In actual people, some tests have shown that a small percentage of celiac patients will react to oats.
  • There can also be cross-contamination of oats from wheat or other gluten containing grains during harvesting and processing.

Anecdotally, for people with gluten intolerance, some have negative reactions to oats and others do just fine. Personally I can eat oats in small amounts but I have definitely noticed that if I eat them a few days in a row that I experience heaviness in my abdomen. It doesn’t present as pain, but rather as a general heavy or stuffed feeling that I do not like. It’s like a bloating from the inside, even if it isn’t accompanied by visible bloating on the outside (although that happens sometimes, too). It feels like my GI system is cloggy. Yes, I know that isn’t a scientific term, but part of assessing your reactions to FODMAPs in foods is as much an art as a science. What is true for one person could be very different for you – and it is important for you to learn how to listen to your own body.

How to Buy

I often buy oats in bulk as they are typically less expensive. I can also just buy what I need, which ensures that my stash stays place. When I want gluten-free oats, I buy pre-packaged with that designation such as Bob’s Red Mill. Again, I try to buy small amounts so that my turnover is swift.

How to Store

I store my oats in airtight containers at room temperature in a cool, dark cabinet. While I do freeze some bulk products, oats are not one of them. I find they take on moisture, which might be okay if I am making oatmeal, but not okay when incorporated into a cookie recipe.

So, what to do with all of this information? Oats can be part of a low FODMAP diet, even during the Elimination Phase. Work with your registered dietitian to assess your own tolerances and then take advantage of our oat based recipes.