Do Oats have gluten? Everyone knows that the main rule for a celiac person is to avoid gluten. Then this question should be easy, right?
It may seem absurd, especially if we take into account how advanced the food technology is. We should know if oats have gluten, but the thing is that there is a lack of consensus in this aspect.
First of all, we need to ask ourselves:
What is gluten?
The definition of gluten is quite complex. Generally, it refers to certain groups of proteins which are present in cereals.
More specifically, it gathers two different protein groups: prolamins and glutelins, which are fractions related to the toxic effect in sensitive people.
The prolamins and glutelins can be classified according to their origin. Therefore, they are given the following names depending on the cereal they come from:
*Tribe (“subspecies”) Triticeae.
Rice and corn, are “gluten-free” cereals, which also contain these fractions: zein and zeanin (corn) and orizin and oricenin (rice). However, we know that these two can be taken by celiac patients without any issue.
On the contrary, corn, barley and rye (Triticeae) cannot be eaten by people sensitive to gluten. This is due to the fact that their proteins contain structures that trigger the negative effects.
Phylogenetic tree from Ji et al., (2013). Genetic transformation of major cereal groups.
Oats belong to a different tribe, Aveneae. If we compare the “gluten fraction” (prolamins) from oats with the one from cereals which are not suitable for celiac people we will find some differences:
Prolamins (avenins) make up barely a 5 – 15% of all the protein content from oats, when compared to the 80% of wheat, or 30 – 50% of barley and rye.
However, the most important difference does not seem to lie in the amount, but in the composition. The amount of proline (one of the amino acids that make up these proteins) in non-suitable grains is almost twice as that of oats. This creates structures which are resistant to the digestive enzymes that ensure that certain sequences reach the intestine intact to trigger their toxic effects.
Moreover, there are structural differences when it comes to the amino acid disposition, chain length and molecular weight between the different species. In fact, there is a specific amino acid sequence (Glutamine-Glutamine-Glutamine-Proline-Phenylalanine-Proline) found in wheat, barley and rye, but not in oats, which has been directly related to the toxicity.
* Note: The term “gluten” was coined for wheat proteins in the beginning (gliadins and glutenins). However, since the symptoms were also triggered after eating other cereals, the term was applied to the “active” protein group that triggers the reaction. That is why, according to this definition, oats would be included in the “cereals with gluten” group.
However, this leads to another question. If we have explained that there are differences regarding the structure, molecules and amounts of gluten:
Does the “gluten” from oats trigger the same adverse effects in celiac people as the gluten from wheat, barley and rye?
This question reminds me a little bit of the case of fats. A few years ago, they were all put into the same box, without taking into account their chemical structures, their origin or amount; if a product had fat, it was definitely bad.
Something similar seems to happen with oats and gluten.
First of all, I would like to mention a few cereals corn and rice, like millet or sorghum (all of the suitable for celiac people). All of them contain these “harmful proteins” called prolamines and glutenins, but they do not trigger any reaction. But why is that?
As we can see in the previous phylogenetic tree, the cereals that are suitable for celiac people are far from the Triticeae group. This means that important genetic variants make their proteins “non-reactive” for celiac people. So, even if they are prolamines and glutelins, they are not regarded as “gluten”.
Eating oats in a gluten free diet: scientific evidence
In a study published in 2017 (Aaltonen et al.), they studied the effects of following a gluten free diet with or without oats for a long time. They used a series of surveys, blood tests and histological tests. They conducted the study on a population (n=869) that was diagnosed with celiac disease. An 82% of them ate oats as part of a gluten free diet for the last 10 years.
When they compared both groups (oat consumers vs non-consumers), there were no differences in terms of the symptoms, complications or quality of life. Moreover, the authors observed that taking oats did not affect the recovery of intestinal villi. This is a good factor, since they are usually damaged by the effects of gluten in celiac patients.
These results are not a coincidence: previous studies (Fric et al., 2011; Thies et al., 2014) show how the intake of 100g of oats daily in celiac patients does not alter the intestinal mucosa. Moreover, it does not stimulate the release of antibodies or immune cells.
A meta analysis (Pinto-Sánchez et al., 2017) gathered studies conducted until January 2017. They compared the effects of including, or not, oats to gluten free diets. It reviewed the gastrointestinal symptoms, the antibody levels, improvements in the intestinal tissue and serological markers.
This conclusion, also coincides with the positioning of Canadian experts regarding the intake of oats and the celiac disease (La Vieille et al., 2016).
In spite of the results of said studies and reviews, there are some subjects who do experience symptoms after consuming oats. This shows that there are hypersensitive individuals who do not tolerate oats at all. One reason could be that oats have two amino acid sequences, which trigger the immune system of some patients (hypersensitive) (Glilissen et al., 2016).
When we talk about “non-contaminated” oats we mean that they do not have traces from other cereals (and therefore, gluten).
The problem is that preventing this contamination is quite difficult. Oats may be processed in facilities that also process wheat, rye and/or barley. This contamination can even happen in the crops or during their transport (Thies et al., 2014).
In this way, we should avoid contamination that increases the amount of gluten over 20 ppm (parts per million). That is the international standard to label a product as “gluten free” (Gilissen et al., 2016).
Oats contain a protein fraction that is similar to that of wheat, barley and rye which are not suitable for celiac people. This is the reason why it has been traditionally classified as a “cereal with gluten”. However, there are important structural and composition differences between the gluten from wheat/barley/rye and the one from oats. This means that they will have completely different behaviors.
Many studies have stated that taking “non-contaminated” oats in a gluten free diet does not produce damage or adverse effects in most celiac patients. In generally, its consumption is regarded as safe. However, it is necessary to test the tolerance of the subject. There are cases of hypersensitive patients who experienced similar symptoms with oat proteins (avenins) and the gluten from wheat, barley or rye.
Just like that, most of celiac patients would be able to eat quantities that can reach 100g of oats daily.
Countries like Finland or Canada have officially approved the consumption of non-contaminated oats in a gluten free diet.
Answering the first question: I am celiac, can I consume gluten?
I suggest not taking more than 100g/day, since it is the maximum amount that has been tested in long-term studies.
- Arendt & Dal Bello (2009). The Science of Gluten-Free Foods and Beverages.
- La Vieille et al., (2016). Celiac disease and gluten-free oats: a Canadian position based on a literature review.
- Fric et al., (2011). Celiac disease, gluten-free diet, and oats.
- Gilissen et al., (2016). Why oats are safe and healthy for celiac disease patients.
- Aaltonen et al., (2017). The long-term consumption of oats in celiac disease patients is safe: a large cross-sectional study.
- Thies et al., (2014). Oats and bowel disease: a systematic literature review.
- Ji et al., (2013). Genetic transformation of major cereal crops.
- Pinto-Sánchez et al., (2017). Safety of adding oats to a gluten-free diet for patients with celiac disease: systematic review and meta-analysis of clinical and observational studies.
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