Not all onions are created equal

December 3, 2018

Sure there are sweet onions, white onions, red onions, yellow onions, and shallots.  They all taste a little different and shine in different dishes.  That’s because at the chemical level they have unique properties that affect things like the flavor, how they crisp for fried onions, and how much they make you cry.  In addition to the type of onion, there are other factors that affect the properties.  These factors include the nutrients in the soil, the planting method, where geographically the onions were grown, and what time of the year the onions were harvested.

In a recent study, scientists analyzed 20 varieties of onion.  Yes, there really are 20 types of onions!  More than 20 actually.  One of the factors they examined was FODMAP content, and more specifically fructose and fructooligosaccharides (FOS).  FODMAPs tend to cause symptoms for people with irritable bowel syndrome (IBS).  Eliminating or reducing FODMAPs from the diet is increasingly recommended as a treatment for IBS.  Cutting out onions, which are high in FODMAPS, can be challenging as onions are one of the most commonly consumed vegetables worldwide.  Onions are in all types of food from ranch dressing to pizza sauce to chicken stock to guacamole.  They come in all forms: fresh, fried, dehydrated, and as oil.

All onions in this study were high in FODMAPs, as expected.  Interestingly, the varieties that were low in fructose tended to be higher in FOS and vice versa.  Onions grown as “sets” were generally higher in FOS than onions grown from seeds.  The researchers speculate that this is because the set onions were more mature plants.  Varieties high in FOS tend to store better and are more commonly used to make onion powder.  FOS are the main type of carbohydrates in onions, making up to 86% of the total carbohydrates.

In looking at the fructose levels, it is important to also look at the glucose levels.  According to the current understanding of FODMAPs and IBS, foods with fructose in excess of glucose are considered high FODMAP foods.  Interestingly, not all onions in this study had excess fructose, and those that did have fructose in excess of glucose were also high in FOS.  This means that there might be a variety of onion that is on the opposite end of the spectrum, one without excess fructose and also low FOS.  In other words, a low FODMAP onion!  More research of different varieties of onions and growing methods are needed to find that magical low FODMAP onion.

While we wait for that onion to be identified, check out the ETP recipe catalog for flavorful, onion-free dishes.

If you’re interested in the scientific details, check out the following scholarly journal article.

Pohnl T, Schweiggert RM, Carle R. Impact of Cultivation Method and Cultivar Selection on Soluble Carbohydrates and Pungent Principles in Onions (Allium cepa L). J Agric Food Chem. 2018 Nov 21.

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