Is Onion High in Sulfur?

Sulfur isn’t generally not listed as a nutrient on the nutritional label of foods.

Sulfur also is good and bad depending on where it’s found.

Onions have a very strong taste raw, and make you cry if you inhale the gas through your nose when chopping them, which is known to be caused by the sulfur content in onions but are onions high in sulfur?

Today, I will provide a table showing how the sulfur in onions compares to other commonly consumed foods such as meat, other vegetables, as well as, the other vegetables in the onion family such as garlic and leek.

I will also explain whether the sulfur in onions is bad for you, what kind of sulfur it is, and whether the sulfur can be removed from onions prior to cooking them or during some other process.

Is the Sulfur in Onions Bad for You?

Sulfur comes out of volcanoes and areas nearby are generally evacuated when a large amount of gas is known to have been released or is expected because it’s very toxic in concentrated amounts.

But, it is also found as a solid when it binds with other elements, so is the sulfur in onions bad for you?

I’ll explain below where the sulfur in onions comes from and more about why it isn’t harmful.

But, first here’s a table that shows how the sulfur in onion compares to the levels of sulfur found in other foods:

(source: Journal of Food Chemistry)

From the table, you can see that there is a wide range of sulfur found in different foods.

Some foods have significantly more sulfur than onions, whereas, others have a similar amount or slightly less.

Foods with the most sulfur include:

• Minced beef – 80.8 µmoles/g more sulfur than brown onions
• Eggs – 163.4 µmoles/g more sulfur than brown onions
• Garlic – a whopping 175.3 µmoles/g more sulfur than brown onions
• Leek – 44 µmoles/g more sulfur than brown onions

Leeks and garlic are very similar to onions.

You may be wondering what the relationship is between them.

And if they are in the same botanical family or the same species of plant.

I explained how all of the different kinds of vegetables that are very similar to onion taste which includes garlic, onions, spring onion, shallots, scallions (also called green onions), leeks, and chives in this article about whether leeks are onions.

Brown onions are generally the most common.

These are the types of onions with light brown skin and white flesh.

So, I’ve compared the amount of sulfur for brown onions for the comparison above.

But, red onions, interestingly, nearly double the sulfur that brown onions have.

The measurement µmoles/g is a way of determining the percentage of sulfur per gram of a particular food.

It’s used in science measurement as a measure of the individual atoms in simple terms.

Atoms are very very small parts of something.

Because they are so small, a mole is a very large amount of atoms, which makes it easy to make calculations that a chemist or scientist would usually do. 1 mole = 6.02 times 10²³, this is a very very large number.

A micron (µ), is a very small amount of something 0.000001.

Much like milli is 0.01 of something. Which has the abbreviation ‘m’.

For example, one milliliter is written mL. And one millimeter is written mm.

A quote from the study that extracted the sulfur explains that the sulfur found in foods such as onions has been an interesting field of study:

“Due to the potential importance of sulfate-reducing bacteria (SRB) in the colon, and their association with ulcerative colitis, irritable bowel disease, and Crohn’s disease.”

– Doleman JF, Grisar K, Van Liedekerke L, et al.

The contribution of alliaceous and cruciferous vegetables to dietary sulfur intake. Food Chem. 2017;234:38-45

Where the sulfur in onions comes from?

As you may remember if you’ve taken chemistry, elements on the periodic table can occur as a gas, a solid, or as a liquid.

Some of the sulfur in onions is released as a gas and makes your eyes sting and water.

But, it’s also found as a solid where it’s bound to other elements in the flesh of the onion.

Chemical processes involving rocks are studied in a scientific field known as Geology.

Geology theory states that all rocks come from lava underneath the hard exterior of the earth which is rocks.

Over time rocks will be broken down by the water, and chemical processes to produce soil.

Interestingly, if you go down deep enough into any soil you will find a bedrock of solid rock.

As new rocks are formed by cooling and hardening of the liquid rock beneath sulfur in the lava hardens into a solid.

But, some of it is released as gas.

This rock that contains sulfur is broken down into the soil over time.

And as a plant grows such as onion it takes up some of the sulfur in the roots.

As well as, other chemical elements such as nitrogen.

This is how onions and other fruits and vegetables contain sulfur.

There are a few different chemical combinations of sulfur that naturally occur in nature.

There is sulfur itself which has the symbol S on the periodic table, but there is also sulfate, which is the combination of sulfur and oxygen which has the chemical formula SO₂.

Here’s what type of sulfur is found in onions.

There is a stark difference between the number of sulfur amino acids and the amount of sulfur and sulfate found in different kinds of foods.

Here’s a table that shows the amounts of these different kinds of sulfur in common food:

From the data, a conclusion can be drawn that vegetables have far more sulfur and sulfate than sulfur amino acids.

Whereas, meat and poultry contain far more sulfur amino acids compared to sulfur and sulfate combined.

Red onions have significantly higher amounts of sulfur and sulfate compared to brown onions.

There are also white onions, which are less common but unfortunately weren’t analyzed in the study.

I previously looked at the nutritional differences between red and white onions which gives more detail about which is healthier in this article about red onions vs white onions.

Sulfur is not harmful to consume in the amounts found in virtually all foods.

But, you may be wondering if it’s possible to extract sulfur from foods and whether you can remove it from onions.

Here’s the answer:

To better understand the distribution of the different chemical elements, chemists and scientists have experimented and come up with ways to separate out sulfur found in nature such as in plants, meat, soil, and rocks.

These processes, however, destroy the source material, and therefore, it’s not practical to do it for the onions that you intend to eat.