Protein, one of the three types of macronutrients (the other two being carbohydrates and fat) is made up of twenty building blocks called amino acids. Two of those amino acids contain the atom sulfur in their structures: methionine and cysteine.
A thiol is a compound containing a sulfur atom bonded to a hydrogen atom (also known as a sulfhydryl group in organic chemistry). Of the two core sulfur-containing amino acids, only cysteine contains a thiol group.
Why Sulfur Matters
From a nutritional standpoint, the primary reason we care about sulfur is because three of the liver’s Phase II Detoxification processes (rendering a toxic molecule less harmful) require sulfur: sulfation, glucoronidation, and glutathione-S-transferase. Glutathione (used by that last one) is also most powerful antioxidant in the body, comprised of three amino acids: cysteine (which contains sulfur), glutamine, and glycine.
You need sulfur. You can’t completely avoid it.
Sulfur and Thiol Sensitivity
And yet, some people can’t tolerate sulfur in large quantities. Sulfur sensitivity looks a lot like a histamine reaction, including hives, itchiness, asthma, headaches, nausea, fatigue, flushing, and brain fog.
For people who have a sensitivity to sulfur (or sulfites, which are sulfur atoms complexed with three oxygen atoms), foods and supplements high in the sulfur-containing amino acids can be a problem. Foods high in thiols seem to be especially troublesome (for a list of them, see here.)
What Causes Sulfur Sensitivity
Most of what I’ve found on this goes back to one of two things: a homozygous (two bad copies) genetic mutation in an enzyme called CBS (Cystathionine beta-synthase), and heavy metal toxicity.
The CBS enzyme catalyzes (or drives) the recycling of sulfur containing compounds to get used for other things, releasing ammonia as a byproduct. Cysteine can then get incorporated back into glutathione. CBS mutations are usually up-regulations (meaning they work faster than normal), potentially resulting in an excess of sulfur-containing compounds, and also an excess of ammonia. (Symptoms of too much ammonia include confusion, fatigue, weakness, poor appetite, nausea, and back or abdominal pain.) These people already have too much sulfur floating around; therefore, any food or supplement that adds to the pathway only worsens symptoms.
People with heavy metal toxicity can react strongly to sulfur containing foods because of the very strong affinity between sulfites and heavy metals: effectively, the sulfur-containing compounds can mobilize heavy metals. Anybody who has done IV heavy metal chelation can tell you that pulling a lot of metals out of the tissues at once can make you feel pretty lousy.
Testing for Sulfur Sensitivity
It’s hard to differentiate sulfur sensitivity from allergies or histamine intolerance from the symptoms alone, so diagnosis can be made from an OAT test (urinary organic acid test) indicating one or more of the following: high sulfates, ammonia, orotate, citrate, isocitrate, or Vitamin B6 (pyridoxine).
Traditional labs will also test for urinary sulfates (if the level is greater than 800, I’d suspect this). Other markers that might suggest this include elevated taurine (usually you have to run a full amino acid panel to get this result), or low homocysteine (less than 6).
You can find out if you have the CBS mutation via one of several genetic tests available online. The one I frequently use is called 23 & Me, taking their raw data and plugging it in to geneticgenie.org.
Treating Sulfur Sensitivity
If you’re high in sulfur or sulfites, you’ll have to avoid high sulfur and thiol foods and supplements for a period of time (and again, here’s the list.) This blog also lists recipes for low-sulfur cooking.
The last step in eliminating sulfur from the body is an enzyme called sulfite oxidase, and it uses the mineral molybdenum as a cofactor. This can help.
Dark leafy greens containing chlorophyll like spinach, kale, chard, and collards can help to neutralize excess ammonia. You can also supplement with liquid chlorophyll.
Of course, if you have an underlying heavy metal toxicity, gentle removal should help to improve symptoms of sulfur sensitivity.