SIBO, Small Intestine Bacterial Overgrowth, is an overgrowth of bacteria in the small intestine that typically produces an excess of either hydrogen or methane gas, or both. These are the types of gases that are measured on a breath test. Symptoms usually include bloating primarily, sometimes belching and reflux, and sometimes constipation and/or diarrhea.

But what if your breath test shows no excess of hydrogen or methane, yet you have all the symptoms? It’s possible that SIBO just isn’t the cause—it might be some other form of dysbiosis, or overgrowth of pathogenic bacteria, in the colon. It might be parasites. It might be yeast overgrowth.

If the SIBO breath test shows zero hydrogen or methane, though, then it’s possible that the vast majority of the gas produced is something different: it’s hydrogen sulfide.

Why High Hydrogen Sulfide?

Sulfur is critically important in the body.  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. These amino acids, of course, are also building blocks for protein, so sulfur is necessary for building proteins in general.

Sulfur is also part of the cellular stress response, improving ATP (energy) production so that cells can carry on normal functions even when under stress.

So we need sulfur. But if we don’t have enough of it, one theory is that the body encourages overgrowth of H2S producing bacteria to compensate.

Why We Might Be Low in Sulfur

I wrote here on sulfur intolerance. Causes include heavy metal toxicity as well as potentially glyphosate toxicity–glyphosate is the active ingredient in the herbicide Roundup. Both can cause deficiency in molybdenum, a cofactor for the enzyme sulfite oxidase, which produces sulfate.

Those with a homozygous (two bad copies) genetic mutation in an enzyme called CBS (Cystathionine beta-synthase) may also be at risk, as the CBS enzyme drives the recycling of sulfur-containing compounds. If this isn’t working very efficiently, there may be too much unusable sulfur (leading to sensitivities) and not enough usable sulfur (at the same time leading to deficiencies).

Hydrogen Sulfide SIBO Symptoms

Symptoms of hydrogen sulfide SIBO are similar to those of regular SIBO, except that they also are more commonly linked to diarrhea than constipation.

Also, those who suffer from flatulence with this form of SIBO will likely find that it smells of rotten eggs. (The characteristic rotten egg smell is due to sulfur.)

Hydrogen Sulfide SIBO Treatment

One interesting diagnostic approach, aside from a flat line in regular SIBO testing, is Pepto Bismol. This isn’t a long-term solution, but if you do have hydrogen sulfide-producing SIBO, it will likely help alleviate symptoms. This can help make the diagnosis, but it won’t treat the cause. 

Another diagnostic: while traditional SIBO typically responds well to a low FODMAP diet, those with hydrogen sulfide SIBO will likely respond better to a low sulfur diet. This seems contradictory if the whole issue is low sulfur levels, but again, the problem may be that the body is unable to use the sulfur it receives from food. A low sulfur diet enables the overworked enzymes to play catch-up. 

Epsom salt baths are a good way to circumvent the gut and raise the blood levels of sulfate via skin absorption. The linked study was conducted using 4 cups of Epsom salts in a bath, and soaking for 20 minutes every night for a week.

Since molybdenum is the nutrient cofactor for sulfite oxidase which tends to be low, supplementation is a good idea, especially if levels are found to be low. Dosing is usually around 50-150 mg, but not more than 500 mg per day. 

Even though hydrogen sulfide SIBO doesn’t show up on tests, traditional SIBO treatments typically still work, too. But if the problem is low sulfur, then it’s likely that the overgrowth will recur unless this is addressed.

It’s most important, of course, to find the root cause. Even if you kill the overgrown bacteria and restore normal sulfur levels, if the reason sulfur dropped in the first place is due to toxicity, then identifying and eliminating the toxin(s) is in order.

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