Sulfate-Reducing Bacteria and Sulfur Metabolism in GAPS

Gut and Psychology Syndrome identifies sulfate-reducing microbes as one opportunistic group that can overgrow in gut dysbiosis. These microbes metabolize sulfate from food into sulfites, many of which are toxic, and can make sulfur less available for the body to use.^[1]

A Metabolic Group, Not One Species

Campbell-McBride lists several microbial groups capable of sulfate reduction:

• Proteobacteria
• Thiobacilli
• Chromatiaceae
• Desulfotomaculum species
• some gram-positive bacteria
• some fungi
• some Bacteroides^[1]

They are grouped here by a shared metabolic activity rather than by belonging to one bacterial family.

What They Do with Dietary Sulfate

The book says these microbes convert sulfate from food into sulfites and other sulfur compounds. Many of the sulfites are toxic. During overgrowth, more dietary sulfur is redirected through the microbes and becomes less available for normal use by the body.^[1]

This is the mechanism Campbell-McBride connects with sulfate deficiency. The source does not say the bacteria remove sulfate already circulating throughout the body.

The Finding Reported in the Book

Campbell-McBride states that severe sulfate deficiency was found in 95 percent of autistic children and says sulfate-reducing bacteria undoubtedly play an important role in causing that deficiency.^[1]

This is the finding reported in that passage, not a sulfate measurement for every autistic child or for the reader.

Why Sulfate Matters in the GAPS Explanation

Sulfates are required for many functions. Campbell-McBride specifically names detoxification and normal metabolism of brain neurotransmitters.^[1]

A severe shortage therefore fits two recurring GAPS concerns: reduced ability to process toxins and disruption of normal brain chemistry.

Hydrogen Sulfide and the Rotten-Egg Odor

The book names hydrogen sulfide as one toxic sulfur compound produced in this process. Hydrogen sulfide has a characteristic rotten-egg smell. Campbell-McBride says many parents of autistic children report that odor in their child’s stool and gas.^[1]

The odor is a reported clinical clue, not a stand-alone diagnosis of sulfate-reducing bacterial overgrowth or sulfate deficiency.

Why GAPS Returns to Beneficial Flora

After discussing Clostridia, Candida, Bacteroides, sulfate reducers and possible viral activity, Campbell-McBride returns to beneficial flora. She says healthy bacteria keep opportunistic microbes controlled and maintain the gut wall so microbial toxins do not pass through it.^[2]

The treatment target is therefore the microbial ecosystem and gut wall rather than one sulfate-reducing species.

Should You Remove Sulfur-Containing Foods?

The official GAPS FAQ directly addresses this question and says not to remove sulfur-containing foods. Campbell-McBride describes sulfur as important for rebuilding the gut, immunity and liver function, and directs attention to changing the gut-flora balance.^[3]

That distinction matters in a real kitchen. The microbial explanation concerns what happens to sulfur in an unbalanced ecosystem. It is not an instruction to build a separate low-sulfur version of GAPS from this passage.

Our family has followed GAPS since July 2024. As a working, homeschooling mother of six, I want the explanation to lead to something useful at home. Understanding the terms helps me read the books carefully and keep food decisions connected to the protocol. You can read our family’s GAPS story for the experiences behind this blog.

Keeping Useful Notes

If an odor change is what brought you here, record when it appeared, what changed in meals and whether other digestive symptoms changed too. Do not turn the smell alone into a species name or a supplement dose. Take the pattern back to the relevant GAPS food and digestion guidance.

Keep Reading

Read the nutrient and immune-system guide for the wider issue of nourishment and absorption, then return to GAPS immune-system guide.

If you are keeping notes while following GAPS, the 90-Day Family Food Diary in our printable catalog gives you somewhere to record foods, amounts, timing and observations together. Bring the actual pattern back to the relevant GAPS guidance rather than changing several foods at once.

References

1. Campbell-McBride, N. Gut and Psychology Syndrome, 2004 English edition, PDF page 48; sulfate-reducing microbes, reported sulfate deficiency and hydrogen sulfide. Also in the 2015 expanded German edition.
2. Campbell-McBride, N. Gut and Psychology Syndrome, 2004 English edition, PDF pages 48–49, beneficial-flora control and gut-wall integrity.
3. Campbell-McBride, N. Official GAPS FAQs, Diet question 33, sulfur-containing foods and sulfate-reducing microbes.