44. Sulfur Intolerace Explained: What Is It? Why Does It Happen? How Does It Increase Histamine?

Are “healthy” foods like broccoli, garlic, eggs, or red meat making you feel worse instead of better?

In this episode of The Histamine Well Podcast, Joanne breaks down one of the most overlooked root causes of food sensitivity, gut symptoms, and chronic fatigue: sulfur metabolism dysfunction.

If you’ve been struggling with histamine intolerance, unexplained food reactions, bloating, brain fog, or fatigue, this episode will help you understand what may really be going on beneath the surface.

🎧 In this episode, you’ll learn:

• What “sulfur intolerance” actually is (and why that term is misleading)
• The difference between sulfide, sulfite, and sulfate
• How disrupted sulfur metabolism impacts your gut, energy, skin, and brain
• The connection between hydrogen sulfide gas and mitochondrial dysfunction
• Why sulfur issues can trigger or worsen histamine intolerance
• Hidden sources of sulfur in foods, supplements, and water
• The role of methylation, molybdenum, and gut bacteria
• Key symptoms of sulfur imbalance (including bloating, fatigue, headaches, and food sensitivities)

Many people are told to simply eliminate more and more foods—but what if the real issue isn’t the food itself?

This episode offers a functional medicine perspective to help you understand the deeper biochemical pathways behind your symptoms and why your body may be reacting the way it is.

Understanding sulfur metabolism can completely shift how you approach healing—and may explain why nothing else has worked.

✨ Want more? Follow on Instagram, Facebook, and YouTube for updates and tips.

📘 New to this journey? Buy The Ultimate Bundle for Managing Histamine Intolerance—your step-by-step guide to manage your histamine intolerance effectively.

 🧪 Curious about your methylation status? Try our at-home Methylation Test! In just 15 minutes, discover if you're over-methylating or under-methylating and receive targeted supplement recommendations to help rebalance. Use code HISTAMINEWELL10 for 10% off.

🎓 Practitioner or student? Join the waitlist for the Histamine & Methylation Online Group Coaching Course starting early 2026!

📆 Work with us 1:1! Book a consultation and take your first step to real healing.

🎤 Have a topic suggestion? Submit it here!

Transcript

0:00

Hi, it's Joanne. If you've been told that healthy foods are making you sick, that broccoli, cabbage, cauliflower, garlic, onion, eggs, or red meat are the problem, or maybe you've noticed you're reacting to supplements like N-acetylcysteine, glutathione, alpha lipoic acid, or MSM, I want you to know that avoidance is really the answer. And if on top of all of that, you are also reacting to high histamine foods like tomatoes, avocados, and citrus. Feeling like your food list is getting shorter and shorter with no real explanation. Then this episode is for you. What's often sitting underneath all of that reactivity, the gut symptoms, the fatigue, the feeling of being toxic, the histamine reactions is something that almost nobody is talking about, it's called Sulfur metabolism disruption. And today we're going to break down exactly what it is, what it happens, and how it connects to histamine in a way that genuinely changes how you understand what's been going on in your body. Welcome to the Histamine Well Podcast. Designed for practitioners and patients alike. This is your trusted source for insights on histamine intolerance, methylation, gut health, women's hormones, and much more. I'm Joanne Kennedy. Your host, naturopath, author, and educator passionate about breaking down complex science into clear, accessible knowledge. Whether you are a health professional or navigating your personal wellness journey, the Histamine Well Podcast bridges the gap between cutting edge research and practical understanding to empower you with the tools to thrive. Hi everyone. Welcome back to the histamine well. Today we're going into territory that I find genuinely fascinating and that I think is massively underappreciated. And that is sulfur. Specifically, what happens when sulfur metabolism goes wrong? Why it matters so much for your gut, your energy, your skin, your brain, and critically how it connects to histamine. Now, I want to reframe something right from the start. When people talk about sulfur intolerance, that phrase doesn't quite capture what's actually happening. It implies that sulfur is the villain. That you need to avoid it. And that framing leads people down a road of restriction that doesn't actually sulfur problem. What we're really talking about is dysregulated sulfur metabolism. And in many cases, something we can call intestinal sulfur overgrowth. That might include what's often referred to as hydrogen sulfide sibo. But here's something really important. It's not always limited to the small intestine. A huge amount of sulfur metabolism and sulfur gas production also happens in the large intestine. So you can be reacting to sulfur quite significantly without ever getting a positive hydrogen sulfide SIBO test. You keep getting told everything looks normal, but you feel anything but normal. If that sounds familiar, stay with me because today I want to give you a framework that might finally make sense of what's been going on. Before we talk about what does go wrong with sulfur, I need you to understand something really fundamental because it changes everything about how we approach this. Sulfur is not the enemy. Sulfur is essential for life. It's the third most abundant element in the body. It plays a role in literally every cell in your body. It's involved in gene expression. How your DNA gets read and acted on protein synthesis. Building the structural components of your body, depends on it. Blood sugar regulation, hormone production, cell structure, and communication, detoxification, your antioxidant defenses. And one of its most important roles, and that's deeply underappreciated is building the intestinal mucosa. That's the mucosal lining in your gut. The layer that feeds your beneficial bacteria acts as a selective barrier and protects the gut wall underneath. Sulfur is a key building block of that structure. It's also essential for creating something called glyco amino glycans, or gags. These are long chains of sugar molecules that form part of your connective tissue, your joints, your skin, and critically your gut lining. So when sulfur metabolism becomes disrupted, the consequences reach far beyond digestion. You are potentially affecting the integrity of your gut barrier, your capacity to detoxify your immune regulation, your skin and your joints. Sulfur is an optional, it's absolutely foundational. And here's something that's really important to understand. Sulfur doesn't exist in just one form in the body. It exists in different states of oxidation, and those different forms behave very differently. The three we care about most are sulfide, sulfite, and sulfate. Sulfide is the most reduced form. It includes hydrogen sulfide gas. Which we'll be spending a lot of time on today in small amounts. It's a normal signaling molecule in excess it's toxic. Sulfite is an intermediate form. It's a stepping stone. Your body produces it during sulfur metabolism and it needs it to keep moving being converted into the next form, and when it gets stuck, problems follow. Then we have sulfate, which is the oxidized, stable end product. That is what we actually want sulfur to become. It's a form that supports detoxification, builds connective tissue and feeds the gut lining. And here's something that's really important for understanding why things go wrong. These forms are interconvertible. Organic sulfur sulfide, sulfite and sulfate can all be converted into hydrogen sulfide gas and vice versa. So this isn't just a simple one-way conveyor belt. It's a dynamic system that can tip in the wrong direction at multiple points. So where do we get sulfur from? We get sulfur from more sources than most people realize, and this matters a lot when we are looking at why someone might be overloaded. The primary dietary sources is amino acids. Methionine, and cysteine. Found mainly in animal protein, eggs, dairy, some nuts, beans, and quinoa. We also get sulfur from brassicas like broccoli, cabbage, cauliflower, kale. Allol compounds found in all vegetables like garlic, onion, leeks, and shallots. Nutrients like biotin and thymine. We also can get it from water. So well water and mineralized water, which can carry significant amounts of sulfur. And then there's the supplements, and this is where people often are really surprised at how much sulfur they're actually consuming. So supplements including N-acetylcysteine, alpha lipoic acid, Sam e glutathione. St. Mary's Thistle, selenium, taurine, MSN, chondroitin and glucosamine. So sometimes when someone feels like they're reacting to everything, they're not reacting to food, they're reacting to their supplement protocol, and that's a really important thing to consider. I'm now gonna run you through how sulfur is metabolized. I'm gonna keep it as clear as I can because understanding this is really important to understanding how things go wrong. You consume methionine from your diet or animal protein mainly. Methionine enters the trans methylation pathway. The methylation cycle, where it eventually becomes homocysteine. Homocysteine is a critical junction point. It has a few options. It can be recycled back into methionine, which keeps the methylation cycle running. This requires folate and vitamin B12. Or it can enter the transsulfuration pathway where it gets converted into cystathione and then into cysteine. This step requires vitamin B6. And directly from homocysteine, small amounts of hydrogen sulfide gas can also be produced. Now from cysteine, the pathway continues in several directions. Cysteine can be converted into hydrogen sulfide gas. It can enter taurine synthesis. It can be used to make glutathione, which is your body's major antioxidant. And when cystine enters the toine pathway, it also has the ability to be converted into sulfate. The key conversion we wanna focus on is this one. Cystine into sulfide, into sulfite, into sulfate. I'll say that again. Cystine into sulfide, into sulfite, into sulfate. That last step sulfite converting to sulfate is carried out by an enzyme called sulfite oxidase. And sulfite oxidase is dependent on a trace mineral called molybdenum. If molebdynum is low, this step can slow down or stall. And this is where a cascade of problems can begin. So let's talk about hydrogen sulfide gas because it's both extremely important in small amounts and highly toxic when it's high. So hydrogen sulfide is a gas transmitter, which is a gas that your body produces on purpose to act as a signaling molecule. In the right amounts, it plays really important roles. It supports nerve function. It helps regulate blood pressure through vasodilation. It protects cells from oxidative damage. It reduces inflammatory responses. So this is not a molecule we want to eliminate. We need it. The problem is when it accumulates beyond what the body can manage. In excess hydrogen sulfide gas becomes toxic. It inhibits the mitochondrial electron transport chain. Essentially jamming the machinery your cells use to produce energy. It also depletes co-enzyme Q 10, which is actually one of the key compounds your body uses to break down hydrogen sulfide gas. So you end up in a vicious cycle. High hydrogen sulfide depletes co-enzyme Q 10 and low co-enzyme Q 10 means less capacity to clear hydrogen sulfide gas. The result is reduced ATP production, reduced cellular energy. And that shows up as profound fatigue, brain fog, poor exercise tolerance, and people just describe they feel really toxic or poisoned or hungover over. Before we go any further, I want to speak directly to the practitioners and students listening. If you're intrigued by histamine and methylation and eager to expand your knowledge in this fascinating area, we offer the Histamine and Methylation online group coaching course. The only program of its kind. It covers everything you need to know about histamine and methylation, providing both the theory and guidance you need to treat these issues effectively in clinical practice. We cover sibo, hormonal imbalances, oxalates, M-T-H-F-R, the four pathways of methylation, including the folate pathway, methionine pathway, tetra hydrobiopterin pathway, and the all important transsulfuration pathway and much more. The program is delivered by detailed online webinars and handouts for you to keep. And for eight weeks you'll meet with me for live coaching calls in a private community space with other practitioners from all over the world dealing with histamine and methylation issues in their patients every day. Together we learn so much. To learn more and apply, visit joannekennedynaturopathy.com So how do we end up with too much hydrogen sulfide? So this is really at the heart of today's episode. So I wanna spend some time here because there are multiple roots to excess hydrogen sulfide. And understanding them changes your approach to the problem. So root one. Methylation issues leading to high homocysteine. If the methylation cycle isn't working efficiently due to things like M-T-H-F-R gene variants, vitamin B12 deficiency or folate insufficiency, homocysteine accumulates. And homocysteine can be directly converted into hydrogen sulfide gas via enzymes called the CBS and the CSE enzymes. So the more homocysteine you have sitting around. The more hydrogen sulfide can be produced from it. The second root is too much cystine. So cystine is also a direct substrate for hydrogen sulfide production. Again, through those same enzymes, the CBS and CSE enzymes. So if cystine is high from excess protein intake or from supplements like N-acetylcysteine, those enzymes can produce hydrogen sulfide in larger amounts. So we have more substrate and then more gas. More hydrogen, sulfide gas. And then we have root three, which can include vitamin B6 deficiency. We need to understand that vitamin B6 is a co-factor for that CBS enzyme. The enzyme that converts homocysteine into cystathione on the way to cysteine. So if vitamin B6 is low, then the conversion is impaired and homocysteine backs up. It builds up and more can get shunted towards hydrogen sulfide production instead of moving efficiently through the transsulfuration pathway. Now root four is molybdenum deficiency and sulfite accumulation. So this is a really important one. When an enzyme called sulfite oxidase can't efficiently convert sulfite into sulfate because molydenum is low. So molybdenum is a co-factor for sulfite oxidase. Well sulfite accumulates. Here's the thing, accumulated sulfite doesn't just sit there harmlessly. It can be converted back into hydrogen sulfide gas rather than progressing forward to sulfate. So we end up with the problem coming from both directions. Too much hydrogen sulfide being produced at the top of the pathway and sulfite converting back into hydrogen sulfide gas rather than clearing through just sulfate. And it goes further than that. Excess sulfites increase reactive oxygen species free radicals, which drive cellular damage and reduce ATP production. So before the hydrogen sulfide problem even fully develops, accumulated sulfide is already creating oxidative stress and depleting your energy. So it's also worth knowing that the sulfur compounds in Brassicas and alliums also feed into this same pathway. So even plant-based sulfur is contributing to that sulfite load. Now, here's where it gets even more interesting. And the gut microbiome is endlessly interesting. And that is the fact that the gut is a major source of hydrogen sulfide, and there are two different bacterial mechanisms worth understanding. So the first involves sulfate reducing bacteria. Particularly the de sulfa fibrio and what's called billophilia. These bacteria produce hydrogen sulfide as a direct byproduct of their metabolism. It's how they generate energy. When they're overgrown, hydrogen sulfide gas production in the gut rises significantly. The second mechanism is different and often overlooked. Certain bacteria including e coli, salmonella, Klebsiella, enterobacters can take dietary sulfur compounds and convert them into sulfate, which is helpful, or hydrogen sulfide gas. Or take sulfite and push it towards hydrogen sulfide gas production. So even without classic sulfate reducing bacteria, you can have significant microbial hydrogen sulfide generation if you have an overgrowth of these bacteria. This is also why someone can test negative for hydrogen sulfide SIBO in the small intestine and still have profound sulfur related symptoms. The large intestine is a massive fermentation environment, and the same gas production can be happening there without it being captured by a standard test. So when it comes to nutrients that really help reduce sulfur, molybdenum is key. So we need to understand that molybdenum is a trace mineral that most people have often never heard of or can't pronounce properly. It took me ages to be able to pronounce it. Now it's easy, but I could never pronounce it. But it's essential for sulfite oxidate.

Joanne Kennedy 17:52

so that's the enzyme that keeps sulfite converting through to sulfate, which we need. Right? So sulfate is stable. It goes into the sulfation liver detoxification pathway amongst other things, and is really helpful for our health. Without adequate molybdenum, that conversion slows, sulfate accumulates and the whole system starts to back up. Another thing worth mentioning here is glyphosate. The herbicide found in many food sources. So it's Roundup. This has been shown to bind to molybdenum, making it unavailable for the body to use. So even if you have someone with adequate molybdenum in their diet, glyphosate exposure can effectively reduce how much is fundamentally available. And this is one of the reasons why some people are more affected than others, despite seemingly similar diets. So how does sulfur link with histamine? When sulfur metabolism becomes dysregulated, when you have sulfite accumulating excess hydrogen sulfide gas, and the oxidative stress and gut irritation that that produces, the net result is inflammation. And inflammation stimulates the cells of your gut to release histamine. They'll also irritate and stimulate mast cells to release histamine. So mast cells aren't the only type of cell to release histamine. We also have smooth muscle cells in the gut amongst other cells that will release histamine. So I see this clinically a lot, is that people will be reacting to histamine foods. And this is often why they find me in clinic. But with more and more questioning, we can understand or sort of pinpoint just from dietary issues or dietary reactions, that it's potentially actually a sulfur problem causing a histamine problem. One of the key questions or signs of that is someone that doesn't tolerate red meat. Now, if they have a histamine issue. Well, the meat needs to be fresh. So many patients with multiple food intolerances on red meat. It's something that they can really, really tolerate and it stabilizes their blood sugar and they feel really good on it. So, you know, as long as they buy it fresh and consume it that day, or freeze it and then thaw it and eat it that quickly that day so that they don't get a histamine buildup. They're normally good on it. So when people are reacting to red meat and getting these sulfur symptoms, that's a classic sign of a sulfur problem that's driving a histamine problem. Eggs are funny. Eggs can be high histamine. People can just be intolerant to eggs. It's one of the foods that come up really high on most food intolerance tests for some reason. And then the brassicas, a lot of them are high fodmap. So the red meat, if people are feeling, toxic from that headaches. Interstitial cystitis is absolutely another symptom of hive sulfur. If they feel really, really tired, then potentially we need to be looking at the sulfur being the main issue at hand. So I've mentioned some of the symptoms of high sulfur. Hydrogen sulfide excess, sulfite excess. But I'll go through a more comprehensive list so it can cause significant bloating. It can cause a lot of strong smelling flatulence, often like sulfur or egg smell, but not always. It can cause diarrhea and constipation or alternating between the two. It can cause abdominal pain and cramping, heartburn, belching. It can cause a lot of neurological symptoms, headaches, eye pain, facial swelling, insomnia, brain fog. Also, in some cases they can feel depersonalization. So that's a sense of being disconnected from yourself and your surroundings. Can also cause joint pain, skin inflammation, flares, interstitial cystitis or bladder pain, and overarching feeling of being really toxic. Overwhelmed, like your body can't cope, and deep, deep fatigue are classic symptoms of high sulfur. So if you recognize yourself in any of this, particularly that combination of digestive symptoms, neurological symptoms, and that underlying sense of being unwell, that doesn't respond to standard approaches, then sulfur is very likely an issue for you, and especially if you've got all the histamine symptoms as well. So working on reducing sulfite in our patients, we obviously need to reduce sulfur in the diet, but not for a long time. Molybdenum is really key. Get Molybdenum to help that conversion of sulfite into sulfate away from hydrogen sulfide gas. We are also looking at healing the gut. We are looking at methylation as well. I should also say all this chronic inflammation is going to really disrupt women's hormones. There's a myriad of things we need to work with when it comes to sulfur issues. So if you believe you've got a sulfur issue, if you're not sure if you want to work with us, we see patients online globally. You can easily book an appointment via my website, which is joanne kennedy naturopathy.com.

23:29

So thank you for joining me. I hope you found this episode beneficial. Be sure to subscribe to the histamine well so you don't miss an episode. Leave a review and you can also share this episode with someone who could benefit. If you have any questions you'd like answered or have a topic you'd like me to discuss, please go to my website, joanne kennedy naturopathy.com, where you can provide us with that information. Until next time, take care and be well.