Doctor's Note

More than 35 years ago, studies started implicating sulfur dioxide preservatives in the exacerbation of asthma. This so-called “sulfite-sensitivity” seems to affect only about 1 in 2,000 people, so I recommended those with asthma avoid it, but otherwise I considered the preservative harmless. I am now not so sure, and advise people to avoid it when possible. How could companies just add things to foods without adequate safety testing? See Who Determines if Food Additives are Safe? For other additives that may be a problem, see Titanium Dioxide & Inflammatory Bowel Disease and Is Carrageenan Safe?

For more on the relationship between hydrogen sulfide and inflammatory bowel disease, see my video Preventing Ulcerative Colitis with Diet. More on this epic fermentation battle in our gut in Stool pH and Colon Cancer.

Does the sulfur-containing amino acid methionine sound familiar? You may remember it from such hits as Starving Cancer with Methionine Restriction and Methionine Restriction as a Life Extension Strategy.

These short-chain fatty acids released by our good bacteria when we eat fiber and resistant starches is what may be behind the second meal effect: Beans and the Second Meal Effect.

What about Crohn’s? Glad you asked! See Preventing Crohn’s Disease With Diet and Dietary Treatment of Crohn’s Disease.

If you haven't yet, you can subscribe to my videos for free by clicking here.

To post comments or questions into our discussion board, first log into Disqus with your account or with one of the accepted social media logins. Click on Login to choose a login method. Click here for help.

  • Nevo

    Recently started drinking store bought almond milk. The label says it contains “vitamin A (synthetic), folic acid (synthetic) and added selenium, magnesium and calcium- as well as B12 and vitamin D-2. All the brands at Whole Foods add these supplements. My question: are these small doses of “A” and folic acid safe to ingest on a day to day vegan diet? And what about the added minerals, are they natural to our body in supplemental form? I could make my own almond milk, but store bought is often convenient and maybe these supplements are a good thing?

    • baggman744

      Everytime I pick up a carton of almond milk and read the ingredients, I put it back. There’s just too much “stuff” in there I don’t need or want. Instead, why not just eat (*almost) raw almonds.
      *(raw almonds are illegal in the US)

      • Karen

        I make almond milk the easy way. Just toss them in a high-powered blender with water, maybe a few dates and some vanilla, and sometimes with cashews.
        Don’t bother with the ridiculous straining through a nut milk bag and the waste of all that almond solids. It settles in the pitcher and in a glass or bowl. But so what. Just shake the pitcher and keep a spoon in the glass while you drink it..

        • baggman744

          Sounds like a great recipe. Thank you. It really is a shame we can no longer buy raw almonds from the US, but like most things in life, we haven’t the choice.

          • fineartmarcella

            I’ve bought them online and sprouted them in the past from a company in Cal that flash steams them, meets the standards, but doesn’t kill the seed, I used to buy them all the time, here’s the bit on how they pasteurize and keep them in a raw state ,

        • fineartmarcella

          I rarely strain things either, don’t want to miss out on any nutrients that I paid for! Besides, I always thought anything left like little chopped up almonds would taste good in breakfast cereal anyway :)

    • Joseph Gonzales R.D.

      Hi Nevo. I think you mention great points about fortified foods. I would suggest foods like plant-milks or other fortified foods (cereals, nutritional yeast) are not as risky as actual daily multivitamins. Many of these fortified foods may offer some advantages for those who lack proper nutrition throughout the day. You could see where you fall short (if at all) from micronutrients and go from there. I agree that high doses of minerals (iron, copper) are probably more risky. In short, if you’re concerned about the fortified stuff than avoid it and make certain you obtain everything from whole foods (still take B12), but I try to be practical and feel fortified plant-milk is of little worry for most. Besides, many folks may have a hard time obtaining enough calcium and B12, therefore a cup of fortified almond milk could help.

      • Nevo

        Thank you, but does the data show that man-made (formulated and derived) calcium is safe for humans? I’ve read studies that say it is not (calcified arteries, and other scary stuff). I assume humans got their calcium from plants, and that this fortification is just an experiment with unknown consequences. You mention fortified plant-milks are of little worry for most, but all the vegan doctors I follow (the ones we all know about here) state to avoid folic acid, and now someone posted the other day that Mcdougall preaching against Vitamin D supplements —– he thinks they are wrong and harmful. So I am wondering what has you convinced these fortified dairy-free plant-milks are “Of little worry to most.”? Thanks. I am wondering if your opinion is based on the scientific evidence Dr. Greger has studied, or is it on something else?

        • Joseph Gonzales R.D.

          Calcium supplements have been shown to be harmful here increase prostate cancer risk. The largest intervention study on a vegan diet that I know of showed better overall nutrient intake, but calcium was one nutrient that was very low Nutrient intake in the GEICO multicenter trial: the effects of a multicomponent worksite intervention. You can certainly avoid. Sure, small amounts of these potentially harmful vitamins (vitamin E, D, and folic acid) are found but I have yet to see a study talking about the dangers of plant-milk. How having fortified plant-milk can lead to an early death. Never seen anything like that. I think making your own plant-milks may be best, and you are right to obtain calcium from whole foods. That is great. Clearly you are very educated on this :) When I say of little worry to most I think of it like carrageenan. No, we don’t want tons of carrageenan in the diet, but if there is some in healthful foods then we may not want to avoid that product completely.

          • Nevo

            Hey, thank you Joseph. I am not surprised that studies have not been done on the plant-based milks, but calling these “plant-based milks” by the industry (as well us all of us here (me included)) is probably misguiding and missing the point to the big picture here : store bought plant-based milks are not plant-based milks, they are “plant-based milks with synthetic vitamin pills mixed in – and also non-food sources of minerals mixed in”. Either take your pill in a little marble sized factory made form, or let the the food manufacturer put it in there (the pill) in the factory. It’s all the same, and from this I think we should be safe to conclude there are serious red-flags out there regarding eating fortified grains, milks, and other stuff. Most of the stuff we read just is published studies that show the good studies.

          • Larry

            I have used Silk Soymilk and other commercial “organic” soymilks daily for years. I recently became concerned about what was happening in my body with all that calcium. Silk recently went from 30% RDA calcium to 45% in an 8 oz. glass. Disgusting! I’m suspicious of possible kidney stones and joint pain due to so much calcium. Walking and weight bearing exercise are the best, proven ways to prevent osteoporosis caused by the body of seniors doing bone calcium dumping

          • Lawrence Woodhams

            The body says “Hey no serious weight bearing demands here in this chair most all day (see Wollf’s law in orthopaedics); why am I lugging such heavy bones; I think I’ll lighten up!” By the way, spread the word, Westsoy Soymilk has no added vitamins or minerals.

      • Timar

        I don’t agree that ordinary, daily multivitamins are “risky” and think that many people advocating whole food diets (like myself) are biased against supplements they consider “unnatural”. As I wrote in a comment to an obviously biased video on mutivitamins, multivitamins have actually been shown to significantly decrease age-related macular degeneration and cancer incidence in a very high quality study of male physicians (PHSII). This study has also shown a non-significant decrease in all-cause mortality. This is in agreement with most epidemiological studies associating multivitamin use with modest beneficial effects. One may conclude from this evidence that the effect is very modest (compared to diet and other lifestyle factors) and hence consider multivitamins “a waste of money” (I don’t think so – a nickel a day for ~10% lower risk of cancer and macular degeneration seems like a very good deal to me) but certainly not that they pose any risk – at least not in the case of iron-free RDA-dose multivitamins similar to the Centrum used in PHSII.

      • It is all relative… if you are replacing dairy with plant milks I would say that health wise a positive step. Learning to read labels and purchasing foods with less additives is generally good. You would expect the amount of persistent organic pollutants to be higher in dairy than in plant milks. The track record for consumption of isolated nutrients in the absence of confirmed deficiency is poor… exception being Vitamin B12. There is one Soy milk product which has only two ingredients on the label… soy beans, water. Calcium is generally not a problem. Folks worried about the strength of their bones would do more in my opinion to focus on getting 150 minutes of weight bearing activity in lieu of thinking that taking calcium pills will fortify their bones… studies don’t on the whole support this. The best source for understanding this issue is Building Bone Vitality by Amy Lanou.

    • Thule

      If you like oatmilk, try out Organic Oatly. Nothing added.

  • Timar

    A correction: I don’t know about the U.S. legislation, but organic wine is regularly sulphurated the EU. This is simply because non-sulphurated wine may turn bad very quickly and there is no real alternative to sulphur as a preserving agent to prevent the formation of highly toxic acetaldehyde – so a tiny amount of sulphur clearly seems the lesser evil here.

    • Justin Bosley

      …or just don’t drink wine. Alcohol causes cancer anyway.

      • Timar

        Yeah, and don’t have sex, too – just think of all those sexually transmitted diseases…

        • Alan

          I gave you a thumbs up and did not mean to. I have given up alcohol and with very good reason. Alcohol is toxic. I will keep having sex with my wife and for very good reasons. Sex is good for our health when done right.

        • Justin Bosley

          I can’t really tell if you are being sarcastic or not so I am just going to assume that you are. I would add would add to your comment “Yeah, and don’t have sex, too – just think of all those sexually transmitted diseases…. that come from premarital sex” So just stay away from premarital sex and you are good. Now it’s a serious comment.

          • Timar

            You are a very serious guy. I’m not. I like wine and women. Seriously ;)

    • Joseph Gonzales R.D.

      Interesting! Thanks for sharing. I think no matter what acetaldehyde is produced from alcohol and the body must detox it, sulfur or not.

      • Timar

        Yes it is, but it can also be produced (sometimes in dangerous quantities) by microbes present in the wine, which is prevented by sulphuration.

        Anyway, I think the overall risk/benefit-relation is very favorable as long as one sticks to one small glas of (preferably) red wine a day with a meal.

      • Timar

        It may be interesting to know that sulphuration of wine is not a modern invention but in fact one of the oldest preservation methods known to men and was rountinely practiced by the ancient Greeks and Romans (besides sulphur they also added resins for that purpuse – hence the famous retsina). That fact that it has stood the test of time for several thousand years suggest that it probably makes some sense.

      • Timar

        A possible explanation for beneficial effects of moderate alcohol consumption may have been uncovered only recently. Apparently, alcohol is not only metabolized to detrimental compounds like acetaldehyde, but also facilitates the endogenous production of – believe it or not – hydroxytrosol (yes, that highly beneficial antioxidant phenol found in olives and olive oil!). It also seems to specifically facilitate the hydroxylation of dietary tyrosol and related phenols – a remarkable synergy which may explain a key health benefit of the Mediterranean diet (wine & olive oil).

        1. Pérez-Mañá et al. Ethanol induces hydroxytyrosol formation in humans. Pharmacol Res. 2015 Mar 20;95-96C:27-33.
        2. Pérez-Mañá et al. Moderate consumption of wine, through both its phenolic compounds and alcohol content, promotes hydroxytyrosol endogenous generation in humans. A randomized controlled trial, Mol Nutr Food Res. 2015 Feb 24.

        • Plantstrongdoc M.D.

          Interesting. There are probably a lot of confounders in the one or two glasses of red wine and health benefits. Some scientists went through hundreds of receipts from a big supermarket and it showed a clear trend – the customers who bought wine also bought the most fruit and vegetables. Not a big significant study, but an interesting observation. And of course the French Paradox – they don’t eat greasy burgers and lard fries size XXL in a fast food joint drinking Pinot Noir. That said I think (hope) that a little wine offers some health benefits :-)

          • Timar

            Charzie, I totally agree. Wine and beer are probably the most ancient of all fermented foods.

            Of course there are a lot of confounders with regard to wine consumption. People who regularly drink wine are more likely to eat a healthy (Mediterranean) diet, are more affluent, better educated and so on. However, health benefits have also been observed after extensive correction for such factors and for moderate consumption of other types of alhocol as well, although less consistent.

            Those studies give a fascinating lead for understanding the observed health benefits of moderate alcohol consumption in general, and wine in particular. I wonder why we haven’t seen any media headlines yet, such as “Alcohol makes your body produce its own extra virgin olive oil” ;)

            Oh, by the way, a little known fact about hydroxytyrosol is that naturally fermented olives actually contain much more of it (about ten times as much by weight, which is a hundred times as much by calories) than even extra virgin olive oil, as the fermentation actually produces hydroxytyrosol from phenolic precursors such as oleuropein.

            “Californa-style” processed olives, however (basically green olives turned black by oxidizing them in tanks with bubbling air and then dying them with iron salts) contain almost none, as the phenols are irreversibly bound to the added iron:

            Charoenprasert S., Mitchell A. Factors Influencing Phenolic Compounds in Table Olives (Oleaeuropaea). J Agric Food Chem. 2012 Jul 25;60(29):7081-95.

            So much for Americans trying to improve on European traditions…

          • fred

            So my real healthful canned black olives stabilized with ferrous gluconate are another load of unhealthy processed crap? I let the BPA leaching can lining go…but now the healthy phenols just aren’t there?

            I think I’ll move to France with all the other coneheads. At least the food might be sort of healthy…

          • Timar

            Sorry to disenchant your industrially processed olives ;)

            You may not need to move to France, though. I’m pretty sure that you can find good quality, traditionally fermented olives in the US. First of all, green olives always retain a fair amount of phenols. When buying black olives, you will certainly find some without added iron gluconate. Even if you can’t always trust the ingredient list, you can trust your eyes. Naturally ripened olives are never uniformly black, they always have some grayish speckels or slight variations in color (that’s why they are treatened with iron gluconate: to give them the uniformely black color customers in the US have come to expect).

            Greek kalamata olives are a good example how natural black olives should look like. Other variesties may have a deeper black color, but never as uniformely as olives dyed with iron.

        • Charzie

          Hey, if eating fermented food is so good for you, why not a little wine, beer or whatever, that is also fermented?

  • Suzanne

    I have asthma and avoid wines due to sulphates, however, never thought about the raisins and dried blueberries I put in my daily oatmeal . . . Learn something every day on this website. Thanks!

    • Julie

      I also avoid sulphates, because they give me migranes. Good news on the raisins–only the golden raisins contain sulphates. Regular raisins are dark because no sulphates were used to preserve the color.

      • CAWS

        Unless your raisins, grapes wine are ORGANIC ; they are heavily sprayed with fluorinated fungicide & pesticide which concentrates when dried. This is why dogs that eat a box of raisins DIE from vomiting,diarrhea, dehydration, kidney failure & painful death as they are more sensitive to acute fluoride poisoning. Same goes for chocolate: fluorine fumigated. F i9s more toxic than lead & only slightly less toxic that arsenic as per it’s position on the periodic table. Water fluoridation is a hazardous waste disposal scheme by the industries that produce it. NEVER FDA approved either.

        • Julie

          Yup, I hear ya. We only buy organic and avoid fluoridated anything. Gotta also watch out for fluoride in antibiotics (fluoroquinolones).

  • Koinhg Yinhg


  • mykamakiri

    Dr Greger,

    How do you feel about vegan probiotic foods, like water kefir? Beneficial?

    • Joseph Gonzales R.D.

      It could be. Dr. Greger mentions the best probiotics in foods. I see no problem taking them if you feel (or doctor is asking) they could be helpful. Typically a high fiber diet produces plenty of prebiotics, which can feed the probiotics already in the gut. During special circumstances they may be more useful. How Should I Take Probiotics? may also be a helpful read. See if these help? Thanks!

  • Plantstrongdoc M.D.

    So when detective Rosewood (Beverly Hills Cop, 1984) said: “Wow. You know, it says here that by the time the average American is fifty, he
    has five pounds of undigested red meat in his bowels” – he was (almost) right all those years ago……. :-)

  • interesting info gan , thanks

  • Guest

    What about sulfur-containing supplements such MSM? Could they cause the formation of sulfur dioxide gas too?

    • Joseph Gonzales R.D.

      That’s a good question. I am not familiar with that supplements and did not find anything on sulfur dioxide gas and MSM.

  • DS

    Given all the health benefits of butyric acid, I’m surprised it’s not available as a supplement.

    • Julie

      It’s in butter! The largest natural source of butyric acid is butter (produced by the bacteria in the cow’s rumen during fermentation of fiber). The fiber is what’s important here. The break down of fiber by our gut microbes provides us with way more benefits than the butyrate alone.

    • cyndishisara

      It is better produced in situ by colonic bacteria fostered or fed prebioticly with a plant based diet PBD. Butyrate is metabolized by our colon cells so promoting their health. It is important to note that we all have a population of bacteria in our bodies which outnumber our own cells by a factor of 10/1. We want health promoting bacteria present. A PBD fosters a healthy microbiome (the name given to this population). We might also need to ingest orally certain bacteria probioticly to foster retinol (active Vitamin A), b-vitamin production (especially b12), digestion of anti-nutrients such as oxalic acid and phytic acid, and immune stimulating effects.

    • CAWS

      Go to Available in several forms & not expensive.

  • More people need to understand that we do not get enough fiber – studies show that we need 30-40 grams of two kinds of fiber a day. I am glad that I found the best source of fiber you can get.

    • Gary O’Reilly

      What fibre source is that Capt?

  • Steveooooo

    I get an itchy throat when i eat dried fruit that contains sulfur dioxide :|

  • Ravi K

    So how can we explain people who are on a whole food plant based diet with little or no processed food who pass noxious hydrogen sulfide gas? A conundrum :-D

  • Larry

    I bought a case of Greek figs last night. They have Sulfites added. I am a vegan. Is this amount of Sulfites okay (I may eat a quarter pound of figs in a day)?

    • Joseph Gonzales R.D.

      Perhaps best to avoid sulfites. Any unnecessary additive is probably best to leave out of the diet. However if you have no allergy to them I see no major concern. Maybe look for sulfur-free dates once this batch is gone? I know dates can be an amazing food based on Dr. Greger’s date video.

      • jm

        I’ve read that soaking in water for an hour (?) will remove a good % of the sulfur from dried fruit. How true is this?

        • Joseph Gonzales R.D.

          Hmmm I am not sure. I looked on pubmed but didn’t see any studies. I wouldn’t think soaking helps, as the entire fruit is coated with sulfur dioxide thus the bright color. Who knows I could be wrong and soaking may reduce sulfur a bit.

          • vegank

            Do you have any suggestions for another type of vegan snack (to avoid sulfides) we could try?
            Or would organic dried fruit be any better? This video (& discussion) was very informative !

          • MattC

            Most dried fruits can be bought without sulfur now. For example, I buy dried apricots from Sprouts Market without sulfur. First, they don’t look good, which I don’t care. Second, it’s a lot more expensive than the sulfured ones.

          • vegank

            Thanks Joseph and MattC, I checked the packaging of the sultanas and cranberries we usually get, they only seem to contain vegetable oil. They were helpful as a substitute when we stopped having any sugary snacks.
            But I will keep looking & probably need to broaden the range of whole food snack we consume.
            It might be worth researching how to make our own rice crackers as well.

          • Joseph Gonzales R.D.

            Yes. There are plenty of dried fruits without sulfur dioxide. Of course fresh fruit is the perfect “fast food” other things like hummus, veggies, whole grain pita, rice cakes, etc are great to have around, but snack preferences vary. I am a huge fan of air-popped popcorn! Good luck

  • b00mer

    Hey, this is off-topic but I wanted to let all my NF friends know – right now the documentary “Cowspiracy” is on sale. The digital download (purchase, not rental) is marked down from $10 to $1 in honor of Earth Day last week. And you can gift it to as many people as you want, for $1 each by entering their email addresses. :)

  • Frannie

    When I met Dr. Greger in Houston in February I asked him about the possibility of heavy metals in Amla powder I get at the Indian market and pesticides on the non-organic goji berries I get at the Asian market. I never thought to ask about sulfer dioxide. After watching this video I ran to the pantry and found this on the goji berries, “Allergen Warning: Contains Sulfites”.
    QUESTIONS: can I wash it off? Will rinsing them also wash off the good stuff? Is the amount of sulfer dioxide negligible? Do the benefits outweigh the risks or visa-versa?

    • Joseph Gonzales R.D.

      Hi Frannie. I am not sure. Someone was thinking the same thing! I responded here if that helps.

  • brec

    COLD pasta? Wouldn’t all pasta be at about the same temperature about a minute or so after passing the lips?

    • b00mer

      Hi brec, I’m guessing that’s in reference to the formation of resistant starch upon cooling.

  • Fidel Castrati

    Even though Dr. G said cruciferous veggies are not associated with bowel disease, it still seems smart to not eat too much high-sulfur plant food, as plenty of sulfide gases can get produced from it. Lower sulfur plant food seems to be the ideal.

  • Cory

    Interesting study on Science Digest today reporting a radical shift in risk factors of colon cancer in two groups: African-Americans in this country and rural South Africans. They swapped diets and found significant improvement (with the African diet) and deterioration with the American diet. One interesting point was that at the start of the study almost half the American subjects had polyps while none of the Africans did.

  • Derrek

    Would about meal frequency? I sometimes eat 4 meals and usually 3-4. Is that ok?

  • Re: “up to 12 g of protein can escape digestion”. Per what? Per meal? Per day?

  • KathyKale

    I thought sulfur was good for skin and the formation of keratin in hair??

  • Lawrence Woodhams

    I commented in a reply to a comment but I don’t know if that is generally noticeable so let me restate: In reference to plant milks being undesirably supplemented with vitamins and calcium: Westsoy makes an organic Soymilk with no added vitamins or minerals. I’m not employed by them (!!! I’m a Physical Therapist Assistant) but I am happy to be able to enjoy Soymilk again after quitting for some time due to concerns relative to this topic.

  • Fidel Castrati

    Hydrogen sulfide gas produced from high sulfur plant foods could be harmful but only those with colonic sulfide-producing bacteria need to be concerned about that, and that is about 50% of people. Those who do have those bacteria could cut back on the high sulfur foods. Eating enough fermentable carbohydrates can help keep numbers of sulfide-producing bacteria down, according to .

  • What about fermented vegetables, are they ok?

  • Anna

    I read that vegan diets are dangerously low in important sulfur-containing amino acids? (See this article: Is that true? How important is sulfur in the diet and are there vegan sources that are high enough to compensate for a lack of meat?

  • Dutch vegan


    I was wondering about black salt (kala namak, it’s indian), since vegan recipes often propose this to mimic the taste of eggs. The reason it resembles an eggy taste, is that it contains sulfur. However, sulfur was not to great for ones health? On the other hand, certain foods that contain sulpur were not found to have a negative impact on health?

    Do you know anything about black salt, has any research been done or do you have recommendations?

    Thank you so much. Love your website, good work!

    Best regards,

    Coen Hendrix (a vegan from holland)

    • Joseph Gonzales R.D.

      Hi Dutch Vegan. Thanks for reposting. I tried searching for black salt using the Indian name (and others) with no avail. I just don’t think it’s been researched enough. It may be like Himalayan salt. ​People often claim sea salt or whatever is healthier, but sodium is sodium and the literature suggests a low sodium intake.

  • MateuszSz

    question for MD ! can poorly functioning pancreas and stomach make it easier for the food to get undigested to colon ? therefore if someone have (like me) have extreme indigestion and very stinky (rotten eggs) gas shoudl get test for pancreas function ? what tests would you reccomend ? greetz from Poland

  • r cian

    What is the percentage of hydrogen sulfide in fecal gas?