Dear Mark: Milk Thistle and Estrogen, Low Libido, and Pollution Mitigation

Air PollutionFor today’s edition of Dear Mark, we’ve got a three-parter. First, I cover the potentially estrogenic effects of milk thistle extract and discuss whether or not it’s a problem for your endocrine health that outweighs the benefits to liver health. Next, I discuss the reasons why someone might have a low libido eating a paleo style diet, and give a few potential solutions to explore. And finally, Carrie helps a reader figure out some ways to mitigate or avoid the damage wrought by air pollution. It’s everywhere these days, but that doesn’t mean we have to sit there and accept our fate.

Let’s go:

I’ve been drinking a tea with milk thistle while doing a Primally-based sugar detox, as recommended by the authors. A week into drinking like three mugs a day, a friend told me she discovered that milk thistle mimics estrogen, which she can’t have because she’s a breast cancer survivor. I tapered off my drinking of the tea, and yesterday felt some symptoms that makes me think her research is right – but I can’t seem to find anything online that’s conclusive on the issue. Or at least anything I can understand.

Is milk thistle another thing that should go on the “no” list because of the hormone issue? Or is this a myth?


It’s not really a myth, no. Milk thistle has been shown to have estrogenic-mimicking effects, about on par with common soy isoflavones, making them a theoretically poor choice for people with breast cancer. Some sources claim that it’s only the “above ground” parts of milk thistle – the leaves and stalk – that are estrogenic, whereas the seeds are not. I don’t really buy that. The study above used silymarin to mimic estrogen (albeit very modestly), and silymarin is definitely present in the seeds (PDF).

Even so, remember that milk thistle is primarily taken to increase liver health. What’s one of the myriad responsibilities of our humble livers? To process, metabolize, and excrete excess estrogen. We need a healthy liver to get rid of extra estrogen that may contribute to estrogen dominance-related breast cancer. Even if milk thistle is mildly estrogenic, the benefits to our liver health probably outweigh those effects. Sure enough: in one recent study, an herbal conglomerate featuring milk thistle as one of the active participants actually increased estrogen metabolism, effectively reducing the amount of active estrogen by speeding up its clearance from the body. The authors concluded that this likely meant a reduction in breast cancer risk. A very recent in vitro study found that silymarin had a synergistic effect with a common anti-breast cancer drug, while silymarin itself has shown anti-carcinogenic effects on isolated human breast cancer cells.

If you already have breast cancer or have had it and are trying to keep it at bay, milk thistle may be contraindicated; you’d want to discuss that with your doctor, of course. But if you’re looking to improve general liver function, recover from a night of drinking, or save your life after eating toxic mushrooms you found out in a field, milk thistle is a good idea. Plus, I think the totality of the evidence indicates that it’s probably protective against breast cancer, if anything.

You might try a different form than tea, though. Silymarin isn’t very water soluble, making regular old tea an ineffective route of consumption. So any effects you noticed probably weren’t due to the milk thistle. Try a basic milk thistle extract in pill form for a couple weeks to see if those effects return.

I have been on the paleo diet for just shy of a year now and have seen great results. I feel really good health wise and energy wise, but my libido has been really low. I tried to investigate if others noticed this same issue, only to get more confused. For each person claiming low libido, the next blog claims just the opposite. Can you please give me a suggestion as to possible solutions to this issue? My doctor’s suggestion of going off my paleo diet does not appeal to me, I feel great otherwise! And randomly trying supplements from a GNC does not seem like a healthy alternative. Any help would be appreciated. Thanks.


Factors that affect libido?

Calorie intake: Simply put, you can’t go too low. If you’re overweight or obese or have metabolic syndrome, your testosterone production will be inhibited and a lower calorie intake that results in weight loss will generally have a beneficial effect on testosterone levels and thus libido. Calorie restriction also increases testosterone in obese men by improving testicular function and reducing the conversion of testosterone to estrogen.

But that’s in overweight or obese men. In lean healthy young men, extended calorie restriction is associated with lower levels of testosterone. Since you’re seeing “great results,” that makes me think you’ve probably lost the weight you set out to lose. You’re not losing anymore weight, nor are you obese – you’re no longer getting the benefits of consuming all those animal fat calories that were attached to your body. You need to make up the difference, not so much that you start regaining weight, but enough to reduce the negative effects on libido.

Also recall that since this way of eating is so nutrient dense, it’s easy to be satiated on fewer calories – maybe, sometimes, too few calories.

Stress: Stress is a big player in your libido, too, and cortisol has a lot to do with it. As I always say, acute stress is different than chronic stress. Acute (in the first 30 minutes or so) stress actually increases testosterone for a bit. Longer term, cortisol seems to inhibit erections and reduce male sexual arousal, both of which are highly useful barometers of libido. Chronically elevated cortisol also inhibits GnHR, a hormone that stimulates the release of hormones responsible for sperm count, ovulation, sexual activity, and testosterone secretion.

Sleep: Sleep is the foundation for health. And that goes for your sexual health, too. While there are times when acute sleep deprivation can lead to an increase in sexual function, most cases of sleep deprivation lead to lower libido. In men, 33 hours of sleep deprivation lowers testosterone, but not cortisol.

Training: Make sure you exercise. Strength training, especially the kind that involves compound movements, increases testosterone, and a common refrain among lifters (which I can personally corroborate) is that lifting heavy things definitely boosts libido. Sprinting isn’t too shabby at it, either.

Don’t exercise too much, though. Chronic cardio (longterm treadmill running) is particularly bad for reproductive ability, reducing testosterone and semen quality (in addition to other deleterious changes).

Supplementation: Supplementation can help, but, as you say, not randomly chosen supplementation. I also wouldn’t mess with hormonal supplementation without a medical professional’s guidance or advice. Instead, check out the adaptogens, those compounds (usually herbs) that help you respond to stress. They don’t blindly “raise stress” or “lower stress.” Rather, they modify and improve your response to stressors. They help you adapt to the stimulus and mount an appropriate response, whatever appropriate means in a given situation. I discussed several of them in a couple posts last year (here and here). Tongkat ali seems to be particularly good at mitigating the negative impact stress has on libido/testosterone. Maca is another with noted benefits to libido (without affecting testosterone, oddly enough). I also highly recommend Primal Calm, a blend of anti-stress nutrients I use myself.

Specific nutrients: Certain nutrients are particularly important for sexual health.

Zinc – Without zinc, you can’t make testosterone. Slamming zinc won’t really help improve libido unless there’s a deficiency, though. Eat oysters and red meat to keep your zinc topped off.

Cholesterol – Cholesterol is a precursor to testosterone. Your body’s pretty good at making cholesterol, but supplementary cholesterol (in the form of egg yolks or shrimp, ideally, or brains if you want to really get Primal) can’t hurt. Dietary cholesterol can increase strength levels by way of testosterone, particularly if you’re weight training (and you are weight training, right?).

Let’s send it over to Carrie…

What do you suggest for a woman looking to conceive in the next few years to protect herself and future child from inevitable exposure to air and water pollution?

I am a public interest attorney working in the central San Joaquin valley in California for environmental justice for farmworkers. The air quality ratings are frequently “very unhealthy” and my chest gets very constricted whenever I go outside in my work areas. I have only lived in this area for the past year and we will move again in three to five years (mainly to escape the pollution). I live in an area that is in the foothills of the Sierra Nevada mountains, so on nights and weekends I am not exposed to the air and we use a Berkey water filter. My husband and I follow an ancestral eating plan.

I know the easy answer is just to take myself out of the situation, but most of my clients don’t have that luxury. Like most public interest jobs, the salary is punitive, so I am looking for recommendations that are lower cost or proven to be successful.

Thank you for all of the free information you provide. It is truly a public service!



I’ve always worried about the pollution levels having lived in LA/Malibu for so long and I’ve looked into this. Keep in mind that anything that protects you will also protect your baby, or future baby.

Masks may help, not with every possible particulate in the air, but enough to consider:

  • In a 2012 study, R95 activated carbon filter masks were only effective against a single type of airborne polycyclic aromatic hydrocarbon in Hanoi, Vietnam. Most of the worst PAHs still showed up in the urine of participants, indicating that they were making it through the mask.
  • Among people with cardiovascular disease, wearing one of these masks improved cardiovascular health and reduced symptoms of environmental pollution.

Plants! Herbs, shrubs, grass – anything green will reduce air pollution. Consider getting some of the plants from NASA’s list of the top air-filtering plants for your home. This won’t help you when you’re out in the field, but it’ll at least improve things at home.

Glutathione! It’s the major antioxidant and detoxification compound produced by our bodies. How we metabolize and synthesize glutathione helps determine our susceptibility to air pollution, and air pollution’s damaging effects are mostly mediated by increased oxidative stress (which glutathione reduces), so boosting glutathione levels as best we can will also improve our ability to stave off the negative effects of environmental pollution. How do we do it?

Oh, and one last thing. Although there’s evidence that exercising outdoors in high pollution areas increases inflammation and oxidative stress, this is an acute effect that is outweighed by the general benefits of long term exercise. It turns out that exercising outdoors over the long haul makes you more resistant to the negative effects of pollution. So keep exercising, even outdoors! You can reduce your pollution load during exercise, of course, by sticking to the morning (when pollution is lowest) and avoiding major roadways.

That’s about all I can think of. I strongly believe that the most powerful and effective measure we can take is to boost glutathione levels. Pollution is inevitably going to get to us, but we can reduce the impact it has on us by shoring up our defenses. Good luck!

Let’s hear from you guys, now. Got any suggestions for the questions Carrie and I might have missed?

Thanks for reading!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

If you'd like to add an avatar to all of your comments click here!

36 thoughts on “Dear Mark: Milk Thistle and Estrogen, Low Libido, and Pollution Mitigation”

Leave a Reply

Your email address will not be published. Required fields are marked *

  1. Since learning about the strong detoxifying effect of whey protien years ago, my wife and I have incorporated it as a regular part of our diet.

    The only thing I could suggest is that the whey protien specifically be unheated and undenatured, so as to preserve the integrity of the glutathione.

    Best wishes to you, Clare.

    1. @Dr. Mike Tremba: thank you for sharing this 🙂 Some detox-expert told us, that it’s best to take whey protein in the morning, ’cause that should be the time, where the “detoxing organs” need it the most. What do you say?

      1. I have never heard of any research regarding the best time to take it.

        Although my intuition actually would think of the evening as the best time (because that’s when a lot of fat mobilization and detoxifying processes happen), I personally prefer having it in the mornings as well.

        Unless some striking new report comes out, I’d say that any time you take it probably works pretty well for your body. All the best.

    2. I have found the same to be true. I also use to have trouble with a lot of protein powders, but found high quality unheated, undenatured whey to give me no discomfort.

      1. That’s great, Gary. There are so many inferior brands that heat their protien, have toxins in them, and more. Just the same, there are many brands that actually are of high quality, and do the trick. It sounds like you found what works best for you. Thanks for sharing 🙂

  2. I’d add using water from non-municipal sources (that includes bottled water), esp. during pregnancy, to avoid pesticide residue. San Joaquin Valley is known for its concentration of pesticides and nitrates in the ground water.
    We know from a 2007 study by the California Department of Public Health found that women in the first eight weeks of pregnancy who live near farm fields sprayed with the organochlorine pesticides are several times more likely to give birth to children with autism. Plus, there is a positive association between pesticide exposure and development of Parkinson’s disease.

  3. As always, very interesting stuff here! I know that no matter what, if I’m stressed, my libido goes into hiding.
    Also good to know about the glutathione! I’ve never even heard of it!

  4. Low libido could also be caused by excessive use of pornography. It’s something very unprimal and maybe a topic that deserves a post of its own.

  5. I have always found it strange to see people running on concrete in traffic jammed cities filled with pollution. You can actually build up a resistance to that?

  6. Thanks Mark for balanced view of milk thistle. I take it just because I abused my liver as a young man and because I now also take a couple of meds that may affect liver function. Btw eliminating dairy (except for Kerrygold butter) has allowed me to break through recent weight-loss “plateau.” I guess I was too into cheese after all…

  7. NAC’s effects on Iron need to be further studied. While taking NAC at 1200 MG daily, my Serum Iron came back at ALERT HIGH on routine bloodwork, and threw up a red flag for potential hemochromatosis. After ceasing NAC for two weeks, my Iron normalized. A few months later, my iron once again came in at ALERT HIGH. I had been unknowingly taking in 600mg of NAC through a liver detox blend (the NAC was listed in the fine print under proprietary blend, with no dosage listed… I usually read labels critically).

    From further research, I’m concerned NAC potentially Chelates Iron, and also potentially increases absorption of iron in the intestines ( . “The administration of NAC probably increased the absorption of iron through the gastrointestinal tract, causing higher serum iron levels with significant hepatic damage. These results indicate that in a rat model of acute iron intoxication, orally administered NAC may increase mortality.”

    Whether the high serum iron levels were truly anything to be concerned about is up for debate, however I will not touch it after the issues that arose with my bloodwork.

  8. I feel so much better since I have reintroduced raw milk into my diet! I was avoiding milk for a few years because of the supposed “bad” impact on the gut health. The glutathione booster property of raw milk could explain why I have more energy now without changing anything else in my diet (paleo-ish, with potatoes but no grains). Milk is not paleo… but it does me good.

  9. What about low libido for a woman? Anything to help a woman fix this?

      1. I was being serious, and women have other factors involved that men do not deal with. Thank you for your completely unhelpful comment.

  10. Since going on my Primal lifestyle, I had noticed loss of weight, greater energy and increased libido. Since I’m 65 years old, I find the increased libido part somewhat amusing! I’m liking this lifestyle more and more as each day passes.

  11. Wow that’s so interesting that keeping green plants around the home can reduce air pollution, but I guess it makes a lot of sense. I’ve been keeping plants on my office desk for a while now to help with oxygen and to reduce some of the effects of being in air conditioning all day. I find it really helps.

    Great article 🙂

  12. S Acetyl glutathione is a fairly new oral supplement which is supposed to be well absorbed & there is also transdermal glutathione which again may be absorbed better as it bypasses the gut.

  13. Can anyone comment on if you go “to” much veg, you loose libido. Isn’t shaoline moonks surpressing sex drive by going veg only ?

  14. I would be cautious about recommending outdoor exercise for someone living in the Central Valley. We are heading into our third dry season and have reached unprecedented levels of drought in California. Past research on outdoor exercise did not take into effect these environmental changes. This summer could see some of the worst air pollution due to increased forest fires and dusbowl effect from eroding topsoil. It is already happening. Inhaling ash particulates from smoke deep into your lungs is not a good thing!

  15. Brian,

    Libido is highly misunderstood on the interwebs. Do NOT use body buiding sites or other forums for advice on this subject.

    See a naturopath. Why? Because your issue may be either low Testosterone, or low cortisol. Yes, LOW cortisol. It isn’t a “stress” hormone. Just like insulin, you can have too much or too little. If you have chronically low Testosterone, your adrenals have to make up the energy difference and can get tired, but not destroyed. Testosterone blood tests are somewhat helpful, cortisol less so. You can have good weeks and bad weeks, so testing for Adrenals isn’t effective most of the time. You can simply go on low dose Hydrocortisone 15-50 mg a day based on your doctor’s recommendation and assess if you feel better.

    Libido can go away because you work out too much, push yourself too hard, then your adrenals can’t keep up. Most patients who are in this place take cortisol(hydrocortisone is bioidentical) and literally feel libido come back within 24 hours. If it is low T, then that may take months to balance out. You may even need both if your low T created crashed adrenals secondarily. You also need to screen your thyroid with TSH/FH values.

    The easy answer is usually the right one. You Paleo and feel awesome but you are pushing your body at Crossfit or something else or not getting enough calories and you are slowly falling down hill. Carbs will speed up your thyroid hormones and that can increase libido temporarily, but if you don’t have enough T it won’t matter much. Email me if you have more questions, I have personal experience with this as well.

  16. Not sure why Mark doesn’t buy that only above ground milk thistle is estrogenic … unless by ‘not buying it’ he means there’s research for it. Reason I can believe this is due to the fact that roots have many different qualities than the leaves due to the fact that roots produce mostly bacteria/parasite fighting traits due to the fact that they are in the ground, while leaves produce a different kind of setup to try deter animals & insects from eating the leaves. This definitely leaves room for only the leaves of milk thistle to produce the estrogenic traits (both in the leaves, and in our bodies as a result of eating said leaves). Just look at the different traits of dandelion leaves vs roots, it’s quite substantial. I can’t back this up with scientific studies, just my two cents.

  17. Clare, if your chest feels constricted I would recommend a work up for asthma. Inhalers can really help. The constricted feeling is caused by inflammation in the lungs which untreated can cause long term damage. My daughter once said it was like trying to breathe through a straw, which is a pretty accurate description. An allergist or pulmonologist is a good place to start.

  18. Just saw the low libido and I would suggest evaluating the amount of adult related searches you are doing while on the internet. Rule this out number 1 and take a break and check out From personal experience changed my life.

  19. “That’s about all I can think of”–this after a massive amount of extremely helpful information provided free. I carry big loads through city streets most days, always seeking the cleanest lines, deepest alleys, quiet laneways in big, dirty, ugly Toronto. Good to know this stuff and I’ll be checking back on this, as with so much of this helpful information. I can’t believe I avoided Mark for two years because I thought he was some kid showing off his abs, and he turns out to be five years my senior! I’m a near-lifetime vegetarian and keeping my fingers crossed but going paleo this year seems to have kicked the pain in my knees. I’ll give a fuller testimonial at some point.

  20. You know what? Our lifestyles are pretty damn outrageous when we can’t exercise outside anymore without causing ourselves more harm than good. What in the holy F*&! are we doing to our planet? Our home? Our one and only place where we breathe and eat and drink? We’ve got to change how we live, people. If it’s this bad, now, then what will it be like in another 10 years? What about 20 years? Are we all going to walk around with gas masks on?

    Please get involved politically and do what you can to create more change to clean up our world.

  21. I have a high amount of antimony in my blood and cannot find the source. I do not live in an industrial area. Is it possible that my organic plant protein could be contaminated? I am a very clean eater and knowledgeable in fitness and nutrition as I am a personal trainer. Going crazy trying to find the source

  22. Regarding NAC you mention, “Unfortunately, most glutathione supplements don’t work very well because they just get broken down in the gut.”

    There are actually numerous scientific articles that involve human tests that include oral NAC and show notable plasma levels. One, that has to do with ‘End Stage Renal Disease,’ also has healthy control subjects. Those with ESRD were in two groups – one group got 1200mg of sustained release NAC and the other got 600 mg NAC. The healthy control group got 600 mg of sustained release NAC. There is a chart showing plasma levels. Scroll about halfway down the page to see the chart and click on it for a better view; here you can see how 600 mg of sustained release NAC looks in the average persons plasma levels.

    Here is the link:

    I use sustained release NAC 600 mg two to three times a day. With my MCTD it makes so much difference for me. I NEVER wanted to take walks and felt uncomfortable all the time. Now I suddenly get the feeling I want to take a walk. It changed my quality of life.

  23. Thoughtful comments ! I learned a lot from the analysis ! Does anyone know where my assistant might obtain a sample a form copy to fill out ?

  24. My estrogen went from 38.5 to 342. I took milk thistle and wonder if that is what caused it. I gained over 5 lbs now and cannot lose it.
    What can I take to lower estrogen? I am taking calcium glucinate and dim?
    Please if someone can advise me it would be greatly appreciated.

  25. What are your thoughts on liposomal based supplements?

    I have just started the 21day keto program and am looking at taking a Liver/Gallbladder support supplement in a liposomal base of purified sunflower seed lecithin containing Liquid extracts of Dandelion (root), Gentian (root), Solidago virgaurea (aerial parts), and Myrrh (Oleo-gum-resin). However I don’t want to overload my liver and gallbladder with a liposomal supplement since I am now eating a lot more fat…