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.

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