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Dear Mark: Cruciferous Vegetables and Hypothyroidism, Sprint Frequency, Protein Sources for Orthodox Lent, and Saunas

For today’s edition of Dear Mark [1], I discuss the connection – if one even exists – between cruciferous vegetables (and their goitrogens) and thyroid function. A theoretical interaction exists, but should this impact your decision to eat steamed broccoli? Next, I explain why I recommend one, maybe two days of sprinting a week, in contrast to the exercise studies that often use 3 or 4 days/week sprinting programs to great success. Then, I give a few tips for a person wondering about getting sufficient sources of Primal protein while on an Orthodox Lent fast. And finally, I explore the potential health effects of saunas.

Let’s go:

I read a report on kale and other cruciferous vegetables causing hypothyroidism if eaten too often.

I believe in moderation but this is the first time I’ve heard this. Can you touch on this subject?

Here’s the article [2].

Thanks, Mark.


I almost hesitate to discuss this, because I don’t want people worrying about their broccoli intake or experiencing anxiety whenever kale is served. Yes, cruciferous vegetables [3], which include kale, broccoli, cauliflower, cabbage, kohlrabi, mustard greens, Brussels sprouts, and bok choy, among others, do contain compounds known as goitrogens. Goitrogens reduce the amount of iodine absorbed by our thyroid glands, and at really high levels can actually prevent iodine from being incorporated into thyroid hormone altogether. Animal studies have shown that large doses of cruciferous vegetables like cabbage can interfere with thyroid function.

Here’s the thing, though. Cruciferous vegetables are only a problem when they’re:

So, a raw vegan juicing several kilos of raw Brussels sprouts, bok choy, and kale on a daily basis might have thyroid problems (in addition to fascinating bowel habits), while a Primal eater having a side of steamed broccoli, cauliflower, or cabbage with a steak a few times a week will be just fine. Even a raw kale [7] salad now and then is fine (but probably not a pound’s worth every day). One study [8] looked at the effects of raw broccoli sprouts, which are extremely rich in the goitrogenic compounds people are worrying about, on thyroid health in humans and reported no abnormal findings. Don’t worry too much about cruciferous vegetables. They’re good for you [3] and only harmful in ridiculous situations where most reasonable people will never find themselves.

One quick note: Pregnant women early on in the pregnancy – when thyroid function is most important and thyroid hormone requirements are especially high – may be more sensitive to goitrogens. This usually coincides with taste aversions, so eating too many goitrogenic vegetables is usually hard to do. But it’s worth keeping in mind.

Hi there 🙂

Okay. I’m curious. Most of the studies I’ve read (some of which Mark quoted in his most recent article) put HIIT and Tabata training at approx. 3 – 4 sessions/times a week. Mark advocates to sprint “once in a while”, or once a week in his PB Fitness Book (as per the fitness logbook). So… is sprinting 3-4 times a week too much? would it be less effective and closer to a “chronic cardio” type deal? All the gains from the studies I’ve read are from individuals participating 3-4 times a week for about 12 to 16 weeks.

Thanks! 🙂


Great question. The thing about those studies is that in order to exclude any confounding variables, they generally forbid participants from engaging in other exercises. So in a HIIT study, you’ll just do HIIT and nothing else on the side. You won’t lift weights, or go on hikes, or walk 10,000 steps a day. You’ll be focusing on HIIT and HIIT alone so as to isolate the effects of the experimental condition. The absence of other training coupled with the total dedication to the program allows adequate recovery.

If you weren’t doing anything else (like the study participants), I’d say you could get away with three or four sprinting [9] or HIIT days a week. I think, though, that optimal fitness is achieved through a more well-rounded approach that includes lifting heavy things [10], play [11], lots of slow moving [12], and sprinting [13] (or HIIT [14]). All those activities require recovery time. We can and do learn from fitness studies, but in reality we can’t just take what studies do wholesale. We would fail, or be required to sleep [15] twelve hours a day, or eat 5000 calories.

Another factor to consider: many of these studies use students because they tend to have more free time than working adults. More free time also means more recovery time and (usually) less psychological stress that impacts workout recovery. They’re arguably a better way to study the effects of a training program in otherwise “pristine” people without lots of confounding lifestyle factors.

With regards to sprinting in particular, I usually dedicate an entire day to it. If I do workout in addition, I treat sprinting like a really grueling lower body workout day. I’ll sometimes lift the same day as sprinting, but I’ll mostly stick to upper body lifts like pullups [16], dips, or pushups [17].

I had a question I have not seen answered. I am an Anglican who has adopted some Orthodox practices. In the old church tradition there are fasting and abstinence seasons and days. Lent is the longest and the tradition is to abstain from meat, oils, and dairy for 40 days plus weekends while reducing meals. Food is to be simply cooked or eaten raw if possible.

This does not easily fit with the Primal Blueprint. Any suggestions about what to do during those times? I plan on using tempeh as a protein source but lentils are also an option. It will be hard to keep carbs down without eating a lot tempeh and Natto during the time. Is seitan a solution?


Tempeh is a “pretty good” vegetarian source of protein. Yeah, it’s soy, but fermented soy, and the fermentation process reduces phytic acid [18] and deactivates the lectins [19].

Natto is also advised. Those who can get past the interesting texture, difficult odor, and curious taste to reach the numerous health benefits [20] (including a whopping dose of vitamin K2 [21]) are often pleased they made the effort.

And as far as legumes [22] go, lentils are probably the best and least offensive option. They’re pretty digestible after about 8 hours of soaking and they’re decently nutritious.

As far as I know, shellfish are still allowed during Orthodox Lent, right. If that’s the case, go for those guys. Mussels, clams, shrimp, scallops, lobster, crab, and oysters can easily take care of any animal protein needs. It might be a bit more expensive than you’re used to, but you can’t go wrong with shellfish [23], some of the most nutrient-dense foods around.

I would skip seitan. It’s basically a block of pure gluten [24]. I suppose it’d be okay if you’re totally free of gluten intolerance or sensitivity [25], but it’s more common than many people assume and I wouldn’t want to tempt fate and find out the hard way.

Are eggs [26] allowed? If so, eat some of those.

What else can John eat, readers? Maybe some alternative protein powders? If you can’t do whey, look into some “complete” (meaning a full amino acid profile has been attained by blending different plant protein sources) vegan protein powders for the time being.

Hi Mark, keep it up. You are doing God’s work, and have been a blessing in my life.

Wondering what your thoughts were on the idea of “cleansing” and also steam/sauna. Is there a primal way of looking at these? Health benefits?


Rev. Josh

I’m always curious about those near-universal human traditions with extensive histories. People generally don’t just do stuff for the heck of it. You dig deep enough and you can usually find a kernel of truth there, some health benefit at least partially confirming the tradition’s efficacy.

The sauna is definitely a near-universal human tradition. In the Americas, there are the sweat lodges of North America and the temazcals of Central America. Scandinavia is known for its saunas, particularly Finland. Russia has the banya, Turkey the hamam, and ancient Rome the laconium. People from all over the world have been enjoying the heat for thousands of years, but are there actual, documented benefits to sweating it out in a sauna?

Muscle recovery: Steam saunas appear to improve muscle recovery [27] following exercise to exhaustive failure.

Stress reduction: Most people intuitively know that saunas are relaxing, but they legitimately reduce cortisol [28] over the long term. The sauna experience itself acts as an acute stressor, however, spiking cortisol and heart rate and adrenal hormones [29] – but only for a short time.

Toxin clearance: Contrary to what cynics might give as a knee-jerk response to any question involving the word “toxins,” it appears that there might be something to the idea of “sweating out the toxins in a sauna”:

Any downsides?

Male fertility: Saunas are hot, and heat can negatively impact male fertility [35]. One trial [36] found that sauna usage impaired spermatogenesis in men with normal fertility. This effect was transient and reversible, however.

Heart trouble: People who’ve recently had heart attacks, or who have unstable angina pectoris or severe aortic stenosis may want to avoid saunas [37].

Exposure to carbon monoxide: Wood-fired steam baths, like some temezcals in Latin America, can produce massive amounts of carbon monoxide [38], a known toxin.

For the most part, saunas are safe, and they may be extremely good for you. Even if you “just” enjoy them after a hard workout [39] or as a way to relax, I’d say there’s definitely something to them. The health benefits of relaxation [40] and pleasure-seeking [41] are not to be understated.

That’s it for today, folks. Thanks for reading!