Dear Mark: Wheat and Asthma, Minimalist Winter Shoes, High-Fat Rat Cognition Study, and Sun Exposure Timing

Today’s edition of “Dear Mark” runs the gamut. The topics will be somewhat familiar, since I tackle wheat, minimalist shoes, high-fat diets in the news, and vitamin D, but with interesting spins on each. First, I discuss the link between wheat and asthma. Next, I do a somewhat exhaustive search of the available winter minimalist shoe options, a topic that I’ve never had cause to explore for myself. Since I do this for you guys, though, I tried to help out. After that, it’s my quick but (in my mind) pretty conclusive take on the latest article to pin cognitive decline on a high-fat diet for a reader who’s dealing with a similar condition herself (or himself; the gender of the name “Jo” is somewhat ambiguous). And finally, I discuss whether or not there’s a best time of day to obtain vitamin D from the sun.

Let’s get going:


I love the website and your books. I have been eating paleo for the past 4 months and notice a huge difference in my athletic performance and general out look on life. I have suffered from asthma my entire life. After eating a sandwich made with french bread (refined wheat) or a plate of pasta (which is rarely now), I find my breathing slightly labored even while sitting. Is there any research supporting the removal of gluten and wheat help asthmatics?

I would love to know you thoughts…


I think so, yes. Something called baker’s asthma, which has been identified since at least the 1700s and is exactly as it sounds, is linked to the ingestion (this time via the clouds of airborne flour to which bakers are constantly exposed) of gliadins, the protein subfractions that make up gluten.

There’s also a related condition called wheat-dependent exercise-induced anaphylaxis where wheat-related proteins make it through the intestinal wall into the blood and cause an immune response that manifests as an asthma attack. It’s “exercise-induced” because exercise seems to speed up the rate at which the wheat gliadins make it into the blood, but even those at rest had evidence of an immune response to the gliadins.

There’s also evidence of plain-old wheat-induced asthma – no exercise necessary.

I’d say you’re on to something, Drew. You can keep experimenting if you like, but I’d suggest just staying away from the stuff myself! Good luck!

Hey Mark. I’m very addicted to my Vibrams, and with this nor’easter coming through I had to go back to my winter boots, and while they do keep me dry and warm, I’m hating it!

Tried looking through the site but didn’t find anything as far as some type of minimalist shoe for winter? Any recommendations?

Wish Vibrams made a winter type shoe. I see they used to make one that kind of looks like it would be helpful, but they don’t sell it anymore.



I share your addiction. For folks who actually have real seasons with a real winter, the minimalist winter shoe is something of a white whale – an enigma hovering just out of reach, a product that you know should exist but that you can never actually pin down. I’ve never really looked into it for my own feet, since they rarely see cold weather, but let’s see what’s out there, yeah?

First, a quick glance at the minimalist wintery offerings from the well-known companies out there:


Men – Nothing meant for winter that I could see.

Women – Barefoot Life Frost Glove: waterproof, insulated, Vibram sole.

Vivo Barefoot

Men – The Off Road Hi and Off Road Mid look to be decently protective options.

Women – They’ve got an entire winter boot collection for women, albeit a fairly small one.


Unisex – Adult Phoenix Boot: sheepskin lining, 5 mm Vibram sole, lighter and more flexible sole as of 2012, roomy toebox (very important, in my experience, for true barefoot feel), naturally water-resistant.

Now, how about the shoe options that might not be officially minimalist but are close enough?

Russel Moccasin now makes a full lineup of minimalist moccasins, some of which are winter proof. They’ve been around for decades, so they should be pretty high quality.

Otz Shoes has a Troop Boot. It’s not billed or promoted as minimalist, but as this review from Birthday Shoes suggests, it can certainly be modified to become an effective, minimalist winter boot. They’ve got ’em in women’s, too.

There’s an actual minimalist army boot out, as well – the Belleville Minimalist Training Boot. Read the review.

O’neill (yes, the surfwear company) makes a neoprene reef boot. Since it’s designed for water sports, it’s fairly water-resistant, and since it’s designed for cold ocean water, it’ll keep you warm. It’s also got good grip and the price is fantastic.

If you have a favorite barefoot shoe that isn’t quite protective or warm enough, you can always throw some overboots over your boots (or shoes). They work on hiking boots and shoes equally. Here’s another link. If you really want to stick with the FiveFingers and somehow stay warm, you could always wear them with some outdoor toe socks from Injinji.

That should do it. I hope you find something amidst all those links that works for you.

Hi Mark,

I’m an international fan — I live in Korea and have been reading your blog since February 2012. I first saw Dr. Terry Wahls’ TED talk “Minding Your Mitochondria” online, then went on vacation to Vietnam, where another tourist from Romania shared your website with me. So you have quite the far-reaching influence, and I now regularly quote you to friends from Korea, Canada, the US, and France, proselytizing as many as I can! 😉 I even try to raise primal-related questions among my students at Seoul National University, where I teach English for Academic Purposes.

Anyway, I also happen to have been diagnosed with MS (technically Clinically Isolated Syndrome), but to make a long story short, although I recovered nearly fully from my first severe attack before going primal (basically by unwittingly doing everything in the primal lifestyle except the diet bit), I have felt even better since going grain- and refined sugar-free, and my most recent MRI even indicates likely re-myelination of the lesions in my brain.

So naturally, when I saw this article on the NY Times today – Can Exercise Protect the Brain from Fatty Foods? – I was skeptical, given that I have been eating a high-fat diet and have simultaneously (if not causally) seen “improvements” in my brain. I wondered what actual foods, in both the high-fat diet and the “conventional” one, they were feeding their lab rats, and if there is a chance that a high fat diet could, in fact, damage the brain. My personal guess is that it really depends on the type of fat…I would love it if you could share your take on this study.

Thanks for all the work you do,


Browse the comment section of that NY Times article and you’ll find that one commenter (Edward Barton) contacted the study’s lead author and found out that the fat in the diet “consisted exclusively of commercially produced (soy and corn derived) lard and soy oil.” As we now know, the lard used in refined lab diets is far higher in omega-6 than previously thought due to the modern pig’s usual diet, which consists of mostly corn and soy products. If you look at the USDA nutritional database, lard is pretty high in monounsaturated and saturated fats and low in polyunsaturated, but the actual lard used in lab diets contains twice as much PUFA.

Does this matter? I think it might. Previous studies have shown that among polyunsatuturated fats, only DHA, EPA, and arachidonic acid increase membrane fluidity in the brain while linoleic acid failed to increase it, a significant finding for two reasons. First, patients with Alzheimer’s disease tend to have far less membrane fluidity than control patients, and a fluid brain is required for optimal cognition. Second, the added PUFA in the industrial lard is almost entirely linoleic acid (not arachidonic acid), which the pigs obtain from the soy and corn in their diets and incorporate directly into their adipose tissue. If these rats were on a high linoleic acid diet – which they undoubtedly were – we would expect membrane fluidity and cognition to be impaired. No real surprise there.

Besides, you’re not a rat, you’re not eating rancid refined lard and soybean oil high in omega-6 fats, and you’ve actually made progress against your condition. I wouldn’t worry. It’s not like your brain’s apparent re-myelination is merely a feint in the right direction before it begins backtracking toward progression of the disease. Even if the mice were on a rodent version of a Primal eating plan, I wouldn’t worry purely on the strength of your own response to the diet and lifestyle changes. Heck, even if you were a rat that had somehow gained the ability to send emails and compose thoughtful, cogent prose, I’d say you should stick with what is obviously working for you even if the high-fat lab diet wasn’t working for your fellow rodents. The proof is in the pudding, especially if the pudding is in your bowl.

Mark, I have read your book. What time of the day is best for the skin to create vitamin D from the sun?


Great question. The skin will make vitamin D from UVB exposure at whatever time of the day it receives it, so the real key is figuring out when UVB is out and about. That depends on where you are and what time of the year it is, of course, but for the most part, UVB peaks at solar noon, or whenever the sun is highest in the sky. If you’ve got a short shadow and the UV index is high enough, you’re probably making vitamin D.

However, there are other things to consider. Now, you may have gotten the impression that the sun is wholly our friend, that it can do no wrong, that skin cancer from too much sun is a myth. It’s not. The sun can damage our skin and, if enough accrues, it can cause cancer. Significant evidence from animal models suggests that sunning ourselves at the wrong time of day can make us more susceptible to skin cancer (PDF). To protect our skin from UV rays, we manufacture an endogenous compound called xeroderma pigmentosum group A, or XPA. XPA plays an important role in the repair of sun damaged skin, and it follows a circadian schedule. In other words, XPA isn’t just produced when you need it. It peaks at certain times of day. In mice, XPA peaked at 4 PM and dropped off at 4 AM; exposing them to UV at 4 AM gave them cancer fives times more frequently than exposing them to UV at 4 PM. For humans, XPA peaks in the morning at around 7 AM.

So, you can make vitamin D whenever the sun is strong enough, but you might want to consider your XPA levels, too. The rodents’ levels peaked at 4 PM and dipped immediately after, but they were still significantly elevated at 9 PM and totally tanked by 1 AM. If our XPA trajectory is similar, we should enjoy the most protection between 7 AM and noon, with the former time obviously offering the most protection. It’s also conceivable that all this gets thrown out the window if your circadian rhythm is messed up for whatever reason. Something to keep in mind, at the very least.

Hat tip to Jamie Scott for his excellent take on the paper.

TAGS:  dear mark, gluten

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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