Dear Mark: Egg Shell Calcium, Fully Hydrogenated Oils, HG Walking, Gorging, and Frozen Produce

This was a crazy week, eh? I offered up a brand new book and an accompanying special offer, and you guys responded. Although I’m not sure if we sold enough copies of The Primal Blueprint 21-day Total Body Transformation to make the New York Times best seller list (we’ll see and my fingers are crossed), I know it will changing many, many lives. And regardless of the ultimate outcome, I just wanted to thank you all for your support. I couldn’t – and wouldn’t – do it without you.

Anyway, it’s Monday, and that means it’s time for another round of “Dear Mark” questions-and-answers. We’ve got a good one on fully, as opposed to partially, hydrogenated oils (and the answer may surprise you). I cover homemade egg shell calcium supplements, average hunter-gatherer walking distance, the place of gorging in a Primal eating plan, and whether frozen produce retains sufficient nutrient content when compared to fresh. Let’s go.

Hi Mark!

Thank you so much for your life-changing work. You’ve written about calcium before, but I wanted to see if you had an opinion about eating eggshells. Yes, eating eggshells! I eat primally, and I know the importance of calcium is overstated in the conventional wisdom, but I’m still concerned that I don’t get enough calcium. I know some folks pulverize eggshells and then liquefy them with something acidic like vinegar or lemon juice, then down them, to get calcium from a natural source. It seems like the kind of hack that would appeal to us primals…do you think doing this is a good idea?


Sure, eggshells are a great source of calcium carbonate that turns into calcium citrate if dissolved in an acidic medium (this seems like a good recipe). I don’t do this myself, but I’ll sometimes supplement Buddha’s (my dog) meals with a half teaspoon of powdered eggshell if he’s not getting much bone that day. Dogs need a lot of “bony” material – bones, cartilage, etc. – and eggshell’s a worthy replacement. If you need bony material, I’d say go with eggshells.

Just be sure you’re using high quality eggs – preferably pastured – from a farm you trust. A better egg from a chicken on a better diet will have more calcium and other minerals in the shell, making it worthy of the time and effort required to render it consumable and digestible. The pastured eggs I get require a couple solid whacks to crack open because they’re so dense. If you recall from an older post on pastured v. conventional eggs, pastured (that is, eggs from chickens allowed to roam around, eat bugs/mice/lizards/wild seeds/grass, and get into trouble) eggs were far more nutrient-dense than conventional eggs. I imagine the same advantages are borne out in the shell of a pastured egg.

I wonder what the average distance covered by a hunter gatherer to and from their homes was? How much walking, lifting, picking, climbing, moving, was the daily average?


Great question! We obviously have no way of knowing how far our paleolithic ancestors walked or how often they lifted/climbed/ran on a daily basis, but we can get some clues by looking at ethnographic studies of modern hunter-gatherer groups. Let’s look at one of the best-studied, the Hadza:

In “The Hadza: Hunter-Gatherers of Tanzania,” Frank Marlowe, who spent four years with the tribes, writes that foraging Hadza women walked an average of 5.5 km a day at 3.5 km/hour and foraging men walked an average of 8.3 km each day at 3.6 km/hour. Able-bodied adults foraged on a daily basis, so that’s a lot of slow moving. As those are just averages, however, some forays were longer and some were shorter. The women Marlowe observed walked anywhere from a quarter kilometer to thirteen, while the men walked as little as 1.57 km and as many as 27.2. It changed, day to day, and that’s the whole point. It was never the same. It was always something new. Physical activity came in peaks and valleys, because that’s what the situation demanded.

Contrast that with today, where we get our food by walking (or driving) to the store. A brick-and-mortar store that never changes locations, never runs out, and always stocks the same food. The Hadza, and all other hunter-gatherers throughout history, had to chase, climb after, search for, dig up, discover, and even go without their food. They might get lucky and find a stash of tubers or an acre of berry bushes located a half mile from their camp that would sustain them for a couple weeks, or they might go out for what they assumed would be a short, easy hunt and end up spending two days and twenty miles stalking a particularly fatty bull. Either way, they engaged in a ton of low-level activity. That much we can safely say.

All the information I find on your site talks about “gorging” as a bad thing; that the human urge to eat everything in sight is something to be avoided.

But couldn’t we look at this as a primal queue? i.e. if Grok had a fresh kill and was very hungry, wouldn’t he have completely gorged himself? Shouldn’t we follow suit and occasionally stuff ourselves beyond satiety on something like good organic grass-fed meat?


It’s not that gorging is bad, in and of itself. It’s just that the way most people gorge – at Chinese buffets, also known as oxidized soybean oil troughs; on late-night post-bar dollar menu runs; as a steady trickle of office snacks throughout the day that’s more like an epic Roman feast without the strategic vomiting than any definition of snacking I’ve ever seen – (and especially what they gorge on) is bad. I actually like a good gorge every now and then (though I usually abstain simply because post-gorging is often uncomfortable). If you stick to the right Primal foods, and make sure you’ve earned it (a fast, a heavy lifting session, you just cooked the most amazing roast chicken and you can’t bring yourself to leave it unfinished), go ahead and pig out. Just don’t make every meal a feast.

Satiety is a murky concept that’s always changing. Satiety is contextual. If I’m coming off a 24-hour fast, my idea of satiety might involve some heavy breathing at the end of it, perhaps even a bit of regret. Then again, I have a good handle on my hunger. It doesn’t control me. It comes at a reasonable time, I respond by eating something, and it goes away until it’s time to come again. My hunger isn’t constantly texting me, or poking me on Facebook, or loitering around outside my house, or anything like that. No, it arrives at almost exactly the right time, every time.

If you have that kind of relationship with your satiety signals, go ahead and indulge every now and then.

Dear Mark,

We’ve had a few emails in the past, though I’m sure you get tons every day. I’ve been primal for 2 years (age 23), and it’s a wonderful change from the 3 years of vegetarianism I had before hand. I’m currently in graduate school working on getting into medical school.

Here’s something I just came across in biochemistry that I thought was interesting:

In discussing the hydrogenation of unsat. fat, we learned that full hydrogenation yields a completely sat. fat, it appears that only partial hydrogenation gives rise to trans fat. I’m sure it depends on the length of the fat, but typically stearate is the result of complete hydrogenation, which is a C18 and can be metabolized. So, based on that, is a fully hydrogenated fat all that bad?

I’m sure most of the foods that use such fat as an ingredient are negated by the rest of the ingredient list, but I just thought it was an interesting piece of information.



I (and many others, I think) have a knee-jerk negative reaction to the word “hydrogenation,” but a fully hydrogenated fat is indeed fully saturated stearic acid. In fact, some studies even use fully hydrogenated oils to examine the effects of stearic acid, like they do here. Using fully hydrogenated soybean oil as the stearate, the authors found that a high intake of stearic acid lowered LDL cholesterol to a greater extent than either the palmitic acid or oleic acid diets.

On the question of digestibility/metabolization, there is this: a study found that rats digest fully hydrogenated oil quite poorly. Whereas they could assimilate between 94-98% of the soybean, medium chain triglyceride, and hydrogenated coconut oils, rats were only about to digest about 30% of the fully hydrogenated soybean oil. Fully hydrogenated soybean oil-fed rats produced three times as much fecal matter, and something tells me those weren’t your typical well-formed and firm rat droppings. Of course, the study’s authors tout this as a “potential benefit” of fully hydrogenated oils.

But then there’s also this: a study (PDF) in which rats fed cocoa butter, rich in stearic-acid (the saturated fatty acid that fully hydrogenated oil becomes), also had trouble absorbing it. The stearic acid in cocoa butter is natural, not industrially-induced, and it still had the same effect in rats. It looks like it’s the stearic acid to “blame,” not the hydrogenation.

As Dr. Michael Eades is fond of saying, rats are not furry little humans. I’m still not eating the stuff, but from an objective analysis it’s probably safer than partially hydrogenated fat.

Hi Mark,

I was wondering what your thoughts are on the nutritional value of frozen fruits and vegetables (really I’m more concerned about fruits, but I figure the two go together). The reason I ask is that the fruits in my local area suck, even at the farmer’s markets and Whole Foods. Almost all of them are either under-ripe or rotten. Also, the cost seems extravagant for the terrible quality. From what I’ve read frozen fruits and veggies tend to be “flash frozen” at their optimal ripeness and, because of this, can preserve more nutrients than “fresh” fruits and vegetables. Is this true, or just another marketing gimmick?



Rather than opining or trusting marketing, let’s take a look at some research:

In raspberries, flash-freezing only “slightly affected” ellagic acid (an antioxidant), phenolic, and vitamin C content, but after a year in the freezer, ellagic acid and vitamin C levels were 14-21% and 33-55% lower, respectively. Fresh fruit won out in the study, but “just frozen” was right behind it.

You’re mostly concerned with fruits, but what about vegetables? Another study compared fresh to frozen vegetables for vitamin C content, including spinach, broccoli, peas, and green beans. Frozen generally performed well against fresh, scoring only slightly lower than freshly harvested vegetables. These were straight-outta-the-ground fresh, however; the authors note that frozen vegetables bested standard grocery store fresh produce quite handily.

The research is very consistent. If you can’t get decent fresh produce, frozen is totally worth it – and sometimes superior to “fresh” produce that’s been sitting around the store for awhile. I myself always keep a few bags of frozen blueberries, raspberries, and strawberries on hand. I’d keep blackberries, but I’ve never found a good frozen blackberry.

Whatever you do, make sure to lick the bowl if you let your frozen blueberries thaw. Anthocyanin leakage is very real.

Thanks for reading and asking, folks. Keep the questions coming!

TAGS:  dear mark, Grok

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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