Dear Mark: Dehydrated Vegetables, Cooked Versus Raw, and Premature Graying and Copper

Vegetables can be hard enough to work into our diet without other factors making it even more difficult. Either we’re stuck with nutrient-sparse, weeks-old produce that has lost all semblance of flavor (but it’s certainly affordable!), or we’re inundated with a countertop full of beautiful vegetation straight from the farmers’ market that we can’t hope to consume in time. You think convincing a ten year old to eat a plate of fresh sauteed kale is hard? Try getting a ten year old to eat a plate of sauteed withered kale that’s been sitting in the fridge for a week. And what about cooked vegetables versus raw? Some say that raw produce is the only way to eat it, that if you cook a carrot you’re rendering its nutritional content null and void. Is it really that dire? Does it matter that much? Find out the answers to these questions, plus one on whether or not copper deficiency can trigger premature gray hairs, in this week’s edition of Dear Mark.

Let’s go.

Hi Mark,
I have checked some of your older posts for info and maybe I’ve missed it, but I was wondering about the nutritional value of dehydrated veggies. I know that when you eat dehydrated fruits (apple rings, banana chips, craisins, etc.), you are primarily eating sugar. What happens to veggies when you dehydrate them? I was thinking that some fun snacks would be carrot or zucchini “chips” for my kids. I found the recipe you posted for Diana’s zucchini chips, but how does the nutrient profile hold up? Do some veggies hold up to dehydration better than others (nutritionally speaking)?


According to one source on dehydrated vegetables, vitamin A is mostly retained, vitamin C is mostly lost, B-vitamins are somewhat reduced, and minerals are lost only if you hydrate the vegetables and discard the soaking liquid. Since you’re going to be eating the vegetables directly rather than cooking with them, you don’t have to worry about that. As I mentioned in a past Dear Mark that dealt with powdered, dehydrated green drink smoothies, dehydrated vegetables may lose some of the volatile nutrients (like vitamin C and the carotenes), but many more are retained, and even when you lose some nutrients you’re not losing all of them. Eating a dehydrated vegetable chip is going to be better than eating nothing at all.

Methods matter, of course. Air-drying, which most home dehydrators employ, results in more nutrient loss than vacuum drying and low-pressure super-steam drying. Using a lower temperature, even if you’re going with an air-drying dehydration process, will be gentler and therefore preserve more nutrients than using hotter temperatures.

Traditional sun-drying might have different effects. In one study, sun-drying greatly reduced the vitamin C content while increasing the antioxidant capacity, phenolic content, and free-radical scavenging ability of leafy green vegetables common to Nigeria. If you recall from my post a ways back on hacking the vitamin content of your produce, exposing green produce to artificial lighting (like you’d get in a supermarket) increases the phytochemical content of that produce. Perhaps sun-drying – which uses a far more powerful light source – confers similar benefits?

Overall, dehydrated veggies are a good option. Most of the important stuff (minerals, antioxidants) will be retained, as long as you’re gentle with your drying.

Hello Mark,

For breakfast I throw a good amount of peppers, onions and mushrooms in the skillet with olive oil to eat with my omelet. Is it ok to “fry” my veggies this way or should I just eat them raw? I do this because they taste better.


Don, I’d just say go for it and keep doing what you’re doing, but I know it’s fun to geek out a bit on this stuff from time to time. If you want to get nerdy about it, we can go through each vegetable and see how cooking does, or doesn’t affect the nutritional value. Shall we?


Raw onion is more effective at inhibiting platelet aggregation than cooked onion. Another study had similar results. In other words, both raw and cooked onion make your blood less “sticky,” but raw onion is better at it. Point to raw.

Onions sauteed in oil show a 7-25% increase in quercetin concentration (a powerful antioxidant) levels over raw onions. Point to cooked.

Sauteeing onions preserves more antioxidants (they “remained high” when compared to raw) than frying onions. Point to cooked (sauteed, specifically).


Compared to boiling or steaming, stir-frying without water is the optimal way to cook “colored peppers” and retain their antioxidant content. Point to cooked (sauteed, specifically).

In another study, grilling colorful Mexican peppers over open flame caused the largest increase in phenolic content, though spiciness (read: flavor) remained similar in grilled, boiled, and raw peppers. I’d say that grilling is pretty similar to sauteeing; wouldn’t you? Point to cooked.

Peppers are a rich source of vitamin C, but cooking can reduce that. Since you’re sauteeing for a short period of time, rather than boiling, the losses should be minimized. Still, it’s something to consider. Point to raw.


Though boiling mushrooms results in a significant loss of selenium (to the water), other forms of cooking (like sauteeing in a pan of olive oil) probably do not. Technically, point to raw (but you’re not boiling).

Another study (PDF), this time on Thai mushrooms, confirms that boiling negatively affects the antioxidant activity and polyphenol content, but that by consuming both the mushroom tissue and the boiling liquid (or broth) the lost nutrients can be salvaged. Again, you’re not boiling, so this may not even apply. Point to raw.

I would eat at least some of your produce in the raw state, just for variety and because it could be a good way to eat some dirt (as long as you’re getting produce from a farm you trust), but for the most part, you’re going to be just fine cooking your vegetables.

Dear Mark,

At the ripe old age of almost 28 I’ve been noticing a few gray hairs – mostly on my chest. I’ve heard that graying hair can be a sign of a copper deficiency, so I’m left to wonder what foods I might be lacking?  Or is this really just a matter of the genetic lottery?



You might be on to something. There’s a rare genetic condition called Menkes disease where a mutation disrupts the normal distribution of copper to surrounding tissues, thereby turning the hair gray (among other effects). It’s quite deadly, and autopsies of people who had Menkes show a total lack of copper in their hair. Menkes is also called “steely hair disease,” owing to the premature graying it causes. I’m guessing you don’t have Menkes, because you probably wouldn’t have outlived infancy. A study from this year shows that gray hairs from people suffering normal, premature graying also contain less copper than normal colored hair from the control group. Similar relationships for iron and zinc were not found.

Though the only way to really know if a copper deficiency is causing your graying would be to get your gray hairs tested at a lab for metal content, you could try adding in some copper-rich foods to your diet to see if they have an effect. Beef and lamb liver are the best sources of copper, but a little bit goes a long way. Other good sources include oysters, crimini mushrooms, and dark chocolate. Maybe plug your weekly food intake into a tracking program to see if your copper is low. You’ll want about 2 mg per day, but you don’t have to do it piecemeal. A half pound per week of beef or lamb liver all at once should get you there.

It might also be worth looking at whether your zinc intake is outpacing your copper intake. Zinc and copper compete for the same pathways in the body, so an excess of one could lead to a deficiency of the other. Chris Kresser just did a podcast on this subject, although he was looking at it from a standpoint of excessive copper and inadequate zinc.

That’s it for this week, folks. Keep sending in your questions and I’ll keep answering them. Take care and 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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75 thoughts on “Dear Mark: Dehydrated Vegetables, Cooked Versus Raw, and Premature Graying and Copper”

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  1. Slightly off topic:

    Does anyone know the evolutionary benefit of grey hair upon aging? Been looking for an answer only to find things like, “Because hunter-gatherers never lived past 25!!!” Which I know not to be true.

    1. There probably isn’t any. Just because something happens doesn’t mean there is any benefit, evolutionary or otherwise, to it. If gray hair is indeed a sign of copper deficiency, it’s a sign that’s something is wrong.

    2. It could be a sign of maturity, which would indicate both quality as a mate (in a selfish gene sense) and amassed intelligence and experience (in a cultural sense, which I think is just as important to human evolution as pure natural selection on alleles)

    3. It marked us for the saber-toothed tigers. “Hey, this one’s ready!”

      1. Nah, grey hair means we are tough and stringy! So there ya go, that’s the evolutionary advantage. lol

    4. From a natural selection or sexual selection standpoint, a characteristic can be passed on if it doesn’t lead the organism to be killed off before reproductive maturity is attained. Like John pointed out, graying may not confer any benefit–it may just be.

  2. I started to grey at 19 or 20. I have quite a bit now at age 33. But so did my dad at the same age. I assumed it was simply genetic, but maybe there’s more to it. I never eat the things listed, so perhaps I should tart now. It’d be a lot better than usung air dye like I do ow!

    1. I eat plenty of dark chocolate and the gray hairs are still coming on, so I’m doubting the copper deficiency theory. I have read that supplementing with blackstrap molasses every day will stave off or even reverse gray hair growth. Anyone ever try that?

      1. I believe the blackstrap molasses has copper in it. But watch out, it can also cause some soft stools. lol

  3. I have heard that supplementing with nutritional yeast can circumvent/prevent graying, true? Also heard it can help keep the wig tight.

  4. Has anyone else noticed that a lot of vegetarians and vegans get grey hair really young? They most certainly aren’t eating liver, and probably don’t eat a lot of oysters, either. I’m guessing that overall, most vegetarian staples aren’t great sources of copper, right?

    1. Yes, I have noticed that! You can usually tell when someone is vegetarian or vegan, just from the hair.

    2. I was a vegetarian for 35 years, I am now 71 and only recently started getting some grey hairs. Mostly at the temples. My 75 year old sister who smokes, drinks and has MS has even less grey hair. My mother at 90 was salt and pepper, not totally grey. Genetics I am guessing.

  5. I am super curious about the premature greying. I started going gray around 25, and now at 32, it is pretty pronounced. I don’t dye my hair, but it IS hard to make peace with sometimes. For the record, I definitely put away my share of dark chocolate on a regular basis!

  6. I’ve got the George Clooney thing going on so I’m fine with the grey in my hair.

  7. Great info. Fermenting some mustard greens today and the recipe calls for wilting the greens in the sun before salting and packing them. I’ve never had the opportunity (welcome to Washington!) but will be in the lookout for the chance this summer! Ultra Mega Super Greens!

  8. I also pursued that copper connection for grey hair because I couldn’t explain the increasing weirdness in my beard hair. Starting in my early 20s quite a lot of the strands were coming in grey, or in in-between colours like orange or yellow. Many more have have a series of kinks, changes in thickness, and broken filaments hanging off.

    Increasing copper didn’t seem to help. Right now I’m doing some anti-candida treatments to see if that helps (I’m fairly certain I do have a problem with too much systemic yeast). Reportedly that can also lead to grey hairs, although I’m not sure about the malformed strands.

    1. That sounds like me.
      I always wondered why some of my hair strands are malformed and have kinks, while the rest are stick straight and soft.

      I found my first grey (or better said WHITE) hair at age 16.
      The hair that’s formed my life long cow lick is now white at age 41, while the rest are still my regular dirty dishwater color…it sucks.

      Whoever invented hair color was a genius 🙂

    2. I love my grey hair–it has so much variation in color. It is normal for grey hair to be curlier and coarser than the straight hair it replaces. I got my first grey hairs early but it has progressed more slowly than my mother or grandmother. They both liked liver, oysters, and dark chocolate so I doubt copper is making the difference.

  9. If genetics are not the sole reason I think imbalance might be the key. Doesnt Green Tea promote increases in zinc, and would therefore increase a zinc/copper imbalance? There has been a lot more green tea consumption and a lot less lamb liver consumption these days.

  10. Is grey hair the human equivalent of dominant male gorillas becoming “silver backs?”

    1. YES!!!! I am more of a “dominant” myself 😉
      eh, I love my silver. I started turning grey slowly about 19. Then the pace quickened in my 40s. Just like both my parents & my sister. My brother is the “rogue” & is only lightly grey.

    1. The other day some dark chocolate rescued me from a burning building just after it helped an old lady cross the street. Truly amazing(and delicious)stuff.:)

      1. What kind was it? Xocai just got the patent to call our chocolate The Healthy Chocolate. It is the number 1 anticoxidant superfood in the world. It is amazing. Now not only can we be healthy, why not wealthy as well. Ask me how.

    2. I agree with that and chocolate is cheaper than therapy. If you want information on how you can get The Healthy Chocolate (xocai) please email me! I can show you how you can be healthy and wealthy (if you wish!)

      1. Xocai is WAY too expensive, they totally need to come down on their prices.

  11. Regarding hair: Steve Martin seems to be aging quite well at 66, and he’s famously had gray hair since his 20s.

  12. What a timely post ~ I just ordered two books on dehydrating! I’m gearing up for an abundance of wonderful garden-fresh food from my local CSA (as well as overflow donations I often get from friends who garden).

    On another note, I’ve been looking high and low for a good, informative resource on sprouting and fermenting. I have no interest in growing wheat grass (we’re a gluten-free house) but I would like to know how to sprout legumes (lentils, black beans, chickpeas), some nuts like almonds, and a few select non-gluten grains. I can’t find really clear step-by-step instructions anywhere, just warnings about issues like mold and fungal contamination that can occur (but no info on how to minimize these risks). I want to prepare these things using traditional methods (soaking, sprouting, fermenting) to improve their nutritional quality when we do eat these things (sparingly) but where is the info?? Any ideas from the Grokdom?

    1. steve meyerowitz (aka “sproutman”) has books and supplies for sprouting all kinds of things. google “sproutman” and you should be able to find him.

    2. What grass is not a gluten-containing plant. Please do your research and see for yourself.

  13. Our daughter was 3 years old when I found a grey hair growing near the nape of her neck. It was novelty! She is now 5 and I periodically check to see if it’s grown back in. It hasn’t yet.

    My hubby, her dad, has been greying since he was a teenager. But 3 years old? That’s crazy!

  14. I’d like to mention that premature greying can also be cause by mild Vitiligo. It runs in my family. Everyone else got skin patches except me, I got a wicked cool silver hair streak. It’s been getting bigger since i was 17; now at age 26 it’s quite a noticeable silver streak.
    Also certain types of anaemia, but that’s not likely in Paleo communities! lol

  15. …. just a note about copper – various forms of it are used quite heavily in the organic produce production cause it’s one of the few compounds that are allowed for the organic farmer for some pretty tough fungi and buggies – if you eat organic and have been lax about washing your veg – you may be running the opposite problem with copper – and getting overloaded –

    wash the veg – organic ones too–

  16. Speaking of vitamin a and veggies, I was under the impression that only animal foods contained REAL a…. since only about half the population is adept at converting beta-carotene to a, it’s inadvisible to count on getting your a from veggies anyway! 😉

  17. Grey hair = wisdom
    And I’m pretty sure dark chocolate harnesses the same powers as a good cup of tea. Turns days around for the better, and puts a smile on the dial.

  18. I grow coloured sheep here in Australia. In some districts, notably around South Australia, the tradition amongst white merino farmers was to run a coloured sheep with the white flock. If it’s pigment changed or even went white during it’s growth then the producer would supplement copper to the flock. The handle of the fibre would change with the crimp disappearing and it would feel harsh. Old timers would call it steely wool. In my flock I notice changes very occasionally, usually with sickness or shock which could cause a break in the wool and sometimes a colour change. Most of my very dark animals lighten up over the years, so I reckon it’s a bit of column A and a bit of column B,

  19. Some say you can delay going grey through daily practise of yoga inversions like handstand, headstand, shoulderstand, viparita karani etc. The theory is that these poses stimulate blood flow to the hair follicles. The increase in blood flow to the brain and face also apparently improve memory and concentration, and reduce wrinkles.

  20. Every morning I stir-fry some leafy greens I have around (spinach, raab, kale) for breakfast… you should leave them in the pan until the colour turns to dark green (~1 min.). Doing so you mainly disrupt cell walls and render nutrients more bioavailable while retaining almost all of them. And don’t forget that they also get juicy so you kick the taste a bit and you can actually enjoy them!

  21. Iodine is another mineral that is supposed to improve hair quality (and sheep’s wool I gather).

  22. I come from a long line of redheads on my moms side and some native American on my dads. No one on my dads side ever developed much gray. My moms side “went pink”, to quote my grandmother. Oddly, I am mostly platinum blond, now, at 53. I feel pretty lucky, though. Both of my brothers are mostly bald. I can’t use hair color because it causes my hair to break off or fall out. I’ve never been a vegetarian, but I haven’t eaten much meat until recently. The good news is that, since I’m a brunette, I haven’t faded to pink. Nor am I bald. Life is good!

  23. This isn’t exactly on point, but I recently learned that putting wilty green veg in a bowl (or sink) of cold water with a little white vinegar will perk them back up again. Might help with the picky kids.

  24. I have read that gray hair is directly related to low/not optimal stomach acid. What I read is that low stomach acid does not allow your body to access the nutrients the way it needs to and as a result your hair’s color/graying is a sign of not enough nutrients available to your body. Can’t gaurantee it, but made sense when the author laid it out (I think the book was “green for life” about incorporating green smoothies into your diet). Take it with a grain of salt.


  25. Interesting info on copper. Anne Louise Gittleman (who has some crossover with Paleo recommendations though also diverges) indicates that many people actually suffer from copper excess and zinc deficiency:
    It’s so hard to know what to do, even when trying to stick to “keeping things simple” and monitoring your own body.

  26. I started going grey when I was 18. My whole family goes grey prematurely – My brother was totally white at 30. For me its definitely a genetic thing.

    I have battled it with “the bottle” until going primal. I figured what was the point of cutting out all processed food etc, if I was still putting poison on my head.

    I am now 46 and growing my dyed hair out – I am totally white in front and a steel grey colour in back. I find myself feeling really great about my new hair colour – because its been hidden for so long under the fake stuff. Its about finding my true self and fits well with my primal thinking.

    If there were more women around who were young (or youngish) and proud to be silver we wouldn’t be such an oddity. plus – particularly dark hair dye is extremely carcinogenic.

    Ladies dont be one of those older ladies with fake looking dyed hair – check out – and own it!

  27. Mark,
    Zinc supplementation depletes copper. The recommendation is that if you’re supplementing with zinc, you also supplement with copper in a 15:1 ratio of zinc to copper.


  28. Regarding,
    “Sauteeing onions preserves more antioxidants than frying onions.”

    Whats the difference in Sauteeing & frying? The amount of time in the pan, or the frequency at which you move it?

  29. At almost 57 I have very little silver hair. Yes, it’s shiny silver in the sunlight rather than gray ; ). My 1/4 Native American grandma had very dark hair through her 60’s but she also had nice pigment in her skin unlike my pale Irish looking self so I didn’t expect to get the benefit of delayed graying but I’ll take it. I’ve done searches trying to find out why but still unsure other than genetics. Until less than a year ago my diet was on the worst side of SAD but I do like my chocolate and sunflower seeds are a favorite snack, supposed to have a decent amount of copper?

  30. This topic’s interesting to me because I’ve had a reversal of graying hair in the last 6 months. I had a strong streak of gray and gray hairs all throughout my light brown hair. It was noticeable, and kind of pretty, in its way.

    My little daughter asked where they were all going, and I had to look. There are many fewer! One would not look at me now and say I’m graying. What’s different: green tea, eggs, lightly steamed broccoli and a little fruit every morning since December 1. Paleo/primal eating overall, fewer sweets except for Ethereal Confections chocolate. Some broth, lots more meat and even MORE fresh veggies. Tons of greens: kale, beet greens, green leaf lettuce every day. Used to be rare. Elimination of a hugely-carb diet. Much less chronic cardio, more lifting and lots of pullups. And SLEEP.

    I fullu expect to continue graying at some point. However, this reversal at age 46 has me interested. Wasn’t looking for it, but it has happened. I changed so much about my life from mid-November that I don’t know what the cause is.

  31. As for the greying hair…

    I started going grey early for my family and by my early 40s I had definite streaks at both temples, and with long hair in a bun, ended up with a subtle candy cane type effect. Shortly after that as more grey came in and the brown hair turned to a dead, dull, mouse, I discovered the joys of red hair, which my husband loves. I have noticed though since I started going primal (not all the way there, but much, much, better than I was eating a year ago) that my roots seem to have a lot less silver than they used to.

    I also had classic mittleschmerz cramps last month, after having been officially postmenopausal for over two years.

    I’m going to attribute both to just better nutrition overall.

  32. Never heard the copper connection for gray hair, but my aunt (a redhead) always said it was a lack of iodine that led to gray hair. Don’t know of any scientific proof, but she passed on at 92 with only about 25 gray hairs — her red did become slightly less vivid though after her 80th birthday. Her sisters both got grey in their forties, so maybe she was on to something?

  33. What are your thoughts on an entirely raw diet? Isn’t this the most primal you can get?

  34. ?????????????????????????????????????? ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

  35. What about the effects of stress on grey hair? I’ve noticed I get grey during particularly stressful times of life. Is there something to this folk wisdom?

  36. ?????????????????????????????????????1???????????????????????????????? 2011/2012 ?????????????????????????????????????????????????????????????1???????

  37. Re greying hair – both my brother and I lived in Los Angeles (he for nearly 20 years, and I for nearly 10). We both noticed that our hair was really turning grey. We both recently moved to Florida and, after only a year, both of us have our natural hair color back – the greying has predominantly stopped.

    I never wanted to live in L.A. because I knew it was toxic there (had to move there to help out my family); and this was just one of several things that convinced me that Los Angeles is doing things to people that they blame on other reasons such as aging.

  38. Several months ago I was told by a good friend and long time Pescatarian that sauteeing with olive oil was a bad call. She told me that when olive oil is heated to high temperatures, that a chemical reaction takes place causing the molecules of the oil to become oxidized and thus creating tiny hooks where they lodge themselves into our blood vessel walls where they can never be extracted! Since then I have used only coconut oil and butter for sauteeing. I am just curious if anyone here at the Apple had read or heard anything like that?

  39. i once read that almost everyone is copper deficient because our soil is very copper deficient from pesticides, etc… that almost all of the once-high-in-copper foods are deficient in copper, as a result. Unless you are eating organic foods, (though they could be lower in copper the first few years of the farm, depending on the prior use of the land).

    That said, i too have had gray hair beginning at age 26 and very noticeable by age 29. But i have stopped dying my hair few times , mainly when i was eating a primarily raw food diet and supplementing with green juice, which, i believe, caused my gray to stop growing in and even start falling out. The new hair coming in was my regular color. It’s not that easy a diet to maintain, but if i drink green juice regularly i notice i have much less gray hair.
    A friend of mine went on Gary Null’s hair program and his hair not only reverted to it’s youthful color but it actually grew back in the spots where it had fallen out! He was 45 at the time. But the hair program is a lot of supplements and a lot of green juice. Like a few quarts a day or more. It’s probably easier to eat raw food and drink some green juice – same results.
    In case anyone is interested, i make my green juice with green apple, celery, kale or collard greens, sometimes cucumber or zucchini or tomato, and lemon juicel Yummy. Lemon juice takes away leafy green bitterness and green apple sweetens it without too much sugar.

  40. I ate like a lot of foods that are like copper iron and stuff like that but it is still not benefits for my grey hair it’s like getting more and more….I’m only 13 I have problem with premature genetics grey hairs man srs if I was u guys who are like 30 years old with grey hairs I don’t even care but if like 13 YEARS OLD MAN THATS REALLY WEIRED LOL…

  41. I have been greying slowly since late twenties
    Tried hair dyes but damaged my very fine hair. I always loved vegetables, any way you can fix them. I always drank very little alcohol. (only socially ) stayed active all my life. I developed Hep-C from a blood transfusion about 40 yrs ago. It couldn’t be fixes until new meds came out late last year. I am free of Hep-C but left with severe liver damage which caused liver cancer. I am being evaluated for liver transplant and have had almost every test you can have for diagnostics. They can’t find anything else wrong with me at this time. I am still active, still feeling good and am caregiver for my grandson who has leukemia. I believe that eating right, not drinking to excess and not doing drugs has gotten me to age 66 in very good shape under adverse conditions. I wouldn’t trade my life for any reason.

  42. Just stumbled across this page and was curious as to how the manipulation of the food- for instance blending food in a blender to dehydrate and make baby snacks that are dissolvable affects the nutritional content- how about adding eggs to bake a puree of veggies??

  43. Graying hair at 28 is 100% normal. You don’t just wake up one day and your hair is all gray.. it happens gradually. I highly doubt it has anything to do with Copper deficiency.