Dear Mark: Sun Aging Skin, Veggies as Carbs, and What Breaks a Fast

For today’s edition of Dear Mark, I’m answering three questions. First up comes from Carlos, who is worried about the effect of sun exposure on skin aging. Is the type of sun exposure I recommend good for vitamin D levels but bad for the health and appearance of skin? Second, how can someone eat all the vegetables I recommend while keeping their carb intake below acceptable levels? Aren’t veggies really high in carbohydrates? And finally, what “breaks” a fast? How much protein, fat, carbs, and overall calories can a person get away with without shifting completely out of the fasting state?

Let’s go:

Dear Mark,

I read your book about two years ago. Since then I have been following all your advice.

During this period, I lost 33 pounds (5.8 foot, 154 pounds, male) and never had a cold. I am very pleased with the results.

One thing that struck me that you may have pointed out but I don’t recall seeing is your opinion in the matter of sun exposure and skin aging. I do take sunbaths almost everyday, but my girlfriend keeps saying that my skin will get old sooner.

What you think about this?

Thank you in advance.


Everyone’s probably seen this startling image of a lifelong truck driver with unilateral dermatoheliosis. It seems that spending 28 years driving a truck with the same half of your face exposed to window-filtered UVA radiation will prematurely and unilaterally age it.

But this isn’t the type of sun exposure most people get.

Truck drivers are notoriously sleep-deprived, averaging under 5 hours of sleep per day according to one experimental study. Not only that, but what little sleep they do get is all over the place. They’re napping, they’re sleeping in their rig, they’re sleeping at odd times of the day — whenever and wherever they can get away with it. In short, their circadian rhythms are likely disordered, and a disordered circadian rhythm impairs your skin’s ability to recover from sun exposure.

And truck drivers are not getting full-spectrum UV, as car windows do not allow UVB through, only UVA. UVA penetrates deep into the epidermis, which causes aging. UVB interacts mostly with the top layers of skin and is the wavelength response for vitamin D synthesis. Just like the right amount of sun exposure can actually protect against melanoma via vitamin D production, it’s also likely to protect against premature skin aging, as vitamin D directly protects against skin aging. The trucker wasn’t making any vitamin D, so he had nothing to counter the photo-aging effect of the UVA. If you’re getting moderate doses of midday sun (high UVB:UVA ratio), you’ll make adequate vitamin D.

Take a guy like Laird Hamilton, who famously eschews sunscreen and, as a big wave surfer, stand up paddler, and all around waterman, gets a good amount of full-spectrum sun. Take a look yourself. He’s 51. Does he look it? I run into Laird from time to time in Malibu, and I can verify that he looks great for his age.

Now, look: don’t be the overweight British expat with the tanned red leather hide who spends his days sunning, eating tapas, and guzzling cervezas in southern Spain. That’s not what I’m promoting. Be sensible, avoid burning (and prolonged exposure through glass), and you should be okay.


I eat paleo but can’t shift belly fat. I am really struggling to keep my carbs under 150. I track on fit day and basically eat the same things each day. The carbs I eat are 1 small banana, 1 tinned veg soup, 1 cup cooked veg and 1 cup salad, 1 cup almond milk and a Cliff bar. I eat my fats and proteins on top of that. I am seriously wondering if Fitday is doing the maths wrong as it seems like so little veg and fruit to me. I get HUNGRY. When I read other posts it seems like people are eating mountains of veggies. How can that be when 1 cup cooked veg is 23 grams of carbs and salad 2 grams. I am so confused!! Please advise 🙂


I hear you, Sasha. It can be confusing. I’ve tried to set the record straight on this topic, but it hasn’t gotten through to everyone. So I’ll do it again.

I find it easier (and more helpful) to think of non-starchy vegetables as “free” than to bother subtracting fiber from carbohydrates or counting them as total carbs. Leafy greens? Spinach? Kale? Asparagus? Broccoli? Bok choy? Summer squash? Zucchini? Cabbage? Eat as much as you want. The carbohydrates are negligible (you probably use more glucose digesting non-starchy vegetables than they contain) and they’re inherently self-limiting. No one is carbing up with a salad bowl full of a couple pounds of steamed kale before a race. It simply wouldn’t work and you wouldn’t be able to eat (or digest) it all in a single sitting. No one is carb-binging on spinach the way they might binge on roasted potatoes; spinach technically has carbs, but not many. No one is getting fat because they ate too much lettuce unless it’s drowning in dressing. We are not gorillas with enormous fermentation chambers sitting in our bellies. We benefit from fibrous veggies but not because they provide ample energy to us.

The carbs on the Primal Blueprint Carb Curve primarily refer to carbohydrates from starchy vegetables (winter squash, beets, etc), tubers, roots, and fruit, so only count those against your carb intake. Oh, and any sweeteners (like honey), too.

Let’s look at your daily “carb” intake.

Small banana — about 20 grams of carbs

Cliff bar — about 20-25 carbs

1 cup almond milk — 7 grams of carbs

1 cup salad — negligible

1 can of vegetable soup — 18 grams of carbs (but may be significantly less depending on the brand; if it contains carrots, potatoes, and other root vegetables, it will be on the high side)

1 cup cooked vegetables — negligible, assuming these are green fibrous leafy vegetables

Best case scenario, you’re eating maybe 60 grams of actual, digestible, bioavailable carbs, and that’s if we count the vegetable soup. I suspect you’re eating considerably fewer than that.

As for the belly fat, it is often the last to go for people, especially those who’ve burned off most of their excess body fat and are sitting at or near their goal weight. You may want to try eating a few more (starchy) carbs as you approach your goal weight. That seems to help some people.

Also, be sure to sign up for the newsletter so you can get access to my fat loss troubleshooting guide. It was just released, it’s free to subscribers, and it’s meant for people just like you — those who are trying to lose the last bit of stubborn fat.

Hi Mark,

A couple of weeks ago you answered another reader’s question and now I’m a little confused. In your answer (I don’t remember the question specifically) you suggested that perhaps he/she was not eating enough to break their fast.

That’s where you got me. I thought fasting = NOT eating. Therefore, breaking said fast = eating.

I would love some clarification on this. Is it a calorie thing? Fat content? Protein?

Could I have my morning coffee with cream (around 80 cal.) but nothing else and still be fasting? Could I eat veggies but not fruit? Does an egg break a fast?

This enquiring mind wants to know!

Thanks for sharing any info. you have on this.


Great question. Let me explain.

As I see it, fasting is more of a spectrum than an on-off switch. The biggest determinant is insulin: elevations in insulin inhibit or “turn off” the activity of AMPK, the “fasting” enzyme responsible for many of the health benefits.

Enough protein breaks a fast. Protein, especially protein containing the amino acids lysine, leucine, isoleucine, and valine spikes insulin and turns off AMPK.

Enough carbs break a fast. Carbs are highly insulinogenic.

Fat is the least likely to de-activate AMPK, but if you eat enough (anything more than a moderate dollop of cream in your coffee) you can blunt endogenous fat burning. Beware of studies discussing “high-fat diets” and AMPK, as their idea of a high-fat diet is high in both (refined, trans) fats and sugar. Laboratory high-fat diets are simply diets designed to reliably induce obesity in rodents; they are not analogous to healthy high-fat diets.

I’d venture to guess coffee with a little cream will preserve AMPK activity (though burning off incoming fat will slow burning off fat reserves). A small meal of fibrous vegetables won’t really qualify as a proper meal and shouldn’t impair the fasting response much. An egg, which is high in quality protein, probably will “break” the fast. Same for sugary fruit, whose carbs are easily absorbed.

But ultimately, it depends on how your unique body chemistry responds to the food. The more insulin sensitive you are, the more food (protein, carbs, overall calories) you’ll be able to handle without spiking insulin and thereby breaking the fast.

The woman from the Dear Mark question was trying to break a fast with a single orange or grapefruit. These are small fruits with relatively low levels of sugar, particularly the grapefruit. It’s just not a lot of food. So if you’re trying to eat something without ruining the fast, one of those fruits may work. But heed the issues raised in that post; she wasn’t breaking the fast with enough food and really suffered for it.

That’s it for this week, folks. Be sure to write in with your advice for today’s stable of questions. How do you break a fast? How do you not while still eating? Has your sun intake aged you? Do you count the carbs in vegetables? Thanks for reading!

TAGS:  dear mark

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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36 thoughts on “Dear Mark: Sun Aging Skin, Veggies as Carbs, and What Breaks a Fast”

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  1. Regarding this truck driver–I can’t help but wonder if he sleeps on that side as well. The wrinkle pattern makes me think he does. Mushing your face down on one side constantly can make a big difference, and as Mark alluded to, he’s probably not getting enough quality sleep to repair from sun damage (and face-mushing). Someone needs to tell him to flip over once in a while.

  2. I don’t know, it seems like we’re still missing some real science here on sun exposure/aging/primal diet. One (possibly sleep deprived) wrinkled trucker and one hot surfer aren’t convincing me.

    I’ll add my own anecdotal evidence: I’ve always burned easily and so I never sunbathed like my friends and sisters. Then in my late 20s I started obsessively wearing sunscreen on my face, rain or shine, all year round. I’m 37 now and see a MAJOR difference between friends/sisters and me. I have almost no wrinkles.

    I haven’t gone all-out primal until the last year or so, so that’s not the reason. Maybe now a primal diet would make the sunscreen less necessary and give me the same wrinkle-free skin? (I still burn as often as I did before, so not sure about that.) Either way, I’m vain so I’m not chancing it!

    1. I used to walk several miles home from a job I had and the sun would be on my right, 3 – 5 days a week for around 2 years. I’ve always worn moisturisers with sun screen so my face isn’t noticeably different, but the back of my (formerly unprotected) right hand does look older than the left now. And I’d notice at the time it was markedly more tanned.

      That was years ago but now the skin on my hand that one side is thinner and less plump, and unlike the rest of me, looks my real age.

      Make of this what you will, maybe necks, faces, cleavage (and backs of hands!) which are known to show age need protecting (for those of us willing to sacrifice a little for vality), whereas arms and shoulders, and legs, less so?

    2. Wrinkle-free skin can be hereditary. I’ve rarely used sunscreen because I don’t like having all those toxic chemicals on my skin, but I don’t have wrinkles. My mother never used sunscreen and didn’t have wrinkles either. It depends more on the type of skin you’re born with. Your sisters might not have been as fortunate.

      1. I too believe it’s up to genetics and dumb luck.

        Have you tried mineral sunscreens? The good ones don’t have a bunch of toxic chemicals.

        1. Mineral sunscreens contain zinc oxide and titanium dioxide as active ingredients. They don’t protect from UVA rays very well, and the UVA rays are the ones tha age skin. Sadly, it’s exactly those “toxic chemicals” that are best for anti-aging.

      2. Sure, I guess it’s possible that, although we have near identical genetic makeup, my wrinkle-free skin is completely unrelated to my diligent use of sunscreen, and my sisters’ wrinkles are completely unrelated to their histories of tanning. But it’s not like we have zero evidence that UVA rays contribute to premature aging. There’s plenty out there! Does a paleo diet make things more complex? Who knows, but I haven’t seen enough evidence to prove that’s true. I’m sticking with the evidence we do have and my own experience.

        1. To Sunjammer:

          Just based on my personal experience, since I started using mineral sunscreen (vs chemical sunscreen) two years ago, my skin looks about 1000 times better, and my obvious and embarrassing melasma has diminished.

          To reiterate: I have used chemical sunscreen for years, but it’s only since I started using mineral sunscreen that my skin started looking younger and less sun-damaged. I guess this is one of those instances of Mark’s “n = 1” as proof of what works for me.

          I realize that no product is perfect, but given the results I’ve experienced, I am completely comfortable recommending mineral sunscreen to my friends. (Only because they routinely ask how it is that I look so young — I don’t go around telling people what they should do with their beauty routines.)

  3. For the first time in my life, since starting the primal lifestyle, I had a weekend day of sun exposure that had me convinced I ‘over did it’. Within a few days, skin was nice and tan and I DID NOT PEEL. First time ever. It may seem insignificant, but it sure seemed to fall in line with the benefits/science that Mark has explained.

  4. “Fat is the least likely to de-activate AMPK, but if you eat enough (anything more than a moderate dollop of cream in your coffee) you can blunt endogenous fat burning. ”

    How big is a dollop? Specifically, I am wondering whether a teaspoon of cod liver oil in the morning will break a fast that would otherwise persist until noon with lunch.


  5. The only Primal approved Cliff bar is using the edge of a cliff as a pullup bar.

  6. With regard to losing belly fat, I started on intermittent fasting three months before I started paleo eating. Over a year and a half I lost a total of 90 pounds. The belly fat came off as evenly as the rest. I suspect the intermittent fasting had something to do with that. I started out within 8 hour eating window and gradually narrow that so that normally I eat all my calories in a four to six hour window.

  7. I guestimated 20-25 carbs for a cliff bar this weekend. As I was finishing it I checked the label and was stunned to see that it actually listed 41 grams of total carbs! (No wonder I was hungry an hour later.)

    I’m not venturing into cliff territory anymore.

  8. Wonderfully clear explanations on the “carbs from veggies” and “breaking fast” questions–will be really helpful to share this post with clients. Thank you!

  9. Now I’m confused!

    Regarding the recording of carbs, if I’m counting total daily calorie intake and at the same time aiming to consume 30% of those calories from carbs, how should the green vegetables be taken into account? Should I include them in the calorie total but not the carbs, or do I simply not record them at all for either??

    Also……regarding the paper on the insulinogenic effect of whey protein, does this suggest that by using whey powder to supplement your protein intake, you’re actually causing the same unhealthy insulin spikes that you would get from eating things like white bread and other high GI foods that you should be trying to avoid?

    1. I consider all vegetables free. Both in calories and carbs. Even squashes. My personal experience is vegetables don’t count. In fact, the more vegetables I eat, the leaner I get. This is probably a combination of the veggies displacing other food choices, the fiber content, and the energy required to digest them versus the energy they provide.

      I take whey protein everyday. I certainly wouldn’t stop over the possible effects on insulin unless you are diabetic. Protein is awesome and the whole insulin thing, for people who don’t have insulin resistance issues, is way overblown. Insulin is not poison and is actually anabolic and an important part of muscular development.

  10. Not everyone can follow your recommended vegetables. Everyone is a unique individual and must find out for themselves what they can safely eat. It’s been a long road of searching for me. I’m 69 years old and very insulin resistant. I have tested many foods after consumption for spiking my blood sugar, summer squash and zucchini and cabbage all raise my blood sugar. Pumpkin does not, but I do not like pumpkin. Genetic mutations have a serious effect on my methylation cycle. Broccoli and kale make my leg muscles ache.

  11. I’ve been making sure to always break my fast with a high-protein meal, at least 30 grams. But I see you talking about breaking it with fruit only- do you think high protein for the first meal of the day is unnecessary, as long as you get your daily protein requirement at some point?

  12. If Sasha says she is so HUNGRY, I say she needs more fat. If I eat enough fat I do not get hungry. I don’t consider a cliff bar to be primal. Maybe on occasion one if your in a pinch but otherwise isn’t a lot of this lifestyle about staying close to how our ancestors ate? Eating whole unprocessed foods is my first goal and then tweaking the macronutrients. Years ago on a physician supervised diet (high protein for its time) they told me never eat more than a half a banana a day or you won’t lose weight. I’m not sure if it’s true but it has stuck in my head and actually I think a whole banana is too high a glucose load for me personally. Maybe cut the banana in half and add some nut butter to help you feel satisfied. Good luck and focus on how you feel and not the numbers on the scale.

  13. So, Mark, as far as Bulletproof coffee, which I add 1 tbsp of grassfed butter and 2 tbsp of MCT oil – is that inclusive of keeping my fast going or would that many calories (300 or so) either break it, cause an insulin response from the butter or undermine my fat burning efforts altogether?

  14. I’ve been wondering if a tablespoon of collagen in black coffee is enough to “break the fast.” I’ve been doing some intermittent fasting and will not have my first meal until 12 or 1:00, but I have black coffee, often with collagen dissolved in it. I really don’t know whether that is still considered intermittent fasting or not, then. Any thoughts would be appreciated. Thanks!

  15. To bust the belly fat – you need to be doing sprints once a week, and the body/ weight training, especially heavy leg work. Ironically, restricting carbs too much will prevent you from doing intense workouts to your full potential, and you’ll stall your fat burning efforts. I also found as the belly fat gets lower and lower, the body resists more and more to shed it – you just have to stay consistent – starving yourself of carbs in hopes to get rid of the belly fat will actually prompt your body to try and store it, and will sap your energy when you try to do a hard workout.

      1. extra info: The best time to eat some starchy is carbs is right after a hard workout – as long as the glucose stores in the muscles are depleted (so, a casual walk won’t cut it), the glucose hitting the bloodstream will be directly be taken up by the muscles, with no insulin needed to trigger the uptake. If, after you deplete you glycogen stores, you insist on going low carb, the brain will freak due to lack of glucose, and it will trigger a cortisol response, immediately sacrificing lean muscle mass into glucose to power the brain which is your bodies first priority, and the high cortisol levels will of course immediately halt all fat burning, and you will go into emergency “fat storing mode”. Low carb is for non-training days. This is why highly active people suffer much less of an insulin problem, and can “get away” with eating starchy carbs versus people who don’t exercise HIT. The more muscles you hit in your workout the better – and the more fast carbs you will need to recover. Avoid the “cortisol emergency” response, and you’ll burn fat for days after a workout. This is also the reason why if you don’t do intense exercise sessions, you can go as low carb as you want, but you will still fail eventually – every little bit of extra glucose will cause an insulin response, not to mention you’ll have low muscle mass, and be sick and weakly.

  16. With regard to the veggies/carbs question: the letter-writer seems to be mostly eating very highly digestible concentrated carbohydrates: the banana, tinned veggie soup, and Cliff bar. These are rapidly processed and will cause rapid insulin spikes, followed by crashes and constant feelings of hunger. These rapidly processed carbs also tend to be rapidly shifted into fat stores, to lower blood sugar. This could explain the lingering belly fat.

    1. I thought the same, I typed a reply but then I do worry about being too fanatical… but yes I agree fwiw.

      A diet like that would have me starved and gaining weight within a few weeks.

      They’re also very dense foods, home-made veg soup is bulkier.

      1. I agree! Everything Sasha eats, except the salad, is dense. I wonder what the cooked vegetable is, as 1 cup of cooked broccoli contains only 11.2 grams of carbohydrate.

        Another thing to take into account: women and men metabolize carbohydrates differently. I remember reading some studies that showed that men (usually) burn dietary carbohydrate for energy, and store dietary fat as fat, while women (usually) do the reverse. I’ll have to hunt them up again!

  17. That 50-year-old surfer has older-looking skin than most 50-year-old Buffalonians living in New York. My boyfriend is from Buffalo. He said when he moved to California he was so confused. He couldn’t tell how old people were. Everywhere he looked were young people with old faces. He said in New York you tell how old someone is by how fat they are. In California hardly anyone was fat, but their faces looked old. My own 50-year-old face looks way too old to be only 50. I suppose I can thank being a Swedish-Finn growing up in Southern California and never wearing sunblock. I wish there was a way to fix it.

    1. Research skin products with urea in (you may need to look up the names it’s called on labels) – this plumps your skin temporarily, and if you use it regularly over time will help diminish wrinkles. Also research using chicken fat, goose or duck fat, and even lard as a skin treatment in place of olive or coconut oils.

      I have an older friend who swears by lard (obviously get the purest you can) and although it sounds strange it’s made a difference on my own skin as well!

      My name on this post links to a blog post I found about it. Just ideas but these two replace the fluid and fats that sun-damaged skin struggles with. Good luck. 🙂

  18. Regarding the trucker….He may have also smoked. I remember seeing a picture of my dad and his 4-6 year younger brother. My dad quit smoking at about 32 and his brother smoked all of his life. In the picture my uncle looked older than my dad.

  19. Laird Hamilton certainly looks his age. And if he didn’t have that glorious blond hair, he’d look even older. If I know I’ll be in direct sun for more than 10-15 minutes, I use sunscreen on my face and hands to minimize the wrinkles. And it works, because I’m 45 and still get carded!

    1. I agree. Laird looks amazing. Thick blonde hair and a fit body. However, just judging by his face, he most definitely looks his age, maybe even older. It’s the fit illusion. All my surf buddies have it. Being really fit and exposing yourself to the elements gives you this vigor and glow. It really does. And that glow overwhelms others perceptions of your age because the viewer is receiving a lot of cues that indicate youth (narrow waist, muscles, good postured, confidence, etc). Mark’s a really good example of that. If you just counted the wrinkles on his face, you would guess his age correctly or perhaps over estimate. However, taken as a whole, your perception is youth.

      I surf with a guy like that. His face says 70’s, but his body says 40’s. It’s really weird. Like someone photoshopped his head on another body. But when you see him from a distance, you’d underestimate his age by a good 20 years because his overt health signals indicate youth.

    2. Sure, if that sort of thing is important to you but Hamilton hardly looks “his age.” I mean, to me, he has the face of a guy who’s done a lot of, a lot of it. His face doesn’t look “old” at all. Certainly he’s fit but what does 51 look like, anyhow? If the trade off is between living harmoniously as possibly between the modern world and nature itself and preserving one’s youthful looks with constant prep and diligence, then I’ll be happy with “looking my facial age” and being fit in the effortless and easy way that Hamilton looks. Don’t forget about the years (decades) of Omega6 and cortisol damage that Mark had committed to his body and yet, he still looks vital. What one does in their early years as far as poor diet, drugs, alcohol, over training or whatever abuse one can think of, has a huge bearing on how they will look and feel later, I believe. Sooner or later, you’ll realize that no one cards you anymore but as you age, perhaps then you’ll realize that maybe soaking up the all important vitamin D in your younger years was probably the better bet.

  20. Sun exposure. It’s a tricky one for Australians, because the hole in the Ozone covers the country, and the last I heard, Australians have the highest rate of skin cancer in the world. In now live in Europe, have low Vit D levels (taking supplements) and an underactive thyroid, which seems to be an issue for this area – and so I try to get as much daily sun as possible. But if I was still in Australia, I doubt that I’d be so keen. Sun hats for Australian kids are obligatory, and long sleeves for beach ware. So I think country counts.

    Carbs. Love the “We are not gorillas” sentence!

    Fasting? I’m hungry all the time – yes, the fat intake helps. Half a can of coconut milk (preferably in the form of gelato) feels good, keeps me satisfied for longer. I basically feel like I’m fasting every time I manage to not eat between meals!

  21. Sounds like Sasha is a vegetarian?? Maybe it will be too hard for a vegetarian to slim down and burn off that last piece of stubborn fats? ????