Food Hack: How to Get More Vitamins from Your Produce

Plants are not passive things. Oh, they’re not running and fighting and directly acting on the local environment with any sort of mammalian consciousness or intent, but they do employ defenses against hungry animals, insects, intrusive plant life, and disease – just like we do. We differ greatly in a few major areas, of course. Plants make themselves (or their seeds) unpalatable, indigestible, and downright poisonous through the lectins, gluten, and other antinutrients we enjoy railing against; to defend themselves and their offspring (fuzzy “seeds”), animals bare teeth and claws, run incredibly fast, climb trees, burrow into the ground, or wield semiautomatic rifles. But plants’ and animals’ respective modes of management of “internal” threats, like disease or infection, are more similar than not: we all manufacture antioxidants. With animals, the immune system, which defends from pernicious invading forces and helps determine the inflammatory response to harmful stimuli, is well known by all, but there are also the endogenous antioxidants that animals produce to deal with oxidative stress and free radicals. Humans, for example, have the potent arsenal of glutathione, superoxide dismutase, alpha lipoic acid, catalase, and CoQ10. Vitamin C is another common, endogenous animal antioxidant, just not in bats, guinea pigs, tarsiers, monkeys, humans and other apes.

One funny thing about plant phytochemicals is that they’re not intended for us. They exist to protect the plant. The fact that they seem to be pretty good for us is secondary (but I’ll take it!). Another funny thing about phytochemicals is that they are not static stores. They fluctuate, both up and down. Just as our bodies produce hormones and other endogenous chemicals as they’re needed in the amounts they’re needed, so to do plants increase or decrease levels of phytochemicals in response to stimuli. Take ascorbate, or vitamin C – photosynthetic plants use it for protection from oxidative stress during photosynthesis (using the sun’s energy to create organic compounds, like sugars, out of carbon dioxide, or “cookin’ up some plant food”). More sunlight creates the possibility for more photosynthesis, which creates the need for more ascorbate; more exposure to light, then, results in higher concentrations of ascorbate. This makes sense and is widely accepted by the scientific community. The same general rule applies to other phytochemicals.

Last year, a USDA research plant physiologist by the name of Dr. Gene Lester conducted a fascinating study on the phytochemical metabolism of two types of spinach. He wondered if, since spinach growing in the field relies so heavily on visible sunlight exposure for producing the phytochemicals that make humans want to eat it, perhaps exposing the spinach to light post-harvest continued to affect its phytochemical composition. And so he found out.

Using freshly-harvested, conventionally-grown Texas spinach, Lester’s team measured the various light-sensitive bioactive compounds in the leaves: vitamin C (ascorbate), vitamin K1 (phylloquinone), vitamin B9 (folate), vitamin E (alpha-tocopherol), and the carotenoids (lutein, beta-carotene, zeaxanthin, violaxanthin). The leaves were then packaged into standard clear plastic containers, which were either placed on a shelf with exposure to full retail display lighting or placed in double-thick brown paper bags with zero exposure to light. This went on for nine days. Bioactive compound levels were tested throughout the duration of the study; here’s what changed (or didn’t):

Lester also noted differences between bottom-canopy leaves (older, larger), mid-canopy leaves (younger), and top-canopy leaves (youngest, “baby”). The smaller and younger the leaf, the greater the phytochemical content. Taken together, then, it seems sensible to consider both leaf age/size and exposure to light. If you can’t get freshly harvested spinach, for example, try choosing baby spinach that’s been sitting on top of the pile or stack in the store, exposed to constant supermarket lighting.

I shared a few emails with Dr. Lester, who plainly stated that similar studies would probably be “not necessary” for other green vegetables, since the key variable is photosynthesis. If a plant uses photosynthesis to accumulate bioactive compounds, it’s safe to assume that exposing that plant to continuous light post-harvest will also increase the vitamin and antioxidant content. So – kale, chard, lettuce, broccoli, etc., should all operate under the same principles.

He also speculated that berries should accumulate beneficial compounds and grow richer in color post-harvest when exposed to light, but that it must be UVB as opposed to basic store lighting. I did a bit of digging and found that exposing blueberries to UVC radiation (the type that’s blocked by the ozone and never actually reaches us or our berries) after harvesting had mixed results. It reduced decay and increased or maintained the anthocyanin content, but it wasn’t clear whether the antioxidant effect was due to reduced decay or some other effect of the radiation, or whether it was due to the natural ripening of the berry that would have happened on or off the plant anyway. It’s inconclusive at best.

I did come across a study (PDF) discussing the anthocyanin production of blue corn in response to UVB exposure, in which it’s determined that UVB light, in concert with phytochromes (photoreceptor pigments plants use to detect light), does increase anthocyanin content. This was blue corn still attached to the stalk, not just sitting there after harvest, so it’s impossible to extrapolate it to blueberries sitting in a basket. I guess the question is this: are the phytochromes located on the berry itself and do they remain active after harvest? This study on harvested cranberries, in which light exposure increased anthocyanin content, would indicate that they are and that they do, especially if the same holds true for other berries. Why wouldn’t it?

In light of last week’s sweet potato post, I came across another interesting study on how wounding purple sweet potatoes – literally cutting them with a knife while they were growing – increased antioxidant content, specifically the valuable anthocyanins. They also tried fooling around with light exposure, temperature changes, as well as ethylene and methyl jasmonate treatments, but nothing had any significant effect. Getting in there with a blade did the trick. This makes perfect sense, intuitively; if a plant receives trauma, it’s a good chance something is trying to eat, invade, or infect it. Antioxidants like anthocyanins are there to protect the plant from these exact situations, and so they produce more. And then we eat them anyway. Good deal.

Fascinating stuff, huh? If you take anything away from this at all, it’s that maybe a little corporal punishment is good for your misbehaving plants and that storing berries on the counter or in the sun is probably better than in the fridge (unless your refrigerator light stays on with the door closed). It’s also good to know that we, as consumers of produce, have at least a modicum of agency when it comes to the nutritional density of our food. If we can’t decide what the food producers do to the food while it’s in the ground, and we can’t make it to the farmers’ market for freshly harvested produce from people we trust, and we can’t grow our own food, maybe we can take a few tiny steps to imbue our mass-produced food with more vitamins and phytochemicals. Every little bit helps. And, since self-experimentation is the backbone of this community, put some of these findings into practice and let me know what happens. I don’t expect a full phytochemical composition breakdown, but some subjective experiences are welcome.

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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43 thoughts on “Food Hack: How to Get More Vitamins from Your Produce”

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    1. Great article with very very useful informations. Please, if you visit Tel Aviv 1 day do not hesitate to contact me.

    2. Definitely wow. It really is a great point of view, but some products really need to go to the fridge to maintain their quality and durability.

  1. You’re advocating the STABBING of live sweet potatoes? What kind of message does that send to the children?!?!

    1. These are not teeth belonging to bears; they are teeth that have been bared i.e. uncovered, as in a snarl. Perhaps you remember Mother Hubbard who found her cupboard was bare (without contents).

  2. no wonder why it always feels different when you buy from farmers market or even better if you pick up from your own garden..i can’t forget the taste of wild blueberries at Summerville Lake that grow on the rocks. you need to jump into the lake and climb the rocks from water and reach to blueberries. they are small but never had the same taste in any kind of berries..

  3. I’m not sure what phytochemicals are involved in the colouration although I do know that green is all to do with photosynthesis (of course) but I notice that green leaves kept in the fridge can yellow quite quickly which seems to now make intuitive sense from what Mark’s written about them continuing to photosynthesis when in light after harvest and of course if you leave a tent up for a while the grass is yellow underneath where it hasn’t had the light,doh!

    What I will try is keeping some leaves on the counter and some in the fridge and see if there is a colour difference. I had always assumed it was just the aging of the leaves and that it was preferable to store them cool I’d never made the link with the yellowing grass before!

    You learn something everyday!

    1. GOOD IDEA!!! Im going to try it too! I did throw out a bunch of yellow Kale today that I lost in the fridge! It was a sad day:( I have the new batch on the counter in a vase of fresh water! GREENS ARE GOLD AROUNG HERE!!

  4. I remember reading that mushrooms make Vitamin D if you expose them to sunlight… Kind of like us!

  5. If you look at the Oxygen Radical Absorbing Capacity – which measures the total level of all antioxidants – this increased slowly during storage for all conditions (see Figure 3).

    Light vs darkness didn’t make any difference when you look at this “big picture” number.

  6. OMG!
    I immediately thought of a story I heard many years ago but dismissed as superstitious nonsense. Peasants in San Salvador would severely beat non-producing fruit trees and tell them to shape up. I was told that it always worked. Perhaps the rush of resulting nutrients was responsible for next year’s bumper crop.

  7. Advocating this kind of violence against plant life is exactly why I am a strict carnivore. Shame on you all!

    1. I too thought of a story a woman told me who previously babysat our children. It is much like the San Salvadorian story.

      She had a fruit tree that never bore fruit. One year she gave it a good talking to and threatened it’s very life if it didn’t start producing. Next year it had fruit. Coincidence? Hey, maybe not.

      1. Well… if you play heavy death metal music to a plant, it grows faster (compared to all other forms of music). I actually wouldn’t be too surprised if talking to it like that had some sort of effect… or affect (you decide… dun dun dun!).

  8. Funny part about fooling the potatoe defenses into getting us more of those precious phytochemicals. Right now, all i can say is that fruits and veggies taste oh so much better when bought from a local producer. Especially when it is in Poland, where i come from. Mass-production doesn’t seem to have penetrated deep enough. And although there is not that much sun throughout the year, it always tastes better than whatever you can get in Paris for a decent price.
    I shall take a good look at the links you provided here, Mark.

  9. Makes sense to me. Arguably the spinach (or whatever) is still alive, in the same sense that cut flowers are still alive. They haven’t noticed they’ve been cut, basically.

    So given what it wants (light) and adequate humidity so it doesn’t dry out, it’ll keep on trying to do what it usually does — maximize phytonutrient levels.

  10. To save space in the refrigerator, I have been putting recently cut swiss chard from our garden in a jar with water just like you would with flowers.

    Early in the season they lasted 3 or 4 days or so, without wilting. Later in the season it seemed they wilted in a day or so. Hmmmm.

    Come to think of it, I think I have had pretty good luck with that method with store bought chard. I wonder what makes the difference in the longevity? Amount of sunlight the chard is grown under? Or maybe it’s hydration when it is harvested.

    I never thought it’s nutrients would be increasing as it sat on the table. If true, no doubt a plus.

    1. That’s a neat idea for chard – it would likely work for kale, too, and maybe even leaf lettuce. They all take up a ton of space in the fridge.

  11. Wow, and someone convinced me a while back that the store light deteriorated the vitamins in produce — so I’ve been digging under everything to get the “best” stuff. I am very grateful for this web site.

  12. Pardon, this may be off-topic or misplaced.
    I’d welcome Mark weighing in on this.
    I’ve been reading some of Peter’s stuff at Hyperlipid and gleaning some info that seems to indicate that antioxidants are not all good and free radicals are not all bad. Ingestion of antioxidants may blunt our bodies’ ability to create antioxidants, may blunt exercise muscle-building benefits, and may limit our white blood cells’ ability to hurl free radicals at cancer cells.
    Nothing about biochemistry seems simple or binary.

    1. I was thinking the same thing. Simply maximizing the plant-based anti-oxidants in our diet for its own sake may not be optimal. Like when you take heroin, your body stops production of endorphins, it seems when you flood your body with anti-oxidants from your diet, your body shuts down its own, probably much more effective, anti-oxidant defense. This is something we should be studying more, and why I don’t think that dietary anti-oxidants are such an un-alloyed “win” for our health.

    2. i’ve had friends who’ve kinda become depended on certain supplements… though personally i would still take a few essential ones. how much antioxidants can our bodies produce anyway? surely it can’t hurt to supplement somewhat

  13. Oy.

    Saying this as someone who works in a produce department: If you’re buying at a supermarket, your spinach and greens have been shipped in a cardboard box and kept in a dark cooler in the back of the store until going on display. In order to keep product fresh, any good produce department is going to try to have “just enough” salads on hand to get by and restock through the day. A package of spinach on the top of the stack has seen _maybe_ a couple more hours of light than the package under it; considering that they were both in essentially complete darkness for probably at least a few days beforehand, I would expect the difference in phytochemicals to be negligible.

    As for storing berries on the counter in the sun… well, if you’re going to eat them that day you should be alright. But straws, razzies, and blacks can mold very quickly under those conditions — and what good is a high-phyto berry that you don’t want to eat?

    If you want to play with light exposure and your veg — and I agree that it sounds like a possible way to boost them — it probably makes the most sense to just hardwire your fridge light to “on” or buy fresh veg daily.

  14. This is pretty cool. We try to keep most fruit and some veggies (tomatoes, avocados) on the counter – they ripen nicely and taste better than when stored in the fridge. Berries are tricky in the summer as they go from ripe to fermented an buzzing with fruit flies very rapidly. Maybe we’ll have to put the rest of the produce out on display on our island so that it and we get the vitamin boost!

  15. What an incredible post. It would make sense with out produce to have refrigerator lights on even when they’r closed or see-through refrigerators so our produce has access to either natural/artificial light to keep our produce at an nutritional optimum.

  16. I cut the spinach from its mother, take it inside, cook it an eat it. Hope that’s ok.

    The new seasons strawberries and raspberries might not get much of a counter life either. yum.

  17. What about dried fruit? Should I be taking some dried fruit out of the package and leaving it in light? I would think whatever process is going on here to create more antioxidants needs water though.

    1. Truly actually very good web site article which has got me considering. I never looked at this from your point of view.

  18. This past year I had to cut down my plum tree because it stopped producing fruit the year before. But before I completely chopped it down, I cut about 3 inches deep and left it standing for a few months…due to laziness. To my surprise it started producing a few, albeit very small, plums and it tasted really good. However it was a small batch that I see getting any better. Perhaps I was wrong…

  19. Is it really true that plants don’t provide phytochemicals to some extent for our benefit? Remember animals besides eating plants also provide courier service. In addition in line with the adage “the enemy of my enemy is my friend” particular plants may team up with particular animals against a predator of any kingdom.

  20. A fascinating post.

    I know that lactic acid bacteria (which is the group that most probiotics come from) are not just scattered over the surface of fruits and vegetables but are found in higher numbers at some sites than others.

    In tomatoes, more lactic acid bacteria are at the “scar” site where the stalk was attached to tomato than other areas.

    And this is the piece that many of us cut out to “tidy” up our tomato!

    We’ve still got so much to learn about our plant foods.

  21. My partner and I want to let you know that we loved learning about on this publication, I was just itching to know if you trade featured posts? I am always attempting to find somebody to make deals with but it’s simply a point of view I would inquire.

  22. wow. This is a really interesting and really in deoth post. I would just like to add that eating all of these vegetables organic will provide you with even MORE vitamins and minerals. many people don’t realize that when they buy produce at the grocery store that has been grown with pesticides and other harmful substances, they actually don’t get the entire plants potential for nutrients.

  23. Lots of well-known phytochemicals are available as dietary supplements. However, research suggests that these single supplements are not as beneficial as the foods from which they are derived.
    So it’s really easy and important to include fruits, vegetables, legumes (beans and peas), and grains in your diet.

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