This blog is about the intersection between evolutionary biology and food. But also about practical applications, sustainable agriculture, and general tasty things.
Note: if you do not plan to read the whole post, please skip to the last section
Kale is one of those vegetables that everyone thinks is so healthy. From kale chips to kale salad, kale has become an extremely trendy vegetable. But people have embraced kale without thinking enough about the chemicals it contains and its effects on the Earth. What you don't know could kale you.
Before scientists were blinded by kale’s health food halo, they studied its horrific effect on livestock. Farmers had been mystified by the births of lambs that already had goiter. Researchers experimented with kale on sheep and rabbits with grisly results. Turns out kale does contain a goitrogen, thiocyanate, which is chemically very similar to deadly cyanide. Some young lambs were stillborn, their brain development stunted by their goiters. The consumption of kale had blocked their thyroid’s ability to function properly even in the presence of proper iodine consumption. With many Americans consuming little iodine, especially those obsessed with health foods who eschew iodized salt, the effects could be devastating.
Even more alarming, later experiments showed that mixing the kale with corn and blood meal increased the effect, something you might want to think about next time you consider sauteed kale with cornmeal pancakes and blood sausage.
Scientists then never considered that humans would someday consider kale a “health food.” Back then it was only food for livestock and ignorant Scottish peasants. But even though people weren’t noshing on kale chips all day, kale managed to poison them. Cows grazing on kale transferred its poisons to their milk, affecting the thyroid development of children who drank it and causing an epidemic of goiter on Tasmania.
Kale is also rich in sulfur and compounds that convert to sulfur, which is the chemical that makes rotten eggs smell putrid. One metabolite of sulfur, S-methylcysteine sulphoxide, is known to cause “kale poisoning” – severe hemolytic anemia, a life-threatening breakdown of red blood cells, in livestock. Poor sulfur digestion is associated with many serious illinesses in humans, though whether it causes them or merely exacerbates them remains to be seen.
It makes sense that Kale would be dangerous given it evolved in an evolutionary war against those that dare to eat its leaves from aurochs to insects. One powerful weapon it possesses is lectins, which many of you recognize as a serious danger to human health, implicated in many autoimmune illnesses and other inflammatory disorders. The lectins in kale and other related species are very similar to the equally dangerous wheat germ agglutinin lectin.
Some people think that kale and other related vegetables prevent cancer, but large-scale epidemiological studies have shown no such effect and their phytochemicals may even cause cancer. For example, indole and its derivatives have been shown to promote many types of cancer, possibly by causing hormone imbalances or by stimulating the cyt-P450 pathway that produces genotoxic metabolites. If you already have cancer, it can promote further growth and the so-called “antioxidants” which people think are so healthy can prevent your body from fighting the cancer effectively.
Studies in pigs have shown that kale’s close cousin broccoli promotes severe DNA damage in the colon. Kale may also promote other types of digestive problems through difficult-to-digest carbohydrates known as fructans, part of a family experts are calling FODMAPs (Fermentable, Oligo-, Di-, Mono-saccharides And Polyols). Many people have found relief from IBS and other stomach problems by avoiding foods like kale on a low-FODMAPs diet. If you are constantly bloated and gassy it might be the pound of kale you are eating for breakfast every day.
You probably already worry a lot about antinutrients in grains, but kale contains many of the same antinutrients that rob your body of important vitamins and minerals and irritate the digestive tract including oxalate, phytic acid, and tannins.
The amounts of these chemicals in each variety of kale varies widely, so consuming kale is like eating an uncontrolled cocktail of immunogenic and bioactive health-harming chemicals and their even more chaotic breakdown products. Terrifyingly, these chemicals also vary with time of day and season, even when they are in your fridge!
Kale-ing the Environment
As kale becomes more and more popular, it raises the question: how will we feel the world’s almost 9 billion people on kale? The Food and Agricultural Organization at the UN doesn’t track kale production and consumption yet, but they will have to start. At current rates of growth, by 2350, almost all the world’s cropland will be devoted to kale. The consequences to the environment will be devastating.
Large-scale industrial commercial kale production requires clearing massive amounts of animal habitat and killing animals that invade the fields of kale. In the world of leafy greens production, any life that’s not a leaf is a potential liability. After the spinach-related e.coli outbreak, farmers can’t take the risk of co-existing with other plants and animals. Will the world look like the Salinas Valley looks like today? A sterile dry wasteland where any signs of life are promptly shot or poisoned?
Kale production not only destroys rivers and wetlands, it uses water that human beings need. It needs heavy irrigation during the hot months of the year. Furthermore, kale needs to be fertilized extensively, particularly given its soil-fertility reducing effects, and many farms use industrially-produced resource-intensive fertilizer or fertilizer made from the manure of factory-farmed animals. A full environmental impact analysis of kale production has yet to be done, a fact people ignore when they shovel kale chips blindly into their mouths.
The way kale is grown also increases its negative effects on your health. The EWG lists kale as one of its “dirty dozen” of vegetables most likely to be contaminated by pesticides. Pesticides used on kale include phthalates, dangerous chemicals that are known endocrine disruptors, wreaking havoc on the human hormonal systems. Many pesticides used to grow kale also are contaminated with immune-damaging dioxin and liver-destroying hexachlorobenzene.
Even organic kale might be rife with harm. Laverlam, a common organic pesticide, may trigger allergic reactions, which are on the rise in the United States today. As if kale didn’t destroy enough animal habitat, mineral oil used in organic production destroys the microhabitats founds in soil that are home to a great deal of biodiversity.
Thinking you can beat that by growing kale in your garden? Home-grown greens are known to be heavily contaminated by brain-damaging lead and cancer-causing arsenic.
In the end the best thing you can do for yourself, your family, and the world is to avoid kale and its cousins. This post contains over fifty peer-reviewed references to science, so think about that next time your so-called friend serves you a massaged kale salad with delicious flecks of parmesan reggiano. Remember there is no documented need for kale in your diet and you can get all the nutrients you need from delicious nutritious cow’s liver.
I was going to put this part up the next day, but the reaction I got from the post was so extreme that I almost immediately felt guilty. People sent me emails asking advice about other vegetables that might be bad. Some of the comments were hilarious, some just made me feel bad
And in general people took if very very seriously, I guess they forgot I had put up a poll some time ago asking what food should be my victim to demonstrate you can demonize anything with Pubmed. Also I thought the language was pretty silly: "ignorant Scottish peasants" ... " delicious nutritious cow’s liver"??
Yes, Kale does contain chemicals, all foods do. In very large amounts or in certain vulnerable people could cause problems. Many of the studies I chose involved animals with a diet almost completely based on kale, which I think anyone will agree is a bad idea. Most also involved varieties not sold for human consumption and consumed in ways that humans might not consume- uncooked, un-marinated, etc. A lot of the rest involved just scary language about various chemicals and studies involving isolated chemicals.
I do think that the point about antioxidants being overrated is valid, but overall I don't think kale or most other foods (barring actual intolerances or allergies) are going to cause problems as part of a diverse diet. Maybe you shouldn't juice a pound of kale and drink it for breakfast every day though. Sadly to say, I have met people who do things like that. You have to respect that leaves have to protect themselves from herbivory or these plants would not have survived millions of years of evolution. Some of those chemicals to deter consumption can be healthy in small amounts, but unhealthy in largely amounts.
I will say the issues regarding leafy green production being destructive are worth thinking about, but you can certainly find responsibly-produced kale in season at your local farmer's market. I brought them up because people rarely think about the environmental effects of things that have a moral halo around them like greens, including people more than willing to tell you about how bad meat is for the environment. We should think about the fact that people pretty much demand to have salad greens every single month of the year and what that means for wildlife, wetlands, and biodiversity in general.
But when you see an article that demonizes a food, think about whether or not there are citations and follow those citations. Ask yourself whether they apply to human beings eating a diverse diet with adequete calories. Or whether they involve very high concentrations no human being eats, isolated chemicals, or preparations that no normal human would put on their plate. I see narratives like this, not as satire, in many diet books and on a lot of diet blogs. I have been guilty of this in the past, when I took a lot of stuff seriously that I no longer worry about. Like phytic acid in foods– most of the studies that show this is a problem involve populations of people who are malnourished. I suppose some people get to that point while dieting though.
As far as the cornmeal pancakes with blood sausage and sauteed kale, I think that's what I'm going to have for breakfast today.
A commenter writes in:
I have been wanting to increase my [carbs] and veggies as its pretty much zero right now, I have never felt better(though the current state is less than perfect) but meat is not cheap and I want to have a more diverse diet. But it seems that every time I eat something plant based I start getting acne, rashes, asthma, dry skin and other minor annoyances again, lately I tried to eat potatoes and I immediately noticed a minor shortness of breath and it didn't take more than a couple of days before my face was glowing red and I started getting dry flaking skin. You say you eat rice - brown rice?
Yes, this is a real problem. Many of us started paleo because of sensitivities and diversifying our diets can be frustrating. I don't think this was a problem for humans in the old days, but modern humans have a different immunological milleu. What causes it? A major hypothesis is that it's caused by too-clean environment in childhood, which we can't exactly undo now.
Before I started messing around with my diet and going veg*n and then paleo, I never had acne. But since I went vegetarian I've had it occasionally and while paleo has lessened it, it still appears occasionally, usually alongside scalp issues and keratosis pilaris. Today was one of these days.
My diet before vegetarianism was absolutely atrocious, but I almost never ate vegetables and it was fairly bland. Unfortunately, now that I have discovered the deliciousness of hot peppers, I realize they are the probable cause of my skin issues. I also have problems with many members of the cabbage family.
If you are having a frustrating problem like this, I highly recommend checking out the failsafe diet (the site used to have a more awesome name: Plant Poisons and Other Nasty Stuff). The best strategy is probably to introduce families of plants into your diet gradually until you figure out what is making you sick. The author of that site notes that once she identified some problem foods and avoided them for awhile, she was eventually able to add some back in. Interestingly, she also discovered she had thyroid disease.
For me, it seems the reaction is quite complex. I can eat hot peppers sometimes, but if I eat them in the last week of my menstrual cycle that's when they really wreck my skin.
As far as starches, poatoes are known to be a problem for many people because they are in the nightshade family and contain solanine and some potent glycoalkaloids. Yams are much better tolerated and another rec would be cassava, which is prized for its hypoallergenic qualities. Brown rice is full of stuff that can be a problem, white rice much less so.
Occasionally people will assert that evolutionary nutrition should involve mostly plants. After all, they read somewhere that the !Kung eat most of their calories from plants. And their nutrition science professor said so. Or some vegan book they read. And it's politically correct, so why not?
Here are some facts
I think plant pushers are either trying to be politically correct or relying on outdated info (or sources that rely on outdated info). For example, Boyd Eaton has revised his views on the subject.
Besides, find me a plant food that even rivals the best meat...it's pretty hard. I love vegetables, think they are important, but meat is the core of the paleolithic diet. You can do it with less meat if you want, but don't claim your diet is more authentic or some bullshit.
What did our ancestor's eat? We don't know exactly, but modern hunter-gatherers do not support the notion of a plant-based diet. What does? If you think you have some good evidence let me know, but since it doesn't seem like it makes a difference health-wise, I don't see a reason to advise people to eat mostly plants.
I'm glad I saw this great post about growing your own "salad bowl." A couple of weeks ago I had bought some lettuce seedlings on a whim and put them in a pot on the windowsill. They weren't doing so awesome and I was thinking of throwing them away, but this video gave me hope. A few days later they recovered and tonight I harvested a small salad. It's not a lot, but it was crisp, fresh, and tasty. The plants should keep yielding for awhile if I just pick a few outer leaves each time. Bonsai lettuce...
I also have a few pots of herbs. In Sweden when I needed herbs they sold the actual plants in the produce section, which would last for a week or more if you took care of them. Here they sell them in cut bundles, already wilting and just as expensive. Good thing growing them yourself is easy, but I guess I'm lucky- some city folk don't have a good South facing window like I do.
Bagged salad isn't much better than those wilted herbs. And who knows where it's from or what kind of fertilizer they used? I took my lettuce leaves, a spring of parleys, and poured melted bone marrow, lemon juice, and capers over them. I sprinkled the salad with salt and pepper...it was delicious!
Bergen, Norway dinner with mussels, wolf fish, vegetables, and potatoes...the only thing missing was some lamb or mutton
Louisa asked what carbs I recommend. I did low carb when I started paleo to reduce the excessive amount of bacteria that seemed to cause my IBS. But as I got better I added in more carbohydrates. Personally I enjoy life more with moderate carbohydrate consumption and none of my problems returned. I think low-carb approaches like PaNu are a great approach for losing weight, but I don't think carbohydrates are going to make a slim insulin sensitive individual like me fat. I also think many paleo advocates selectively ignore the large amounts of evidence that roots were important to early humans. I think the best blogs that advocate a sensible approach to carbohydrates for healthy people are Whole Health Source(start with his Kitavan posts) and Primal Wisdom(start with Primal Potatoes).
I do carb cycling. I divide my favorite carbohydrates into rather unscientific categories, trying to rotate them to reduce the odds of me being affected by any antinutrients. My categories are tropical, local winter, and local summer.
The local winter carbs include carrots, squash, potatoes, sweet potatoes, turnips, rutabagas, parsnips, beets, and other vegetables that grow locally. In the winter I often eat a serving or two of these a day.
The local summer carbs include fruits, with a basis towards wild fruits, which I particularly enjoyed in Sweden. When I lived there I would often simply go out into the woods in the morning and gather a basket of lingonberries, sea buckthorn, blueberries, or currants. I think berries can be enjoyed daily in season and more domesticated fruits like apples or apricots with more moderation.
Tropical carbs are more like supplements or treats. They don't grow in New York, but with the Caribbean/SE Asian population in NYC I'd be amiss if I didn't enjoy some plantains, taro, cocoyam, mango, coconut, and other tropical delights similar to what the Kitavans or Okinawans are so healthy eating about once a week or so. Thai coconuts are my favorite because they pack a punch of potassium and it's possible to ferment most of the sugar out of the water.
This is what you will look like if you eat tasty animals
Some of the most common comments on blogs post related to the NYT paleo article seem to contend that we are idiots because meat was a rare treat in the paleolithic and most of the food came from women who gathered tubers and nuts.
Well, I eat tubers and nuts, but these misconceptions seem to be some legacy of politically correct nutrition education. Modern hunter-gatherers do rely heavily on tubers and nuts, but these populations are not representitive of paleolithic populations. The few modern hunter-gatherer populations left live in highly marginal environments are not models of the stone age. Thankfully, we do have isotopic analysis, which allows us to know that paleolithic humans ate meat and plenty of it.
Anthropologist Richard Wrangham is among the few that believe that tubers were very important in our evolution into humans, but most anthropologists consider tubers and nuts inadequate for providing the nutrients that would support the large human brain.
Gathering was important, but it's also important to remember that what anthropologists consider gathering includes foraging for shellfish, insects, and small game. The misconception that women didn't engage in hunting has led to lots of misguided stereotypes of women meekly digging for potatoes while men roamed the plains with spears.
Humans seem to eat tubers when they can, as they are a rich source of calories, but they are not rich in much else. And nuts make little sense as a food we evolved on considering how rich they are in omega-6 fatty acids, which overwhelming cause inflammation in humans.
In a good environment, even a decent hunter could procure some kind of flesh. Big game might have been rare, but there is no evidence that humanity evolved on a plant-based diet. I don't mean to downplay the importance of plants, as I eat plenty of them myself, but seafoods and meat provide nutrients they simply are inefficient in providing.
I hope to post more about this, as well as the other misguided idea that gorilla diets have much to tell us about the optimal human diet (hint: despite the digestive similarities, we don't have large enough colons to make the conversion of fiber into fatty acids a viable food source).
An Italian reporter asked me if I have a "paleo" boyfriend...haha, I don't and actually my boyfriend is pretty adverse to meat and fish, but thankfully part of the way I eat is vegetables and lots of them! I just try to steer boyfriend away from the most processed frankensoy foods and to my delicious pumpkin bisque and crunchy kale.