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.
THE Scots national vegetable was the green kale, of which nettles, leeks, onions, ranty-tanty (sorrel), carrots, and turnips were—most of them—probably late and—all of them—certainly inadequate and partial rivals. For unnumbered centuries the place of kale in Scottish domestic economy has been almost as peculiar as that of potatoes during the last two hundred years in the domestic economy of Ireland.
'Although my father was nae laird,
'Tis daffin to be vaunty,
Me keepit aye a gude kale-yaird
A ha' house and a pantry';
and indeed a 'gude kale-yaird' was as indispensable to the old Scottish cotter as the potato-plot is to the Irish peasant. A recent writer on Ireland has bemoaned the adoption by the Irish of ' Raleigh's fatal gift,' which he describes as a 'dangerous tuber' and a 'demoralising esculent.' No dangerous or demoralising tendencies attach to the green kale, nor has it manifested any tendency to 'swell the population,' except in a merely gastric sense. It forestalled the potato to some extent, which in Ireland had become the chief and universal food of the masses before the end of the seventeenth century, but did not come into general use in 'the land o' cakes' and kale till nearly a century later. For a long time the Scottish peasant's treatment of potatoes was curious and tentative. At first his view of them was probably identical with that of the housewife who refused potatoes offered by a neighbour—they would ' eat sae fine with the mutton,' she said—on the ground that' we need nae provocatives in this house.' He regarded them, that is, as less palatable than kale—(which is essentially the vegetable of a carnivorous race, in that it must be used as an adjunct of meat to be at all beneficent)—and less nourishing than oatmeal; and when towards the latter half of the eighteenth century the farmer began planting them in the fields there was a certain apprehension lest it should be attempted to substitute them for the latter. But the potato was bound to win in the end, and in the end the potato won, though the feeling of the Scot for it has never been excessive. He has mastered it, indeed, as completely as the Irishman—who is nothing if not lazy and disposed to rely on every form of energy, from miracles downwards, except his own—has been mastered by it; and he may now be said to have succeeded in making the most that can be made of it, whether as an article of diet or as a source of profit. Its fortune has somewhat modified the position of green kale, but the cotter's garden-plot is still the kale yard, and the time-honoured vegetable, though used less variously than of old, has not been ousted from its place in the nation's esteem. We should explain, however, that it was chiefly among the Lowlanders that kale attained to extraordinary vogue. It is a vegetable essentially Saxon and non-Celtic. The more unsophisticated Highlanders regarded its use as a symptom of effeminacy; so that the Grants who, living near the Lowland line, had grown fond of it were contemned as the 'soft kale-eating Grants.' When the Highlander indulged in such a luxury as broth he preferred the common nettle as more appropriate to the cateran. As for thei aboriginal mountaineer, his appetite for vegetables was chiefly fed on wild fruits and nuts, the roots of wild herbs, and the leaves of certain trees.
In the very early centuries oats and kale were probably far less important staples of diet among the poorer classes than they subsequently became. In the case of Europeans vegetarianism, like teetotalism, is essentially a modern fad, chiefly affected by persons more or less languid and unhealthy both morally and physically. A vigorous and energetic race is always carnivorous, and in later times it was simply the scarcity of flesh that,compelled the Scottish peasant to feed on it so sparingly. The aboriginal cave-dwellers were mighty eaters of meat, and as long as it abounded meat must have formed the chief food of the whole community. Abundant it seems to have been till at least the sixteenth century. Bishop Lesley records of the Bordermen of his time that they made very little use of bread, living chiefly upon flesh, milk and cheese, and sodden barley. The northern Highlanders, who also were marauders, ate flesh largely, and often ate it raw. Lesley, indeed, affirms that they preferred it dripping with blood because it was then 'mair sappie' and nourishing; but his information on the point appears to have been defective, for though they did frequently eat beef and venison raw their custom was to prepare it by squeezing the slices dry between wooden battens. One reason for this ultra-savage style of feeding was probably the original scarcity of cooking utensils, for the Highlander's antipathy to the arts of the craftsman was inveterate. But he was ingenious in a way, and contrived a kitchen-range and buttery of his own. That is, he built a fire, and over that fire he hung the paunch of his last kill, and in that paunch he seethed the flesh of the original owner. According to Lesley, the 'brue ' he got in this way was so excellent that not the best wine nor any other kind of drink might compare to it; and no doubt its quality was very similar to that of the strong Lowland soup called 'skink.' To his habit of battening himself on raw flesh may probably be traced the tradition that now and then he was addicted to cannibalism. (The men of Annandale were also famed for just such dietetic eccentricities.) No doubt the calumny—if calumny it were—obtained a wider and more permanent acceptance by reason of the fact that the authority of St. Jerome could be quoted in support of it. But, calumny or not, it had gained such credence even in Jacobite times in England that when the outlandish host appeared across the Border some nervous folk were seriously concerned lest they or any of theirs should be ravished away to grace some conqueror's board.
As a matter of fact, the ancient Highlander, or at least the Highlander of the later middle ages, was very temperate in food and drink. No doubt he now and then indulged in frantic ' spreeing,' especially after a more than commonly successful foray; but as a rule he despised luxury and eschewed both gluttony and drunkenness. He broke his fast with a light meal, and took nothing more till in the evening he dined in the great hall of his chief. Here the character and quality of the food provided were regulated to some extent by the rank of the guest. But all ate sparingly: corpulence—pace Sir John Falstaff an inconvenient endowment for the professional thief—being held in high abhorrence.
It is quite sad to think now that Scotland is one of the places of the world most affected by bad food. Rates of heart disease, alcoholism, and obesity are unusually high there. People think of soda and shortbread as being "traditional foods." I would say the dietary history of oppression of indigenous customs and adoption of cheap poverty foods as "traditional" is quite similar to what has happened with Native Americans or Pacific Islanders. There may also be some genetic predispositions unique to people who were hunter-gatherers (or mostly hunter-gatherers) until somewhat recently.
Also, it explains how Andrew's potato skepticism may be an ancient cultural trait...
In hunting, the flesh was occasionally eaten raw, after the blood was squeezed out; but the Irish were more accustomed to this barbarous food, and Campion remarks, that the flesh thus swallowed "was boyled in their stomaks with aqua vitae, which they swill in after such a surfeite by quarts and pottles." They also, he says, bled their cattle, and baked the curdled blood spread with butter. A French writer, some centuries ago, describes Scotland as "pauvre en or, et en argent, mais fort bon en vivres;" and again, "assez des veaux et vaches, et par le moyen la chair est a bon compte."