Why people who hate their veggies may have a superpower.
There are many and complicated reasons why some people don’t like veggies, as BILL SULLIVAN explains in this extract from his new book.
“I DO NOT LIKE BROCCOLI. And I haven’t liked it since I was a little kid and my mother made me eat it. And I’m President of the United States and I’m not going to eat any more broccoli.” – George H. W. Bush.
There is no question that broccoli is good for you – but for me and about 25 percent of the population, it tastes like dog’s breath. Ditto for kale, brussels sprouts, cauliflower, and most of the other cruciferous vegetables parents mercilessly force upon our protesting taste buds. My aversion to these popular veggies has made me the object of ridicule at many social dinners. There are so many fascinating topics that we could talk about, but the conversation inevitably turns into another annoying inquisition probing my dietary habits.
“You don’t even like salad?!” No. If a plate of salad is in front of me, I react just as Ron Swanson did on Parks and Recreation: “There’s been a mistake. You’ve accidentally given me the food that my food eats.”
“It’s probably a psychological trauma. Did your mom shove broccoli down your throat as a child?” No. I would stuff the entire portion into my mouth and claim that I had to use the bathroom.
“You’re a scientist, surely you realise how nutritious vegetables are?” Yes, but for this scientist at least, it’s not easy eating greens. I’ll take the carrots instead.
Sometimes I feel like I need to have surgery to remove these people from my back, but when I’m the one getting grilled at a cookout, I can’t help but wonder what is wrong with me. I see someone shovel in a mouthful of some green vegetable – deliberately – and then genuinely enjoy it. I am green with envy.
Certain vegetables aren’t the only item on the menu that might cause contention among diners. Some people have a major sweet tooth. Some love spicy foods. Some can’t handle dairy products. Some can’t function without their coffee. Some don’t like to drink alcohol, and others are very finicky about their wine. And some people like to eat bizarre items that many would not consider edible. Everyone’s tongue looks the same, so why do our tastes in food and beverage vary so much? Is there hope of achieving peace at the dinner table?
WHY YOU HATE BROCCOLI
Our varying fondness for broccoli was famously played out in the “Chicken Roaster” episode of Seinfeld. Kramer is protesting the Kenny Rogers Roasters restaurant, but becomes addicted to their food after trying it. He then devises a covert operation to have his buddy Newman buy meals from the restaurant for him. Jerry gets suspicious when Newman is caught buying broccoli at the restaurant, because Newman “wouldn’t eat broccoli if it was deep-fried in chocolate sauce”. To dispel Jerry’s suspicions, Newman claims to love broccoli. But when Jerry challenges Newman to eat a piece, he quickly spits it out, calls it a “vile weed,” and does a honey mustard shot to dampen the bitter taste.
Newman is clearly a “supertaster”, a term physiological psychologist Linda Bartoshuk coined to describe people like me who have a heightened sense of taste. To be a supertaster might sound like a good thing, but it’s not. Instead of an “S” on my chest, it’s more like a scarlet letter on my forehead.
Do you think you might be a supertaster, too? Well, you can test yourself. A bit of blue food colouring on your tongue will stain everything except the taste buds, which will appear as pinkish bumps. Stick one of those loose-leaf paper reinforcement circles onto the tip of your tongue and tally up the taste buds in the circle using a magnifying glass. Supertasters tend to have more taste buds, usually 30 or more, within that circle.
Each taste bud is made up of about 50 to 150 taste receptor cells. A gene family called TAS2R (appropriately pronounced as “taster”) makes the taste receptors on these cells that bind to molecules in our food or drink. After these molecules get into our mouth and bind to our taste receptors, the signal is relayed to our brain. Ahhhhhh, Reese’s Peanut Butter Cups . . .or, Oh crap, kale!
In addition to having more taste buds, supertasters can also have genetic variations in their TAS2R genes that make their taste receptors better at detecting bitter flavours. A TAS2R gene called TAS2R38 registers thiourea compounds present in many vegetables.
Hard to imagine that even a vegetarian’s diet contains something as sinister sounding as thiourea, but this is just one of the many chemicals that make up broccoli. This is why scientists recoil at the selfproclaimed “Food Babe” Vani Deva Hari, who once warned, “There is just no acceptable level of any chemical to ingest, ever.” All of our food is made of chemicals, even if it is organic and non-GMO.
In the 1930s, Arthur Fox, a DuPont chemist, was the first to note the different reactions people have to thiourea compounds. Fox accidentally splashed some of these chemicals onto himself and a lab mate; the chemicals didn’t bother Fox, but his fellow chemist complained about their bitter taste. Fox was not a supertaster. His lab mate was. This was some of the first direct evidence that what one person tastes is not necessarily the same as what another person does.
The variations in TAS2R38 among people are due to differences in their DNA sequence at this gene, which essentially means the taste bud protein produced by that gene is going to be different. Specifically, the DNA of supertasters builds taste receptors that register thiourea compounds as incredibly bitter. A supertaster’s brain assumes that the green horror he just stuck in his mouth must be unfit for human
consumption. Now, broccoli won’t actually make supertasters physically ill. But the bitterness is so potent that it can sometimes trigger their gag reflex. Said another way, the TAS2R38 variation in supertasters is DNA’s attempt to play it safe and protect them from potentially poisonous plants.
It is important to remind ourselves that we are products of our DNA, the molecule that is singlemindedly dedicated to the mission of copying itself. DNA builds living creatures like us to serve as its survival machine and to maximise its chances of getting passed into another generation. (Sounds cold, but we’re keeping it real here.)
As survival machines, we are equipped with taste buds to help us discriminate what might be useful to our bodies from what might be lethal. To understand our tastes, we need to recognise that plants are survival machines too. Because plants can’t flee predators, their DNA has developed alternative protection strategies. One tactic is to make their parts unpalatable or downright toxic so that animals will stop munching on them. By producing bitter-tasting chemicals, plants can deter broccoli haters like me from making them lunch.
One strategy plants use for reproduction takes advantage of animals that have a sweet tooth. Such plants surround their seeds in a sugary fruit so animals will eat them and unwittingly spread the plant’s seeds around. Plants are very manipulative when you think about it. If I could eat salad, I would eat it angrily, stabbing my fork through those hearts of romaine with gusto.
WHY YOU LOVE BROCCOLI
If TAS2R38 variations protect us from eating poisonous plants, why don’t we all hate broccoli? It most likely depends on the types of plants that were present in the environment of our distant ancestors.
If our ancestors evolved in an area filled with poisonous plants, having the supertaster gene could have conferred a survival advantage. On the other hand, this blessing could become a curse if those plants are indeed edible; in this case, the supertasters cannot reap the nutritional benefits, because their taste buds have misled them.
Many other genes besides taste bud receptors influence what flavours we find palatable and how we metabolise (or break down) certain foods. Finding and characterising these genes is a new science called nutrigenetics.
In a 2016 study, geneticist Paolo Gasparini at the University of Trieste in Italy uncovered 15 new genes linked to people’s preferences for various foods – from artichokes to yogurt. He identified these new genes by combing through the genome sequences of more than 4500 individuals to find genes linked to 20 different foods these people liked. Interestingly, none of these genes are the usual suspects of smell and taste receptors, meaning we still have a lot to learn about why our bodies give a thumbs-down to certain foods.
WHY YOU CAN’T SAY NO TO SUGAR
Not much can happen during your day that a little chocolate can’t fix. But, believe it or not, not all mammals share a love for sweets. Did you ever try to break off a piece of that Kit Kat bar for your feline friend? Wonder why your gracious act was met with icy indifference? Strict carnivores like cats don’t have the taste receptors to detect sweetness. (Surely this explains Grumpy Cat?)
In our modern world, our taste receptors for sweetness actually get us into dietary trouble. In the old days, our primate ancestors relied on ripened fruits to supply their bodies with caloric energy. Because fruits contain the most sugar when ripe, we evolved a sweet tooth to make sure we get the best bang for our buck when extracting energy from food.
Therefore, our love of sweets is deeply rooted into our evolutionary heritage and is a very hard habit to break. However, you may have noticed that some people will easily surrender a doughnut, while others will fight to the death for it.
A gene variant for a sweet tooth has indeed been found – and not everyone has it. These mutants walk among us, turning down desserts and making the rest of us feel guilty. (I’m pretty sure my wife has the sweet tooth gene, though. When I ask her to split a cupcake with me, she gives me the bottom half.)
A 2008 study carried out by nutritional scientist Ahmed El-Sohemy at the University of Toronto identified a variant in a gene called SLCa2, which correlates with a tendency to take two lumps of sugar instead of one. SLCa2 encodes for a protein called GLUT2, which brings glucose sugar from our blood into our brain cells where it is broken down for energy. Researchers believe that this change in the GLUT2 receptor interferes with glucose sensing, and as a result, the body doesn’t have a reliable measure of how much glucose is in the blood. You could have a full tank, but your glucose gauge says you are only half full. So you have a second piece of cake, blissfully unaware that you’re already sweetened. Studies in mice support this idea: Mice bred to lack GLUT2 will keep on eating even after their brain is marinated in glucose. In people, SLCa2 gene variants correlate with an increased risk for type 2 diabetes.
WHY YOU LOVE JUNK FOOD
Do you still think that turning down junk food is strictly a matter of will? What if I told you that a predilection for junk food could have been programmed into your DNA before you were even born? As it turns out, mothers who eat a “junk food” diet rich in sugar, salt, and fat give birth to children who have a seemingly inborn desire for junk food as well. In humans, we think this is because the kids grow up in a household that eats poorly. No one would dispute that possibility, but experiments on lab rats suggest more might be going on than first meets the eye.
Chew on this: A 2007 study showed that rat pups born to mothers fed a junk food diet during pregnancy developed an increased preference for fatty, sugary, and salty foods. Rat pups born to mothers who ate a healthy diet during pregnancy did not want the junk food.
How might this happen? Because it is highly unlikely that the foetus accrued gene mutations because of a mother’s junk food diet while in the womb, scientists suspect foetal programming took place:
The mother’s diet alters the DNA of the unborn child at the epigenetic level. In other words, the junk food did not change gene sequences; rather, it changed the expression levels of certain genes. It would be like the time Fergie sang the National Anthem at the 2018 NBA All-Star Game; the lyrics were the same, but the song was very different.
So although it is not surprising that kids who grow up regularly consuming junk food are likely to become junk food junkies, numerous studies suggest that a proclivity toward junk food could have been programmed into the fabric of their DNA before the cord was cut.
One major way DNA can be epigenetically programmed is through methylation, a chemical modification to the DNA that affects a gene’s expression. The more a gene is methylated, the less it is expressed. If you think of gene expression as a highway, DNA methylation marks would be like a bunch of orange traffic cones strewn across that highway, slowing things down.
A 2014 study took a look at the level of DNA methylation taking place at a gene called proopiomelanocortin (POMC) in the pups born to rats that were on junk food diets during pregnancy. The POMC gene gives rise to a key hormone that decreases appetite. Rat mothers who consumed a high-fat diet gave birth to pups that had higher levels of methylation at their POMC gene, which means that less of this appetite-suppressing hormone is made in these pups. So mothers gorging on junk food gave birth to offspring that were programmed in utero to be born hungrier than offspring whose mothers ate right.
What happens if the pups of junk food mothers were forced to eat a healthy diet? Is it possible to reverse the DNA programming that occurred in the womb? Unfortunately, this does not appear to be the case, at least in the aforementioned 2014 study: a healthy diet did not return DNA methylation levels at POMC to normal.
In other words, the mother’s junk food diet had permanent effects on a baby’s DNA. If true in people, this might explain why it is so hard for some to control what or how much they eat. There may be a critical window during foetal development when DNA methylation is laid down in a permanent way.
Extract from Pleased To Meet Me: Genes, Germs And The Curious Forces That Make Us Who We Are, by BILL SULLIVAN published by National Geographic.