The Scientific Reason Some People Can’t Stand Vegetables
And what it takes to overcome an aversion to bitter greens
Bitterness is nature’s way of warning us about harmful things we shouldn’t eat, like cyanide. But several very healthy foods, including broccoli and cauliflower, are bitter, too — which makes them disgustingly inedible to some people, but not to others. You haters can blame your genes, studies show. And while you can’t change your genes, you might be able to overcome your distaste if you’re willing to try, try again. After all, it works with coffee. (And beer.)
Scientists have known for many years that some people have a genetic aversion to bitter vegetables. One in five find them unbearable, says Clare Collins, PhD, a professor in nutrition and dietetics at the University of Newcastle in Australia. These are what researchers call super-tasters. If you inherited super-taster genes, then those flowering cruciferous vegetables, which also include bok choy and Brussels sprouts, “will taste disgusting,” Collins explains.
Cruciferous vegetables are loaded with nutrients, from beta-carotene to vitamins C, E, and K, and they’re a good fiber source. But they’re also packed with glucosinolate, which produces a bitter oil when cut, chewed, or cooked.
Roughly 30% of people don’t sense the bitterness at all. These people have two copies of a gene variant called AVI, explains Jennifer Smith, PhD, a postdoctoral fellow in cardiovascular science at the University of Kentucky School of Medicine. People with one AVI and one PAV variant taste bitterness more than some people but less than others. The super-tasters have two PAVs. “We’re talking a ruin-your-day level of bitter,” Smith says.
Smith’s preliminary new research, being presented at this year’s meeting of the American Heart Association, involved people at risk for cardiovascular disease, who really should be eating their veggies. It compared their genetic profiles, via analysis of their saliva, to what they ate, based on questionnaires. People with two PAVs were more than 2.5 times as likely to be in the bottom half of a list ranking everyone in the study by the quantity of vegetables they eat. “We hypothesize that this is because the vegetables taste bitter,” based on the prior research showing that the PAV variant “is strongly associated with enhanced bitter taste,” Smith says.
Get used to it
If you can stomach the effort, downing some broccoli again and again could actually make it taste better, according to a study earlier this year in the journal Chemical Senses. The research, done with rats, found that eating bitter vegetables repeatedly changes the mix of proteins in saliva, leading to a change in what the taste buds perceive. These proteins are thought to either bind to flavor compounds in food or to taste receptors in the mouth.
“When you eat a food, it is a complex mixture of tastes — bitter, sweet, and salt may all be present,” says study team member Ann-Marie Torregrossa, PhD, an assistant professor of psychology at the University at Buffalo. “We believe that as the salivary proteins are altered, the bitter taste is less strong but the others may be unaffected. So the food tastes less bitter and likely tastes better.”
“If we can convince people to try broccoli, greens, and bitter foods, they should know that with repeated exposure, they’ll taste better.”
Torregrossa says the process is not unlike how young people might detest their first sip of coffee or beer — both of which are bitter — yet ultimately develop a liking. (Other researchers note that culture and environment also play a role in whether people ingest bitter things.)
So, how many servings of bitter greens would it take to overcome an aversion? “Ha! The million-dollar question,” Torregrossa replies.
Other research by Cordelia Running, PhD, an assistant professor of nutrition at Purdue University, is beginning to answer this question. Running wondered if human tastes changed similarly to the rats. Her team had people drink chocolate almond milk three times a day for a week, rating its bitterness each time. As the mix of proteins in their saliva changed, the ratings on bitterness went down. Along with other research, this finding supports the idea that “saliva modifies flavor, which in turn modifies dietary choices,” Running says.
And that’s important, all these researchers say, because vegetables are one key to a healthy, balanced diet. Diets rich in fruits and veggies can help lower blood pressure, lessen the risk of heart attack and stroke, and even help prevent some cancers and battle depression.
So why, from an evolutionary standpoint, do so many people hate so many vegetables? It could be because glucosinolate — the bitter chemical — actually can serve as a warning. Apple seeds are one example of something bitter that can be harmful. They contain amygdalin, a bitter chemical that turns into cyanide when the seeds are chewed or crushed (you’d have to eat dozens or hundreds of seeds to die from them).
If you like coffee…
Here is a clear example of people getting used to a bitter taste when there’s some benefit — even joy — involved: A study last year found that people who are the most sensitive to the bitter taste of caffeine, based on their genes, actually drink more coffee than other individuals — not because of that bitterness, but despite it.
“You’d expect that people who are particularly sensitive to the bitter taste of caffeine would drink less coffee,” says study leader Marilyn Cornelis, PhD, assistant professor of preventive medicine at Northwestern University Feinberg School of Medicine. Since the opposite was found, Cornelis suggests people acquire a taste for coffee because of the stimulating effect of the caffeine. In other words, it’s worth the effort. The finding, detailed in Scientific Reports, suggests it is “very possible” that people who find certain vegetables bitter could, in fact, get used to them, Cornelis says.
“Genetics only partly determine taste/food preferences.” If you’re concerned about getting enough veggies for you or your kids, Collins, the nutritionist, suggests adding cheese, onions, herbs, or spices like salt, pepper, or chili to mask the bitterness of vegetables. Or try vegetables that are less bitter, such as lettuce, peas, carrots, and eggplant. Or just dig in. “If we can convince people to try broccoli, greens, and bitter foods, they should know that with repeated exposure, they’ll taste better,” Torregrossa says.
