BITTER TRUTH
how we’re making fruit and veg less healthy by Marta Zaraska
In an effort to cater to our sweet tooth, food producers are making fruit and veg taste less bitter. The trouble is, that's making them worse for us
WHERE have all the white grapefruit gone? When I was a kid, they were almost the only kind around, but today white grapefruit are hard to find in my local shops, often replaced by sweeter pink or red varieties.
I’m not imagining it. Thirty years ago, Florida, the grapefruit capital of North America, produced 27 million boxes of white and 23 million boxes of the coloured varieties. Today, they ship more than twice as many red and pink grapefruit as they do whites ones. And it turns out grapefruit is a bellwether of a more insidious trend. It affects much of the fresh produce aisle, from cauliflower to potatoes, tomatoes and juices. Our fruit and vegetables are becoming less bitter.
On the face of it, reducing bitterness in foods sounds like a great idea. Wouldn’t it be nice if broccoli were always mild and sweet? Supermarkets are already advertising milder Brussels sprouts as “kid friendly”. But there is a catch. The same chemicals that make fruit and veg bitter also imbue them with many of their health benefits. When scientists talk about the healthiness of green tea, dark chocolate, red wine or broccoli, much of what they are talking about is due to bitter chemicals called phytonutrients.
To satisfy our love of sweetness, food manufacturers are now removing many of these substances, causing some people to worry that we are turning bitter fruit and veg into the junk foods of the fresh produce aisle. “Eating fruits and vegetables without phytochemicals would in many ways be analogous to drinking the empty calories of a can of soda,” says Jed Fahey a molecular scientist at Johns Hopkins School of Medicine in Baltimore, Maryland. “Yes, you could survive on de-bittered fruits and vegetables, and they would help maintain life, but not good health.” So if our preference for sweet over bitter is prompting the food industry to strip some foods of the very chemicals that make them good for us, what’s to be done? And how can we train our taste buds to better enjoy bitter?
It makes sense that as consumers we favour sweet ingredients – we have evolved to do so. Sweet foods hold the promise of a ready supply of energy. Salty food contains sodium, necessary for our bodies to function properly. Bitter, on the other hand, suggests toxicity, which is why our natural reaction is to want to spit it out. Bitter phytonutrients act as a natural pesticide, protecting plants against all kinds of enemies, from bacteria to insects and cows. Thousands of these nutrients have been identified so far, giving the bitter tang to familiar foodstuffs such as Brussels sprouts and coffee.
But despite phytonutrients being toxic in large doses, a growing body of evidence suggests that small doses can confer a host of health benefits. The elusive white grapefruit is a prime example. Its most prominent phytonutrient is ultra-bitter naringin, which turns out to have anti-ulcer and anti-inflammatory properties. Naringin can also inhibit the growth of breast cancer cells, and induces cervical cancer cells to commit suicide. The sweeter pink and red varieties have substantially less of the stuff.
The mechanism at work is known as hormesis – simply put, it’s the idea that what doesn’t kill you makes you stronger.
“The reason bitter phytonutrients are cancer preventing is that they can destroy cells. They are healthy because they are toxic,” says Adam Drewnowski, an epidemiologist who studies nutrition at the University of Washington in Seattle. One study, for example, found that eating a diet rich in quercetin, found in green tea, broccoli and red wine, might help protect against lung cancer, especially in heavy smokers.
Sweet tooth
And the list of phytonutrients thought to have anticancer properties is growing. It now includes sinigrin – one of a group called glucosinolates, which give the bitter edge to Brussels sprouts, cauliflower, cabbage and kale (see graphic). There’s also genistein in soya beans, sulforaphane in broccoli, plus potatoes have solanine and tomatoes have tomatine.
Further explanation of the health benefits of phytonutrients may be their antioxidant properties. Antioxidant supplements have come under some scrutiny in recent years. But the thinking is that when eaten as whole foods, rather than supplements, the phytonutrients in bitter fruit and veg trigger our internal antioxidant system to kick in. “These compounds can activate the expression of antioxidant genes that do have the ability to remove oxidants and other potentially toxic compounds,” says Henry Jay Forman of the University of Southern California.
A dose of the bitter stuff seems to have benefits for heart health, too. Phytonutrients in cocoa, coffee or berries can reduce the risk of cardiovascular disease – and not only due to their antioxidant and anti-inflammatory properties. They also help to prevent the build-up of plaque in the arteries.
Even so, we evolved to recoil at the taste of substances that might poison us, rather than favour them for any benefits relating to cancer or heart disease, which usually affect us after we have reproduced. This aversion to bitterness is especially strong in around a third of us. “Because they are bitter, for years we have been removing phytonutrients from the food supply,” says Drewnowski.
As a result, what we eat today is noticeably less bitter than the food our parents and grandparents ate even a few decades ago, says Peter van der Toorn, who leads the vegetable breeding division of Syngenta in the Netherlands. Brussels sprouts are a good example. “We still have bitter sprouts on the market, but the majority of what’s introduced these days is milder.”
Downgraded drinks
One way growers do it is to breed the offending compounds out. In fact, humans have been doing this since the dawn of agriculture. Take tomatoes, a fruit many of us wouldn’t even think of as bitter today. One wild species indigenous to Peru can contain 166 times as much bitter tomatine as the mild varieties we normally find on supermarket shelves.
When breeding and growing conditions are not enough, manufacturers can also sometimes remove bitter compounds later on, instead. They call this process de-bittering.
Citrus juices, for example, naturally contain high amounts of phytonutrients such as limonin, naringin or naringenin. “Most juice manufacturers make a concerted effort to limit bitterness,” says Russell Rouseff, a food chemist at the University of Florida. One method involves passing the juice through a bead-like resin that filters out bitter molecules. This can reduce the amount of naringin in grapefruit juice by as much as 64.5 per cent. Surprisingly, home-made freshly squeezed orange juice contains on average fewer healthy phytonutrients than do commercial freshly squeezed juices. That’s because these producers scrape out more phytonutrient-rich peel oils into the drink.
The more we learn about the role of bitter in our diets, the further the effects seem to reach. Drinking cocoa high in flavanols over a period of four weeks has been shown to significantly increase the presence of bacteria in the gut that boost digestion and immune function. These benefits weren’t seen with “dutched” cocoa, which has had the flavanols removed.
Some de-bittering processes are stripping our food not only of the health benefits bestowed by phytonutrients, but also essential vitamins. What’s more, skimping on bitter could have unwanted effects on our waistlines. “Bitter receptors, which are amazingly spread along the gastrointestinal tract and not only on the tongue, are now known to play a pivotal role in many gastrointestinal mechanisms, such as appetite regulation,” says Daniele Del Rio at the University of Parma in Italy. “Therefore, getting rid of bitter compounds, besides depriving our body of potentially protective phytonutrients, is also impairing our capacity to regulate food intake.”
Many scientists working in the field believe that the food industry has a responsibility to make sure that phytonutrients are preserved in our food supply. It would be better for our overall health if we stopped de-bittering our juices and growing increasingly less-bitter vegetables, Fahey says. This would also help safeguard the genetic diversity of our fruit and veg, which is being lost “at an astonishing rate”.
Such a message isn’t always welcome. Some of those working in the food industry argue that they are simply responding to customer needs.
Yet, as consumers become more interested in the health benefits of bitter phytonutrients, the industry is starting to offer foods enriched with these compounds. Beneforte broccoli, for instance, is bred in the UK for its high content of cancer-fighting sulforaphane.
You could argue that a trend towards milder, sweeter produce is beneficial if it means people eat more fruit and vegetables. “If someone who normally only eats fresh fruit or veg once every three days now eats one a day, because of the less bitter taste, would that be a desirable outcome? I suspect that it might,” says Fahey. That’s especially true of children, who generally have a particularly strong aversion to bitter foods.
Still, this approach is not ideal. “Broccoli, for example, will have a number of things that are good for health: low energy density, fibre, vitamin C. But it also has a number of antioxidant phytonutrients, and if those are bred out, the health function of broccoli will diminish,” Drewnowski says.
So it would be even better to find ways to learn to love bitter food a little bit more. One approach is to start young – as with babies fed hydrolysed casein baby formula, a substance so potent that many adults vomit after trying it. Babies who are allergic to cow’s milk are given this formula, and it’s healthy but bitter. “This stuff is absolutely awful,” says Gary Beauchamp from Monell Chemical Senses Center in Philadelphia. “But if babies are fed it early in life, they don’t mind it, and they will like bitter for the rest of their lives.” That’s been borne out in research showing that kids fed the casein formula at a young age enjoy broccoli more as toddlers than those who grew up on regular, sweet milk formulas.
Acquired taste
With a bit of persistence older children will take to bitter, too, according to research that shows they have to be offered a new food 10 to 15 times before they start liking it. “The child doesn’t even have to eat the food. Repeated exposure is all parents need to do,” says psychologist Gemma Witcomb, who studies children’s eating habits at Loughborough University in the UK.
“Children need to be offered a new food 10 to 15 times before they start liking it”
Adults, too, can change their ways, not least because an affinity for bitter is partly cultural. The first sip of coffee or beer for most people is lip-curling, but many of us learn to love them because their bitterness is paired with a desirable hit: caffeine or alcohol.
A similar approach could help make more virtuous bitter foods more palatable too, thanks to something called flavour-flavour learning – pairing something you don’t like with something you do like. Both children and adults who drank grapefruit juice mixed with sugar, and ate broccoli with sugar sprinkled on top, learned to like the bitter foods, even without the sugar. And there are ways to cook food to balance out or compliment the bitter tastes.
This goes to show that with a bit of effort we can all change our approach to bitter food. As for sourcing the right ingredients, keep an eye out for heritage varieties, with all their healthy bitterness. But more than anything, just let your taste buds guide you. Whether you learn to like the non-dutched cocoa full of flavanols, or come to seek out white grapefruit that’s stuffed with naringin – the more bitter the better.
From the New Scientist, 29/7/'15.
From the New Scientist, 29/7/'15.
