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.New Scientist:
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.
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.
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".
It is easy, but unfair, to blame the food industry. Growers and retailers are only responding to consumer demand. But how many consumers have heard of de-bittering? Can you demand something you don’t know about? The real culprit is a lack of reliable information, fueled by well-meaning but counterproductive rules on food labeling.