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Whether this spread looks appetizing or disgusting to you make have a lot to do with your genes. Image Credit: dboy, Flickr

Why do some people love broccoli, kale and black coffee, while others hold their noses when faced with these bitter-tasting foods? New research published in the journal Chemical Senses this month may help get at the answer.

Our evolutionary history plays a huge role in which flavors we like and which we avoid. Find it impossible to resist that office birthday cake, even though you know you shouldn’t indulge? The excellent cookbook/food science guide Cooking for Geeksinforms me that we probably love fats, sweets and sugars because back when we were hunting and gathering, the foods they were found in (I’m thinking things like ripe wild strawberries and woolly mammoth meat), were tough to get and also high in energy.

Because of these nutritional advantages, fewer of those who had no affinity survived to pass on their genes. However, in the modern landscape of Big Gulps and Applebee’s restaurants, our evolved love of fats, sweets and sugars now works agasint us, and the result is the obesity epidemic.

Almost everybody likes cake and candy bars. But this isn’t true for bitter foods (although many people do seem to acquire a taste for them as they grow up). According to the new paper, we have 25 “bitter” taste receptors, each with its own gene. But all of them aren’t expressed in all of us: which of them are turned on varies wildly from person to person, much more so than for other taste receptors like those for sweet or salty flavors. The paper suggests that this may be due to “local adaptation to the avoidance of plant toxins;” in other words, if your hunting-and-gathering territory included a lot of bitter plants which were also poisonous, the genes of your ancestors would reflect a distaste for the flavor.

The study tested how which versions of the “bitterness genes” a group of 96 subjects had related to their sensitivity to bitter flavors. The participants were given a genetic analysis, and also a taste trial, in which they sampled espresso, scotch whiskey, and unsweetened grapefruit juice and were asked to rank how strongly they liked or disliked the flavor. They found a strong relationship between genes and affinity for bitter flavors: participants who had one version of a certain gene, for example, ranked grapefruit juice as tasting twice as bitter as participants with a different version.

Each of the 25 “bitterness genes” seem to control our liking for different foods. “This study moves us beyond the one-size-fits-all approach,” said lead researcher John Hayes in a press release. “It turns out that different bitter foods act through different receptors, and people can be high or low responders for one but not another. Thus, you may despise grapefruit but have no problem with black coffee.”

Hayes explains that bitter and sweet tastes work in opposition in the brain — so if you perceive a food as tasting more bitter, then it also tastes less sweet to you. “This means not all foods taste the same to all people,” said Hayes. Perhaps this provides insight into why some people are picky eaters and others aren’t.

These genetically-determined taste preferences appear to have real affects in our diets. According to Hayes, people who are more sensitive to bitter tastes eat 25% fewer vegetables, which could put them at greater risk for certain diseases like colon cancer. The study also found that having the “less sensitive” version (called K172) of one of these genes appears to be a risk factor for drinking too much alcohol (alcohol, if you think about it, has a distinctly bitter taste).

If subsequent research backs up these findings, it seems that our tastes may be more influenced by our genes than we thought. If you have a lifelong loathing of spinach and dark chocolate, your picky tastes might be due to a super-sensitivity to bitter flavors. Go ahead and blame your genes if you want, but this research doesn’t give you a pass: veggies are still good for you.

 

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Case 4.  This was a normal term infant born to a Jewish mother of Iraqi origin. Before delivery, the amniotic fluid was reported to be “yellow and foul smelling”. The baby had a yellowish skin discolouration similar to mecomium staining, and a peculiar odor. Blood cultures from the infant and amniotic fluid cultures were obtained, and antibiotics were administered. On re-examination, the peculiar odour was judged to be identical to that of curry.

This is an excerpt from a report that appeared in The European Journal of Pediatrics in 1985 called “Peculiar odors in newborns and maternal prenatal ingestion of spicy food.” It details four case studies.  In each one, an infant was born, and after doctors and parents had joyfully ascertained that it had two eyes and all the necessary appendages, something else became apparent… the baby smelled a little funky.

Two of the odiferous infants smelled of cumin, one of curry, and one of something called fenugreek (a flowering plant that is a common ingredient in many curries and an herbal remedy for a variety of health conditions). The doctors were concerned because a smelly baby can be a bad sign: strange odors can indicate dangerous conditions such as Maple Syrup Disease, a genetic disorder that causes a buildup of certain amino acids (and the eponymous odor) which can be fatal if untreated.

As it turns out, the stinky newborns weren’t sick: the source of their mysterious odors was pungent, spicy foods their mothers had enjoyed just prior to delivery.  According to the report, “The spices were absorbed from the maternal gastrointestinal tract and transferred to the amniotic fluid, where they were swallowed by the fetus.” It seems that babies can experience mom’s dinner choices directly, and if they don’t like curry, well, that’s just too bad.

Subsequent studies have shown the significance of the mother’s diet on the baby’s environment. In a 1995 study, a group of pregnant women downed garlic pills, then had some smell-testers compare the odor of those women’s amniotic fluid to that of a control group. The testers had no trouble detecting which mothers were garlic-eaters.

And it seems that what the mother eats during pregnancy can actually shape the baby’s future taste preferences. A 2000 paper from the journal Chemical Senses shows that infants whose mothers who ate anise during pregnancy exhibited a preference for the flavor (which has a strong licorice flavor and is not universally liked) after birth. It seems that our tastes start being shaped in the womb (perhaps explaining why we tend to be partial to the foods of our homelands).

However, the strong influence of our mothers’ tastes isn’t always a good thing.

A 2007 study from the British Journal of Medicine showed that pregnant rats fed a “junk food” diet (lots of fats, sugars, and salts) gave birth to babies who showed a preference for a junk food diet throughout life, and as a result, often grew obese. This is especially frightening considering that pregnancy cravings often demand things like ice cream and greasy Chinese takeout.

All in all, mom’s diet seems to affect baby in some intriguing (and amusing) ways. One thing seems certain: if you’re a pregnant woman nearing your due date, you might want to resist those pickle cravings, lest your offspring emerge smelling like a kosher dill.

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