Home > Life in Japan > Environment
  print button email button

Thursday, Feb. 20, 2003

NATURAL SELECTIONS

No taste for obesity


In the British cult comic 2000AD, future lawman Judge Dredd patrols the streets of Mega City One, a vast metropolis on the eastern seaboard of what was once the United States. Mega City One makes Tokyo seem spacious, and its residents make Harajuku's weirdest seem tame: One group of future misfits are the Mega City Fatties, citizens whose only goal is to get bigger, heavier and fatter. To help them move their flab, most of the fatties use a belly wheel, a mobile support for their immense guts.

The way the United States is going, the belly wheel might not be fiction for long.

Obesity affects 60 million adult Americans, accounts for at least 300,000 deaths a year and costs $100 billion in health-care. The incidence of obesity has increased by approximately one-third, from 23.3 percent of the population in 1991, to 30.9 percent today. This could be an obesity epidemic. The World Health Organization says it is a leading global health problem.

But the National Institutes of Health in the U.S. annually spends less than 1.0 percent of its budget on obesity research.

The obese face prejudice when trying to gain employment and are discriminated against in other ways, too. Many find it shocking to observe such people indulging in feeding excesses while millions in other parts of the world die from malnutrition.

The truth, though, is that obesity has less to do with sloth and gluttony and more to do with genes and environment. The way humans evolved means we have been selected to respond to different tastes and different foods. Natural selection under one set of conditions, such as in the African savannah, where modern humans arose, will have a different outcome under another set of conditions, such as those in suburban America. Gorging on berries, for example, was probably a useful way of exploiting a short-term food supply and may have led to the selection of individuals with so-called "thrifty genes," which encourage efficient fat storage.

In other words, biology plays a major role in determining our food choices. Love of sugar is almost ubiquitous in mammals. Sugars were relatively rare chemicals in the environment in which we evolved, so we were selected to make the most of them when we did find them. Jelly doughnuts and Coke may provoke the same instinct today, but since there is a long-term supply, gorging on them has a different outcome.

But why do some people gorge and some refrain? The French gastronome Brillat- Savarin wrote: "Tell me what you eat, and I shall tell you what you are," in his 19th-century book, "The Physiology of Taste." Brillat-Savarin was probably thinking that a person eating mainly bread was a peasant and a foie-gras eater was a bourgeois, but scientists reported similar conclusions at last week's annual meeting of the American Association for the Advancement of Science.

Biological differences in our sense of taste have such an influence on our diets that they may help determine which diseases we might be susceptible to, according to research by Linda Bartoshuk of Yale University School of Medicine, Mass. To update Brillat-Savarin, we might say: "Tell me what you eat, and I'll tell you what you'll die of."

Up to a quarter of the population may be at lower risk of obesity because they are genetic "supertasters," said Bartoshuk. Supertasters live in a blazing neon taste world with taste sensations three times as intense as the mere pastel shades of "nontasters," who make up another 25 percent of the population, and "medium-tasters," who make up half. That's because the tongues of supertasters have a higher concentration of taste bud-containing structures than the tongues of less taste-sensitive groups do.

Taste buds also detect the sensations of touch (and therefore mediate pain responses), so supertasters are also the most sensitive to the heat of chillis, for example, and the feel of fat. Women are more likely to be supertasters than men, but supertasters of both sexes are distinguished because they find the chemical 6-n-propylthiouracil so bitter they cannot stand it.

"The ability to taste bitter substances has always been associated with poison detection, but now we have found all these health associations," Bartoshuk said. "We know people's whole diets are different, based on their taste sensitivity."

The first thing Bartoshuk's work shows is that being a picky eater isn't necessarily a sign of a difficult personality.

"Supertasters are picky eaters. They taste bitterness in food that other people don't notice. For some, the food world is just slashing bright and they opt out from many food choices," Bartoshuk said.

Supertasters tend to avoid very sweet, high-fat foods, but are also generally averse to vegetables, which taste unpleasantly bitter to them. As a group, supertasters tend to be thinner, but their veggie aversion may lead to a higher risk of certain cancers, Bartoshuk has found.

Studying the colonoscopies of a group of older men, Bartoshuk and Marc Basson at Wayne State University school of medicine in Michigan found a correlation between the number of polyps and the ability to taste bitterness. The men with more polyps reported eating the fewest vegetables and were heavier, both risk factors for colon cancer.

Bartoshuk and research collaborators have also found a correlation between weight and a history of ear infections that seems to be linked to taste sensitivity, and Valerie Duffy, a colleague of Bartoshuk, has found that supertasters are at less risk for cardiovascular disease, probably because of their lower fat intake.

The genes responsible for nontasting, medium tasting and supertasting may have emerged during evolution because they provided each group with certain health advantages, related to their food preferences, Bartoshuk proposed. Her team has shown in a study of older women containing medium- and supertasters, that those with higher perception of propylthiouracil have less body fat, smaller hips and a lower BMI, a factor expressing obesity.

All this paints a complex picture of diet, genes, health and body weight, but one that might become clearer when we allow for natural selection, for how the food environment was as we were evolving, and for how it is now. Then when the belly wheels start rolling in the United States, the fatties might claim to have evolution on their side.

Rowan Hooper welcomes comments at rowan.hooper@tcd.ie


Back to Top

About us |  Work for us |  Contact us |  Privacy policy |  Link policy |  Registration FAQ
Advertise in japantimes.co.jp.
This site has been optimized for modern browsers. Please make sure that Javascript is enabled in your browser's preferences.
The Japan Times Ltd. All rights reserved.