Book 1 Reading and Speaking (1108795), страница 25
Текст из файла (страница 25)
For children in rural populations of the developing world, low quality dietslead to poor physical growth, smaller weight and height and high rates of mortality during early life. In these cases,the foods fed to youngsters during and after weaning are often not sufficiently dense in energy and nutrients tomeet the high nutritional needs associated with this period of rapid growth and development.In the industrial world, we are facing the opposite problem: rates of childhood and adult obesity are risingbecause the energy-rich foods we crave—notably those packed with fat and sugar—have become widely availableand relatively inexpensive. According to recent estimates, more than half of adult Americans are overweight orobese. Obesity has also appeared in parts of the developing world where it was virtually unknown less than ageneration ago.
This seeming paradox has emerged as people who grew up malnourished move from rural areasto urban settings where food is more readily available. In some sense, obesity and other common diseases of themodern world are continuations of a tenor that started millions of years ago. We are victims of our own evolutionarysuccess, having developed a calorie-packed diet while minimizing the amount of maintenance energy expended onphysical activity.The magnitude of this imbalance becomes clear when we look at traditionally living human populations.Studies of the Evenki reindeer herders that I have conducted in collaboration with Michael Crawford of theUniversity of Kansas and Ludmila Osipova of the Russian Academy of Sciences in Novosibirsk indicate that theEvenki derive almost half their daily calories from meat, more than 2.5 times the amount consumed by the averageAmerican.
Yet when we compare Evenki men with their U.S. peers, they are 20 percent leaner and havecholesterol levels that are 30 percent lower.These differences partly reflect the compositions of the diets. Although the Evenki diet is high in meat, it isrelatively low in fat (about 20 percent of their dietary energy comes from fat, compared with 35 percent in theaverage U.S. diet), because free-ranging animals such as reindeer have less body fat than cattle and other feedlotanimals do. The composition of the fat is also different in free-ranging animals, tending to be lower in saturated fatsand higher in the polyunsaturated fatty acids that protect against heart disease.
More important, however, theEvenki way of life necessitates a much higher level of energy expenditure.Thus, it is not just changes in diet that have created many of our pervasive health problems but theinteraction of shifting diets and changing lifestyles. Too often modern health problems are portrayed as the result ofeating “bad” foods that are departures from the natural human diet.
This is a fundamentally flawed approach toassessing human nutritional needs. Our species was not designed to subsist on a single, optimal diet. What isremarkable about human beings is the extraordinary variety of what we eat. We have been able to thrive in almostevery ecosystem on the earth, consuming diets ranging from almost all animal foods among populations of theArctic to primarily tubers and cereal grains among populations in the high Andes. Indeed, the hallmarks of humanevolution have been the diversity of strategies that we have developed to create diets that meet our distinctivemetabolic requirements and the ever increasing efficiency with which we extract energy and nutrients from theenvironment.
(Feature article, abridged. From Scientific American, December 2002)56Exercise 3. Which is the best summary of the text? Why?Can you suggest your own variant of the summary?A. Scientific interest in the evolution of human nutritional requirements has a long history. Some scientistsargued that the prevalence in modern societies of many chronic diseases—obesity, hypertension, coronaryheart disease and diabetes, among them—is the consequence of a mismatch between modern dietarypatterns and the type of diet that our species evolved to eat as prehistoric hunter-gatherers. Since then,however, understanding of the evolution of human nutritional needs has advanced considerably—thanks tonew comparative analyses of traditionally living human populations and other primates—and a morenuanced picture has emerged.
We now know that humans have evolved not to subsist on a single,Paleolithic diet but to be flexible eaters, an insight that has important implications for the current debateover what people today should eat in order to be healthy. The challenge our modern societies now face isbalancing the calories we consume with the calories we burn.B. Contemporary human populations the world over have diets richer in calories and nutrients than those ofour cousins, the great apes. Differences in the settings in which humans and apes evolved may helpexplain the variation in costs of movement.
Chimps, gorillas and orangutans evolved in and continue tooccupy dense forests where only a mile or so of trekking over the course of the day is all that is needed tofind enough to eat. Much of early hominid evolution, on the other hand, took place in more open woodlandand grassland, where sustenance is harder to come by. Thus, for far-ranging foragers, cost-effectivewalking saves many calories in maintenance energy needs—calories that can instead go towardreproduction.
Selection for energetically efficient locomotion is therefore likely to be more intense amongfar-ranging animals because they have the most to gain.Exercise 4. You are going to interview your fellow-students. Make up 15 questions about the key factsdiscussed in the article.Exercise 5. Fruits and vegetables in our diet.Discuss the following questions:1.
What is the role of fruits and vegetables in a healthy diet?2. Should we cook vegetables or eat them raw? Why?3. Which cooking techniques allow to preserve healthy substances found in fruits and vegetables and which,on the contrary, can produce negative effects on one’s health?Exercise 6. Read the article below to check some of your answers in Exercise 5.Raw veggies are healthier than cooked onesDo vegetables lose their nutritional value when heated?By Sushma SubramanianCooking is crucial to our diets. It helps us digest food without expending huge amounts of energy.
It softensfood, such as cellulose fiber and raw meat, that our small teeth, weak jaws and digestive systems aren't equippedto handle. And while we might hear from raw foodists that cooking kills vitamins and minerals in food (while alsodenaturing enzymes that aid digestion), it turns out raw vegetables are not always healthier.A study published in The British Journal of Nutrition last year found that a group of 198 subjects who followeda strict raw food diet had normal levels of vitamin A and relatively high levels of beta-carotene (an antioxidant foundin dark green and yellow fruits and vegetables), but low levels of the antioxidant lycopene. Lycopene is a redpigment found predominantly in tomatoes and other rosy fruits such as watermelon, pink guava, red bell pepperand papaya. Several studies conducted in recent years (at Harvard Medical School, among others) have linkedhigh intake of lycopene with a lower risk of cancer and heart attacks.
Rui Hai Liu, an associate professor of foodscience at Cornell University who has researched lycopene, says that it may be an even more potent antioxidantthan vitamin C.One 2002 study he did (published in the Journal of Agriculture and Food Chemistry) found that cookingactually boosts the amount of lycopene in tomatoes. He reports that the level of one type of lycopene, cis-lycopene,in tomatoes rose 35 percent after he cooked them for 30 minutes at 190.4 degrees Fahrenheit (88 degreesCelsius).
The reason, he says: the heat breaks down the plants' thick cell walls and aids the body's uptake of somenutrients that are bound to those cell walls.Cooked carrots, spinach, mushrooms, asparagus, cabbage, peppers and many other vegetables also supplymore antioxidants, such as carotenoids and ferulic acid, to the body than they do when raw, Liu says. At least, thatis, if they're boiled or steamed. A January 2008 report in the Journal of Agriculture and Food Chemistry said thatboiling and steaming better preserves antioxidants, particularly carotenoid, in carrots, zucchini and broccoli, thanfrying, though boiling was deemed the best.
The researchers studied the impact of the various cooking techniqueson compounds such as carotenoids, ascorbic acid and polyphenols.Deep fried foods are notorious sources of free radicals, caused by oil being continuously oxidized when it isheated at high temperatures. These radicals, which are highly reactive because they have at least one unpaired57electron, can injure cells in the body. The antioxidants in the oil and the vegetables get used up during frying instabilizing the cycle of oxidation.Another study published in the Journal of Agricultural and Food Chemistry in 2002 showed that cookingcarrots increases their level of beta-carotene.
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