March 3, 1998
New York Times
Adding Cumin to the Curry: A Matter of Life and Death
By JANE E. BRODY
hoose any and all correct statements:
People living in hot climates eat lots of highly seasoned foods because --
1. Hot spices cool them down by making them sweat.
2. Food spoils faster in hot climates and potent seasonings disguise the taste and smell of spoiled food.
3. Spices grow profusely in the tropics and it is cheaper and easier for people to eat what is locally available.
4. Spices provide important nutrients that might otherwise be in short supply in these areas.
5. Spices make foods taste better and increase consumption of nutritious but not necessarily appealing foods.
6. Pungent spices are natural preservatives that inhibit food spoilage.
If you choose any of the first four statements, logical as they may seem, two Cornell University researchers say you would be wrong. In a paper published this month in "The Quarterly Review of Biology," Jennifer Billing and Paul W. Sherman argue that "some like it hot" because spice plants contain powerful antibiotic chemicals capable of killing or suppressing the bacteria and fungi that commonly contaminate and spoil foods and can poison those who eat them.
Spices that are prominent in traditional dishes from tropical and subtropical regions are used with a much lighter hand, if at all, in countries and regions where the climate is colder, the researchers found. And many of the spices that appear most often and most abundantly in recipes from hot climates -- especially garlic, onion and hot peppers -- can inhibit 75 percent to 100 percent of the bacteria species against which they have been tested, according to studies by food microbiologists.
The researchers concluded that a taste for spicy foods may have evolved in hot climates and been transmitted from neighbor to neighbor and to succeeding generations as a cultural "neme," the social science equivalent of a gene. While they admit that the immediate reason for using spices "obviously is to enhance food palatability," they added that "the ultimate reason is most likely that spices help cleanse foods of pathogens and thereby contribute to the health, longevity and reproductive success of people who find their flavors enjoyable."
George Williams, the editor of the journal, said that transmission of a taste for highly spiced food is both cultural and genetic and can begin in the womb. He cited studies by Sandra Gray at the University of Kansas showing that "the mother's diet during pregnancy and lactation can influence the dietary habits of her baby throughout its life."
Of course, Sherman said in an interview, people have other ways than spices of preserving food -- by salting, cooking, smoking, or drying it, and now by refrigerating or freezing it.
But he believes the contribution of spices, all of which come from plants, had not previously been adequately explored or appreciated. He pointed out that many spice plants are rich in compounds that have antimicrobial actions. These compounds evolved in plants as protection against pathogens and predators.
Thomas Eisner, professor of chemical ecology at Cornell who has studied how animals use plant chemicals, said, "Many plant metabolites have antimicrobial potency. The use of antibiotics from natural sources is by no means a human invention." For example, he said, an assassin bug he has studied scrapes resin from the leaves of camphor weed and spreads it on her eggs to protect them from pathogens.
Sherman, an evolutionary behaviorist and professor of neurology and behavior, and Ms. Billing, then an undergraduate at Cornell, analyzed the frequency with which various spices appear in the traditional recipes of 36 countries, including the northern and southern halves of the United States and China.
In the analysis of 4,578 recipes containing meat, poultry or fish published in 93 traditional cookbooks, Ms. Billing found that the hotter the climate of the region, the more spices were called for in the recipes.
Especially prominent were spices like onion and garlic that have been shown to inhibit the growth of all 30 microorganisms considered in the study. Capsicums, or hot peppers, which are widely used in hot climates, inhibit the growth of 80 percent of microorganisms considered.
For example, among 120 recipes from Indonesia, 80 percent contained garlic and onion and 77 percent contained capsicums. However, in Ireland, a considerably cooler country, onions appeared in 56 percent, garlic in 23 percent, and capsicums in only 2 percent of 90 recipes analyzed, even though the plants can grow there.
In India, more than 80 percent of Indian recipes were prepared with onions, ginger, and capsicums and 76 percent called for garlic.
But in Norway, the only prominent seasonings were black and white pepper, used in less than half the recipes.
Onion appeared in only 20 percent of recipes and capsicums were not found in any of the 77 traditional recipes analyzed.
Likewise, there are spice use differences within countries with significant regional temperature differences: the northern and southern United States and northeastern and southwestern China. Sherman suggested that antimicrobial activity may explain why a relatively bland milk-based clam chowder became popular in New England while a spicier crawfish etoufee is preferred in the Deep South.
"I consider recipes a record of the cultural co-evolutionary race between us and microbes," Sherman said. "We are trying to keep ahead of the microbes that are trying to eat the same foods we eat."
He outlined a likely scenario for the evolution of highly spiced foods in countries where food-borne microbes thrive: "The first spice is added and it has a positive effect. Then a second microbe comes along and another spice is added, which has a positive effect, and so on, until a lot of spices are being used, but not so many that there are negative consequences."
He also noted that many spices that themselves have relatively weak antibiotic effects become much more potent when combined, for example, in chili powder (typically a mixture of red pepper, onion, paprika, garlic, cumin, and oregano) and five-spice powder (pepper, cinnamon, anise, fennel and cloves). Lemon and lime juice, too, have such synergistic effects, Sherman said.
Cheryl Ritenbaugh, an anthropologist who studies how food influences health at the Kaiser-Permanente Center for Health Research in Portland, pointed out that chili peppers are a New World food that did not circulate worldwide until after the time of Columbus, so their use in many tropical countries may be too recent to support the Billing-Sherman theory.
However, she said: "If the climate is hot and the food monotonous, people may not eat enough, and anything that would add flavor and kill bacteria would be very welcome."
Spicy foods may also enhance digestion. Marvin Harris, an anthropologist at the University of Florida in Gainesville, said foods made with chili peppers increase salivation, prepare the gut for receiving food, foster intestinal action and help to create a sense of fullness, which would be an evolutionary advantage in countries where food was relatively scarce.
Larry R. Beuchat, a microbiologist who studies food-borne pathogens and spoilage organisms at the University of Georgia's Center for Food Safety and Quality Enhancement in Griffin, Ga., said that the Billing-Sherman hypothesis has merit. Even at the low levels used in recipes, plant chemicals have antimicrobial activity, he said, adding that the use of essential oils, which are oil-based extracts of plant chemicals, "is one of the oldest methods of preserving meat and was used in mummification."
Sherman pointed out that in large quantities, some of the antimicrobial chemicals found in spice plants are mutagens, carcinogens, and teratogens, substances that can cause genetic damage and birth defects. This may be why women in the first trimester of pregnancy and children who are growing rapidly tend to avoid spicy foods, he said. "During rapid growth, even though there is still a danger of ingesting microbes, the risk of ingesting harmful plant compounds from spices might be worse," he suggested.
Sherman and Ms. Billing discounted competing explanations for the prevalence of spices in foods from hot climates. They wrote that because spices are consumed in tiny quantities, they provide little of nutritive value. Only hot peppers, but not most of the prominently used spices, induce sweating "and even chilies do not increase perspiration in many people."
That the use of spices evolved and spread simply because they disguise the smell or taste of spoiled foods makes little evolutionary sense because people who ate them would be more likely to get sick and die.
The researchers found no relationship between mean annual temperature and numbers of spices that grow in each country. Nor do tropical countries rely only on spices that are locally grown. "People do not use every spice that grows in their country, but they do use many spices that must be imported, and for centuries have gone to great lengths to obtain them," they wrote. Although pepper, for example, is one of the most frequently used spices in all 36 countries studied, it grows in only nine of them.
In further support of their argument, Sherman and Ms. Billing noted that "flavors of many widely used spices are not immediately appealing." Rather, people have to learn to like them. "The fact that parents encourage their children to eat (displeasing) spices, and that children come to prefer them by adolescence, strongly suggests that using spices is somehow beneficial," the researchers said.