Diets to Ward Off Diabetes | Science News

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Food for Thought

Janet Raloff
Food for Thought

Diets to Ward Off Diabetes

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Some 16 million people in the United States have type 2 diabetes, which used to be called the disorder's "adult onset" form. In fact, its incidence has been skyrocketing, climbing by nearly 50 percent over the past decade alone. Even children are now developing type 2 diabetes, which is characterized by the body's resistance to insulin, the hormone that shepherds energy into cells.

At least as worrisome, some 16 million more people in the United States exhibit so-called prediabetic symptoms—less serious insulin resistance and sometimes other features of the body's impaired processing of digested food. There is some good news, however: Several new studies suggest that simple lifestyle changes can reap big benefits in delaying—and possibly preventing—the eventual development of type 2 diabetes in this huge at-risk population.

For instance, walking briskly for 30 minutes five times a week can halve prediabetic individuals' risk of developing full-blown disease. In addition, eating smaller, more frequent meals—especially those containing foods that break down slowly—can slow an individual's progression to diabetes.

In a move to encourage such lifestyle changes, the Department of Health and Human Services launched its first National Diabetes Prevention Campaign on Nov. 20.

"You don't have to be a marathon runner or starve yourself to prevent diabetes," notes HHS Secretary Tommy G. Thompson, because small changes can "translate into big rewards." Indeed, that's why his agency dubbed its campaign "Small Steps, Big Rewards."

Two new studies point to a few foods that may boost the ability of any diet to protect a person with prediabetic symptoms. Don't panic: We're not talking about adding mounds of Brussels sprouts and liver to your plate. In fact, the new data would appear to give us license to indulge a little more heavily in things most people already love: coffee, nuts, and peanut butter.

A stimulating find

At least in the United States, coffee has developed a two-edged reputation. It's the morning pick-me-up of choice, the excuse for taking a break with friends, and a cultivated finish to fine meals. However, because coffee naturally possesses the powerful stimulant caffeine, some physicians caution their heart patients to eschew the brew.

Moreover, if it's brewed without a filter, coffee can contain oils that spike cholesterol concentrations in an person's blood. And studies have shown that drinking even filtered coffee can increase blood concentrations of an amino acid—homocysteine—that poses an extra risk of heart disease. One study found that people who down four or more cups of coffee daily face double the normal risk of rheumatoid arthritis.

However, Rob M. van Dam and Edith J.M. Feskens of the Dutch National Institute of Public Health and the Environment now report that when it comes to diabetes risk, the more java you down, the better you fare.

They surveyed nutritional data collected periodically from a huge group of Dutch men and women who were participating in a long-running general-health study. Van Dam and Feskens restricted their analyses to the 17,000 individuals who didn't have diabetes when they were recruited between 1987 and 1997. During follow-up surveys, 306 individuals reported having developed the type 2 form of the disease. The researchers then compared the incidence of this diabetes among segments of the populations with various coffee-drinking habits.

In the Nov. 9 Lancet, van Dam and Feskens report finding a dramatic protective effect of the brew that increased with the amount people downed each day. More importantly, van Dam notes, the protective effect showed up even after the researchers adjusted their data to account for other type 2 diabetes risk factors among the volunteers, including heart disease, high blood pressure, age, weight, and gender.

Indeed, after that change, the apparent protective effect of coffee only strengthened. The data indicate that people drinking 3 to 4 cups per day had only 79 percent of the risk of developing diabetes as did study participants drinking 2 or fewer cups daily. In people quaffing 5 to 6 cups a day, the risk dropped to just 73 percent. And among those downing a whopping 7 or more cups daily, the diabetes rate dropped to just half of that among people drinking no more than 2 cups a day.

To many Americans, the idea of downing a jolting 7 cups of coffee every 24 hours may seem excessive. However, van Dam notes, nearly one-quarter of Dutch people do that.

What made these researchers look at coffee's potential role in type 2 diabetes in the first place? Although research has shown that caffeine can impair the body's ability to manage glucose, van Dam observes that several studies reported that drinking coffee—the whole brew, not just the caffeine—seems to improve glucose control and a person's sensitivity to insulin.

What those short-term studies couldn't establish, however, was whether such changes actually played a role in warding off diabetes. So his group investigated that in a huge, ongoing study of aging Dutch adults.

This is nutty

Researchers at the Harvard School of Public Health have for many years been mining huge, long-running studies for similar types of associations between diet and disease. Their latest finding, published in the Nov. 27 Journal of the American Medical Association, found a similar dose-response relationship between reported nut consumption and type 2 diabetes risk.

This study focused on data from almost 84,000 women in the Nurses' Health Study, which Harvard researchers began in 1980. At the beginning of their participation and periodically ever since, the recruits have filled out surveys describing their eating habits.

Although nuts can derive up to 80 percent of their calories from fat, much, if not most, of that fat is unsaturated—a type that can have a number of health benefits for a body's control of glucose and insulin. Nuts also offer substantial fiber and magnesium, two food constituents that in other studies appeared to protect people from type 2 diabetes. However, until this new study, researchers had never probed whether nuts actually alter diabetes incidence.

And they appear to, mightily. Compared with women who reported seldom eating nuts, those who ate 1 to 4 ounces per week had a 16 percent reduction in diabetes risk. Those eating at least five servings—or 5 ounces—weekly exhibited a 27 percent reduction in disease incidence, compared with the first group.

Because one of the most popular nutty offerings, peanut butter, doesn't come from a true nut (peanuts are legumes), Frank Hu and his colleagues probed for any benefit from it as well.

They found one: Women who had been eating at least 5 ounces of peanut butter a week had a 20 percent lower incidence of diabetes than did women who seldom or never indulged in the fatty sandwich spread.

In this study, too, the dietary protection against diabetes appeared to hold up even after accounting for other factors predisposing people to type 2 diabetes. However, because too much fat isn't healthy for the heart and can contribute to weight gain, itself a diabetes risk factor, study coauthor Rui Jiang recommends that "people should not simply add nuts on the top of the diet. Instead, people should substitute nuts for less healthy foods, such as refined carbohydrates like white bread and red meats."

How might foods be protective?

The body needs insulin, a hormone, to use glucose, a sugar that's liberated during the breakdown of foods. The hormone normally shepherds glucose into cells, where the sugar is consumed as fuel. With type 2 diabetes, however, the body ignores much of its insulin. This leaves too much glucose in the blood and many cells hungry.

The body responds by making more insulin, much of which still goes ignored. The blood's excess of insulin and glucose can damage organs, which is why doctors and nutritionists relentlessly harangue their patients to carefully manage blood sugar through diet and/or drugs.

One piece of advice that dieticians and endocrinologists have increasingly offered people with prediabetic symptoms is to favor foods with a low glycemic index—that is, foods that break down into glucose relatively slowly (SN: 4/8/00, p. 236:The New GI Tracts). It turns out that nuts are among such foods.

However, the Harvard team points out, its analysis indicates that the apparent benefit of nuts was not explained entirely by their fat, fiber, and magnesium. Hence, the researchers speculate, other constituents of nuts "or interactions among these factors may also play important roles in reducing the risk of type 2 diabetes."

Van Dam suspects that a relatively minor constituent of coffee, chlorogenic acid, may explain much of the drink's apparent antidiabetic benefit. This chemical, which plays an important metabolic role in many plants, is perhaps best known as the agent that fosters the darkening of a raw potato once it's exposed to air. For heavy coffee drinkers, van Dam notes, java may serve as the primary and most consistent source of chlorogenic acid in their diet.

Lab studies of human cells indicate that in the liver, chlorogenic acid can inhibit the secretion of glucose. If the chemical does that in a coffee drinker, van Dam says, "it could reduce glucose levels in the blood and thus offer a quite plausible hypothesis for coffee's apparent protective effect" against type 2 diabetes.

Van Dam says he hopes to explore that possibility in a short-term trial that gives chlorogenic acid pills to people who don't drink coffee. He'd also like to explore whether decaffeinated coffee has a benefit similar to that of the regular brew.

At a news briefing unveiling HHS' new diabetes-prevention campaign, Francine Kaufman, president of the American Diabetes Association argued, "Now that science has demonstrated that type 2 diabetes can be prevented or delayed, it is imperative that the American Diabetes Association work together with Secretary Thompson, the National Diabetes Education Program, and its many partner organizations to begin to reach people at risk with the hopeful news."

A high priority, said Kaufman, should be targeting this news to parents. Even a decade ago, she noted, type 2 diabetes in children was "an almost unheard of phenomenon." With obesity and, therefore, the risk of this disease rising in all age groups, she said, "increasing awareness of type 2 diabetes prevention is essential?not just for adults, but for our children as well."

Citations

Francine Kaufman
American Diabetes Association
1701 North Beauregard Street
Alexandria, VA 22311
Phone: 1-800-DIABETES
Web site: [Go to].

Frank Hu and Rui Jiang
Department of Nutrition
Harvard School of Public Health
665 Huntington Avenue
Boston, MA 02115

Tommy G. Thompson
U.S. Department of Health and Human Services
200 Independence Avenue, S.W.
Washington, DC 20201

Rob M. van Dam
Department of Nutrition and Health
Faculty of Earth and Life Sciences
Vrije Universiteit Amsterdam
De Boelelaan 1085
1081 HV Amsterdam
The Netherlands
E-mail: robvdam@bio.vu.nl

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