In 1986, Harvard's Walter Willett and co-workers asked roughly 80,000 female nurses to fill out diet questionnaires. By 1992, 915 of the nurses were diagnosed with non-insulin dependent diabetes, the kind that usually occurs in adults.
Then the researchers used two measures to compare the nurses who were later diagnosed with diabetes with the nurses who weren't: fiber intake and "glycemic load." Glycemic load estimates how much carbohydrate the nurses ate and how much those carbs raised levels of glucose and insulin in their blood.
"In general, less-refined foods like intact whole grains and legumes are less-rapidly digested, so they enter the system more slowly," says Thomas Wolever, a University of Toronto fiber expert. "That dampens down insulin secretion and puts less stress on the system." Less insulin means a lower glycemic load.
In theory, that should lower the risk of diabetes, which occurs when the body secretes more and more insulin as a person's insulin loses its effectiveness.
Willett's results: "We found that the risk of diabetes increased about two-and-a-half-fold in women who had the highest glycemic load and the lowest fiber intake," he says. "Women who ate the most sugar and refined starches, like white bread, pasta, and potatoes, had the highest risk."
But Willett can't say exactly what parts of the foods made the difference. "It looks like fiber has some independent benefit," he says. "But the magnesium or some other nutrients that come with the whole grain may also matter."
So far, it's largely the fiber in whole grains that has caught the attention of heart disease researchers.
For example, in a recent study of more than 43,000 U.S. male dentists, veterinarians, and other health professionals, those who reported eating an average of 29 grams of fiber a day had a 41 percent lower risk of heart attack than those who averaged 12 grams a day. Fiber from grains -rather than fruits or vegetables -- was "most strongly associated with a reduced risk," noted the researchers.
And among nearly 22,000 Finnish men, those who ate roughly 35 grams of fiber a day, much of it from whole grain rye bread, not the refined rye eaten here-had a 31 percent lower risk of heart disease than those who ate an average of 16 grams a day, which is close to the average for American men.
|The Bread & Cracker Box|
Pepperidge Farm Natural Whole Grains Crunchy Grains bread is mostly whole grain. Pepperidge Farm Light Style Seven Grain bread isn't.
Nabisco Reduced Fat Triscuits and Wheat Thins are all or mostly whole grain. Nabisco Wheatsworth crackers aren't.
Marketers seem bent on feeding us white flour while making us think we're eating whole grains. Here are some tips to see through their schemes:
It's mostly reflned grain if the front label says: cracked wheat, made with whole grain, made with whole wheat, multi-grain, oat bran, oatmeal, pumpernickel, rye (breads), seven-bran, 12-bran, etc., seven-grain, nine-grain, etc., stoned wheat, wheat, wheatberry, whole bran.
"We see an effect of fiber," says Willett, who worked on both studies. "But that doesn't mean that if you strip it out and concentrate it in pills, it will have the same benefit, because you've left out important things that go with the fiber."
Among those things are antioxidants, which may delay or slow the damage that oxygen wreaks on cholesterol-damage that makes the cholesterol more likely to clog arteries.
"The bran contains a lot of minerals, and some-like selenium, copper, and manganese are components of antioxidant enzymes," says researcher Lilian Thompson of the University of Toronto.
Those aren't the only antioxidants in whole grains. "Phenolic acids are located in the bran layer," adds Slavin. "And whole grains are concentrated sources of vitamin E and phytic acid."
Diets that are high in wheat bran or other sources of fiber cut the incidence of colon tumors in animals given carcinogens. But in people, some studies see a link between fiber and colon cancer and some don't. To settle the question, the National Cancer Institute (NCI) has launched the Polyp Prevention Trial. It's putting 1,000 people on a low-fat diet that includes 18 grams of fiber a day for every 1,000 calories the participants eat. After four years, the NCI will compare the number of colon polyps (which often become cancerous) in the 1,000 fiber-eaters to the number of polyps in 1,000 people on a typical (low-fiber) North American diet.
But since half of the fiber comes from fruits and vegetables and the other half from grains, the trial is testing not just fiber, but fiber-rich foods.
"It's really a test of a cancer-prevention diet that's low in fat, high in fiber and high in fruits and vegetables," says the NCI's Elaine Lanza. "There are so many phytochemicals, it could take years to sort out which ones matter."
It's also possible that whole grains could prevent other cancers. Toronto's Thompson is especially interested in the phytoestrogens (plant estrogens) and lignans in whole grains.
Some researchers have suggested that lignans and phytoestrogens may take estrogen's place in breast cells, but that they do less damage because they are weak.
But so far, there isn't good evidence that women who consume more fiber from grains have a lower risk of breast cancer.
"And there are no prospective studies where we feed people lignans or phytoestrogens and measure their effect on breast cancer risk," adds Thompson.
"Bread -- it's a great way to go!" That's what Australian researchers in New South Wales called their campaign to boost whole grain bread consumption in a small retirement community.
After four months, sales of whole grain bread rose 58 percent and laxative sales dropped 49 percent in the community where the campaign was carried out (there was no change in a nearby community that had no campaign)."
"The general conclusion is that bran or fiber is beneficial for preventing constipation," says Walid Aldoori, a former Harvard researcher who is now at the Whitehall-Robins pharmaceutical company in Toronto.
That's also true for diverticulosis, which occurs when pockets form in the large intestine. Experts estimate that in North America, a third of people over 45 and two-thirds of those over 85 have it. The vast majority have no symptoms, but others experience constipation, diarrhea, flatulence, pain, bleeding, or inflammation (diverticulitis).
In 1994, Aldoori and co-workers examined the fiber intakes of nearly 48,000
male health professionals. The men who consumed an average of 32 grams of fiber
a day were 42 percent less likely to report symptoms of diverticular disease
than the men who averaged 13 grams a day.
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