Tuesday, January 6, 2015

Health Benefits of Fiber: Cancer and Diabetes

Consumption Of Resistant Starch May Protect Against Bowel Cancer

Western diets are typically low in fibre and have been linked with a higher incidence of bowel cancer. Even though Australians eat more dietary fibre than many other western countries, bowel cancer is still the second most commonly reported cancer in Australia with 30 new cases diagnosed every day.

Dr David Topping, from CSIRO's Food Futures Flagship, said this is referred to as 'the Australian paradox'.

"We have been trying to find out why Australians aren't showing a reduction in bowel cancer rates and we think the answer is that we don't eat enough resistant starch, which is one of the major components of dietary fibre," Dr Topping said.

Resistant starch is a component of dietary fibre that resists digestion in the small intestine and instead passes through to the bowel where it has positive effects on bowel health. Resistant starch is sometimes called the third type of dietary fibre (in addition to soluble and insoluble fibre) and is found in legumes, some wholegrain breads and cereals, firm bananas and cooked and cooled potatoes, pasta and rice.

These findings, published in the April, 2012 issue of The Journal of Nutrition, reinforce the fact that dietary fibre is beneficial for human health, but go further to show that fibre rich in resistant starch is even better.

"It's not just the amount of fibre that we eat that's important, but the diversity of fibre in our diet," Dr Topping said.

"We studied various sources of resistant starch, including corn and wheat, and the results suggest they could all protect against DNA damage in the colon, which is what can cause cancer."

Dr Trevor Lockett, colorectal cancer researcher with CSIRO's Preventative Health Flagship, said Australia has one of the highest incidence rates of bowel cancer in the world.

"Research suggests that improving our diets could go a long way to reducing our personal risk of developing this disease, which would also have the follow-on benefit of reducing healthcare costs associated with bowel cancer.

"These new studies suggest that increasing the amount of resistant starch in our diets may be one important step along the path to reducing the burden of bowel cancer. It takes about 15 years from the time of the first bowel cancer-initiating DNA damage to the development of full-blown bowel cancer, so the earlier we improve our diets the better," Dr Lockett said.

The recommended intake of resistant starch is around 20 grams a day, which is almost four times greater than a typical western diet provides. Twenty grams is equivalent to eating three cups of cooked lentils.

"Currently, it is difficult for Australians to get this much from a typical diet," Dr Topping said.

"We have already had success in developing barley with high levels of resistant starch, and now our focus is on increasing the levels of resistant starch in commonly consumed grains like wheat. These grains could then be used in breads and cereals to make it easier for Australians to get enough resistant starch from their diet."

High Fiber Diet Prevents Prostate Cancer Progression, Study Shows

A high-fiber diet may have the clinical potential to control the progression of prostate cancer in patients diagnosed in early stages of the disease.

The rate of prostate cancer occurrence in Asian cultures is similar to the rate in Western cultures, but in the West, prostate cancer tends to progress, whereas in Asian cultures it does not. Why? A University of Colorado Cancer Center study published in the January 2013 issue of the journal Cancer Prevention Research shows that the answer may be a high-fiber diet.

The study compared mice fed with of inositol hexaphosphate (IP6), a major component of high-fiber diets, to control mice that were not. Then the study used MRI to monitor the progression of prostate cancer in these models.

"The study's results were really rather profound. We saw dramatically reduced tumor volumes, primarily due to the anti-angiogenic effects of IP6," says Komal Raina, PhD, research instructor at the Skaggs School of Pharmacy and Pharmaceutical Sciences, working in the lab of CU Cancer Center investigator and School of Pharmacy faculty member, Rajesh Agarwal, PhD.

Basically, feeding with the active ingredient of a high-fiber diet kept prostate tumors from making the new blood vessels they needed to supply themselves with energy. Without this energy, prostate cancer couldn't grow. Likewise, treatment with IP6 slowed the rate at which prostate cancers metabolized glucose.

Possible mechanisms for the effect of IP6 against metabolism include a reduction in a protein called GLUT-4, which is instrumental in transporting glucose.

"Researchers have long been looking for genetic variations between Asian and Western peoples that could explain the difference in prostate cancer progression rates, but now it seems as if the difference may not be genetic but dietary. Asian cultures get IP6 whereas Western cultures generally do not," Raina says.

How fiber prevents diabetes and obesity 

Most sweet fruit and many vegetables such as salsify, cabbage or beans, as well as
berries and other fresh fruit, vegetables, whole grains, seeds and nuts are rich in so-called fermentable fibers. Such fibers cannot be digested directly by the intestine but are instead fermented by intestinal bacteria into short-chain fatty acids such as propionate and butyrate, which can in fact be assimilated by our bodies. The protective effect of these fibers is well known to researchers: animals fed a fiber-rich diet become less fat and are less likely to develop diabetes than animals fed a fiber-free diet.

Whilw scientists have known for the past twenty years that a fiber-rich diet protects the organism against obesity and diabetes but the mechanisms involved have so far eluded them. A French-Swedish team including researchers from CNRS, Inserm and the Université Claude Bernard Lyon 1 (Unité Inserm 855 “Nutrition et Cerveau”) has succeeded in elucidating this mechanism, which involves the intestinal flora and the ability of the intestine to produce glucose between meals. These results, published in the journal Cell on 9 January 2014, also clarify the role of the intestine and its associated microorganisms in maintaining glycaemia. They will give rise to new dietary recommendations to prevent diabetes and obesity.

Higher intake of cereal fiber associated with reduced diabetes risk

Consuming a healthy diet was associated with reduced risk for type 2 diabetes among women in all racial and ethnic groups but conferred an even greater benefit for Asian, Hispanic, and black women, according to a new study by researchers at Harvard T.H. Chan School of Public Health and Brigham and Women's Hospital.

"This study suggests that a healthy overall diet can play a vital role in preventing type 2 diabetes, particularly in minority women who have elevated risks of the disease. As the incidence of type 2 diabetes continues to increase at an alarming rate worldwide, these findings can have global importance for what may be the largest public health threat of this century," said lead author Jinnie Rhee, who conducted the research as a doctoral student in the Departments of Epidemiology and Nutrition at Harvard Chan and is currently a postdoctoral fellow in the Division of Nephrology at Stanford University School of Medicine.

The study appears online January 15, 2015 in Diabetes Care.

It's estimated that about 29.1 million people in the U.S. and 47 million around the world have diabetes. The World Health Organization projects that diabetes will be the seventh leading cause of death in 2030. The disease, which is often related to excess body weight and physical inactivity, is more common in African Americans, Latinos, Native Americans, and Asian Americans/Pacific Islanders, and the aged. Previous studies have shown links between diet and risk of type 2 diabetes, but most have been conducted in predominately white populations.

The researchers analyzed data on diet in 156,030 non-Hispanic white women and 2,026 Asian, 2,053 Hispanic, and 2,307 black women in the Nurses' Health Study and Nurses' Health Study II. They adjusted for a variety of factors, such as age, physical activity, smoking, family history of diabetes, alcohol intake, postmenopausal status, menopausal hormone or oral contraceptive use, total caloric intake, and body mass index. The women were followed for up to 28 years and filled out diet questionnaires every four years.

The researchers created a dietary diabetes risk reduction score that included components associated with type 2 diabetes risk. A higher score indicated a healthier overall diet--one with lower intake of saturated and trans fats, sugar-sweetened beverages, and red and processed meats; lower glycemic index foods; and higher intakes of cereal fiber, polyunsaturated fats, coffee, and nuts.

Results showed a protective association of similar magnitude between a healthy overall diet and type 2 diabetes risk in all racial and ethnic groups. Comparing the highest to the lowest quartile of dietary diabetes risk reduction score, healthy diet was associated with a 48% lower risk of diabetes in white, 42% in Asian, 55% in Hispanic, and 32% in black women. When all the minority women were combined into one group, those in the highest quartile of dietary score had a 36% lower risk of diabetes compared with women in the lowest quartile. However, because minority women were initially at higher risk of diabetes than white women, in terms of the actual number of avoidable cases, a healthier diet had greater benefit for minority women. The analysis showed that 5.3 cases of diabetes can be prevented per 1,000 white women per year with a healthier overall diet compared with 8.0 cases that can be prevented per 1,000 minority women per year.

Among the findings was that in both white and minority women, higher glycemic index foods as well as each serving of sugar-sweetened beverages, and red and processed meats were associated with increased risk of diabetes. In contrast, higher intake of cereal fiber (grams/day) and each cup of coffee per day were associated with reduced diabetes risk in both groups.

"This finding confirms that we are all in the same boat when it comes to preventing type 2 diabetes by diet. Our next challenge is to put this knowledge into practice so everyone can benefit," said Walter Willett, Fredrick John Stare Professor of Epidemiology and Nutrition and chair, Department of Nutrition at Harvard Chan.

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