Specific Plants Protect Against Specific, Not All, Cancers

Pam Harrison

August 29, 2012

August 29, 2012 (Montreal, Quebec) — Not all fruits and vegetables protect against cancer; rather, specific plants — mostly vegetables — protect against specific cancers, according to research presented here at the Union for International Cancer Control World Cancer Congress 2012.

An unhealthy diet — a key promoter of certain cancers — is always associated with fruit and vegetable deficiency, noted Richard Beliveau, PhD, from the University of Montreal, University of Quebec at Montreal, and McGill University in Quebec. Fruit and vegetable deficiency, in turn, is associated with the formation of a carcinogenic environment, he added.

"Plants do not produce chemicals to help us fight cancer; essentially, plants produce an arsenal of toxic chemicals that kill yeast, bacteria, and insects. Out of this huge chemodiversity, research has shown that some of these chemicals have potent anticancer properties," he explained.

However, these anticancer properties are associated with specific fruits and vegetables, not all of them," Dr. Beliveau reported.

Probably the best example of a phytochemical that serves as an antiinflammatory is curcumin. "Turmeric is the most potent source of curcumin, and curcumin is the most potent antiinflammatory phytochemical we know," Dr. Beliveau told Medscape Medical News.

These antiinflammatory properties could prevent cancer from developing, he suggested. It is widely recognized that an inflammatory stimulus created by diseases, such as inflammatory bowel disease, is a major risk factor for colorectal cancer. Similarly, infection with Helicobacter pylori can lead to chronic gastritis and, in some cases, gastric cancer.

The diet-derived phytochemical epigallocatechin gallate, found in green tea, targets tumor invasion and metastasis, as well as angiogenesis. Resveratrol from grapes has been found to possess strong proapoptotic activity against cells isolated from a variety of tumors; this activity correlates with the inhibition of tumor growth in animals. Broccoli has sulforaphane, which kills cancer cells directly, Dr. Beliveau noted.

There is robust evidence that specific phytochemicals targeting carcinogenic pathways lead to significant reductions in specific types of cancer. For example, in prospective studies done with tens of thousands of participants, researchers have linked the consumption of cruciferous vegetables (cauliflower, broccoli, kale) to reductions of approximately 50% in both bladder and prostate cancer, and of about 30% in lung cancer.

Tomato consumption has been associated with a 25% reduction in prostate cancer, and the consumption of leafy green vegetables with generous amounts of dietary folate have been shown to reduce the risk for pancreatic cancer by approximately 75%.

"Just as you don't give vinblastine to treat all cancers, you don't protect against all cancers with the same food," Dr. Beliveau said. "When we look at cancer prevention, we need to look at the type of vegetables that are consumed, not the quantity. If we consume specific foods in combination, rates of protection against cancer should be higher," he noted.

The Other Side of the Cancer Story

The "other side" of the cancer story is obesity. "Every pound of fat necessitates 400 kilometers of blood vessels to feed it, so it produces a lot of VEGF and other growth factors to promote blood vessel development. This creates the perfect environment in which to allow tumor cells to develop."

In fact, what investigators collectively call unhealthy lifestyle practices — obesity, poor diet, and lack of physical activity — account for approximately 35% of all cancers, which is much as smoking, he added.

"Human cancers are monoclonal," Dr. Beliveau explained. "It takes a single tumor cell decades to progress to a mass of billions of cells. So most people over 40 are tumor carriers, but the tumor starts in adolescence.... It is our lifestyle that creates a favorable or unfavorable environment for microtubules to evolve into a clinically relevant cancer," he said.

As an example, Dr. Beliveau noted that the incidence of endometrial cancer is 4 times higher in obese women than in normal-weight women.

Survival is also affected by weight; in prostate cancer, for example, mortality is increased by 50% in men who are overweight and by 150% in men who are obese.

The 5 "golden rules" of chronic disease prevention apply to cancer prevention as well: do not smoke; maintain a normal body mass index (BMI) (for cancer prevention, a BMI of 21 to 23 kg/m² is ideal); eat an abundance of plant products (fruits, vegetables, whole grains); exercise at least 30 minutes a day; and stay away from industrially prepared (junk) food.

Dr. Beliveau added that "cancer survivors should follow the same recommendations for the secondary prevention of cancer. This is the first time this recommendation has been made, so it's important for patients to know."

He is a scientist who can speak to the people.

"One of the great challenges in cancer prevention is public engagement," Jon Kerner, PhD, from the Canadian Partnership Against Cancer, told Medscape Medical News. "We need more scientists who know the science but who are able to articulate what it means to the public in everyday language.... The great thing about Dr. Beliveau...is that he is a scientist who can speak to the people."

Union for International Cancer Control (UICC) World Cancer Congress 2012. Presented August 28, 2012.

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