[PHNUTR-L] Diet and cancer prevention: New evidence for the protective effects of fruits and veggies

[Kathrynne Holden]

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Public release date: 6-Dec-2007
http://www.eurekalert.org/pub_releases/2007-12/aafc-dac112807.php

Contact: Greg Lester
greg.lester at aacr.org
267-646-0554
American Association for Cancer Research

Diet and cancer prevention: New evidence for the protective effects of 
fruits and veggies

PHILADELPHIA -- The age-old refrain, “Eat your vegetables!” gets 
scientific support as researchers present the latest findings on cancer 
prevention at the American Association for Cancer Research’s Sixth 
Annual International Conference on Frontiers in Cancer Prevention, being 
held December 5 – 8 in Philadelphia, Pennsylvania.

Today, researchers present new data that demonstrate how diets full of 
raw vegetables --particularly broccoli sprouts -- and black raspberries 
could prevent or slow the growth of some common forms of cancer.

Dietary administration of black raspberries modulates markers of 
oxidative stress in patients with Barrett’s esophagus. Abstract no. B34

Black raspberries may protect against esophageal cancer by reducing 
oxidative stress in patients with Barrett’s esophagus (BE), a 
pre-cancerous condition that usually arises due to gastroesophageal 
reflux disease, report researchers at The Ohio State University.

According to the researchers, BE patients have a 30- to 40-fold 
increased risk of developing esophageal adenocarcinoma (EAC), the 
fastest growing cancer in terms of incidence in the United States. EAC 
is a deadly cancer with a 15 percent five-year survival rate; an 
estimated 14,000 people will die from esophageal cancer in the U.S. in 
2007. Moreover, a number of treatment options are available to BE 
patients for symptom relief, researchers say, but none has proven 
curative or eliminated the risk of cancer progression.

“In addition to gastroesophageal reflux disease, increasing body mass 
index or body fatness is strongly associated with EAC development; 
whereas, plant-based diets and particularly increased fruit consumption 
has been associated with decreased risk for EAC,” said Laura A. Kresty, 
Ph.D., assistant professor of at Ohio State University.

According to Kresty, research using animal models of BE showed that 
black raspberries inhibited chemically induced oral, esophageal and 
colon cancers. The studies showed that berries reduced measures of 
oxidative stress (the destruction done to cells by oxygen ions or small 
reactive molecules containing oxygen), decreased DNA damage, inhibited 
cellular proliferation rates, and reduced the number of pre-cancerous 
cells in the esophagus and colon.

“We can give black raspberries before we have any initiated cells, or we 
can administer after we already know we have initiated cells,” Kresty 
said. “What’s promising about the berries is that they work in both 
cases, and in multiple models. There aren’t nearly as many agents that 
work in the latter scenario.”

In this study, BE patients ate 32 or 45 grams (female and male, 
respectively) of freeze-dried black raspberries daily for 26 weeks. 
After 26 weeks, patients experienced a statistically significantly 
decline in the mean urinary levels of 8-Isoprostane, an indicator of 
global oxidative stress and DNA damage -- both processes linked to the 
development of BE and EAC. According to Kresty, 58 percent of patients 
experienced marked individual level declines of 8-Isoprostane. Among 37 
percent of BE patients, the black raspberry regimen also resulted in the 
increased expression of tissue levels of GSTpi. GSTpi is an enzyme that 
detoxifies carcinogens and reactive oxidants and is typically reduced in 
Barrett’s epithelium compared to normal esophageal epithelium.

“Black raspberries have a good profile in terms of tolerability -- many 
of the potential toxic side effects associated with a new drug are less 
of an issue because we are simply administering a food in a 
non-traditional manner,” Kresty said. “Patients seem amenable to such an 
approach, they understand it and enjoy being able take positive action 
for potential health gains.”

Inhibition of urinary bladder carcinogenesis by broccoli sprouts. 
Abstract no. B149:

Your mom was right when she told you to eat your broccoli, or at least 
your broccoli sprouts. Researchers have found that this rich source of 
isothiocyanates (ITCs) – a well-known class of cancer prevention agents 
-- could play a direct role in preventing bladder cancer.

“The bladder is like a storage bag, and cancers in the bladder occurs 
almost entirely along the inner surface, the epithelium, that faces the 
urine, presumably because this tissue is assaulted all the time by 
noxious materials in the urine,” said senior author Yuesheng Zhang, 
M.D., Ph.D, professor of oncology at Roswell Park Cancer Institute. “The 
ITCs in broccoli sprout extracts after oral ingestion are selectively 
delivered to the bladder epithelium through urine excretion.”

Using a rat model of bladder cancer, Zhang and his colleagues found that 
freeze-dried aqueous extract of broccoli sprouts significantly, and 
dose-dependently, inhibited bladder cancer development. The incidence, 
multiplicity, size and progression of bladder cancer were all inhibited 
by the extract, while the extract itself caused no observable changes in 
the bladder. This protective effect of the extracts was associated with 
a significant increase in the bladder of several enzymes that are known 
to protect against oxidants and carcinogens, Zhang says.

In the body, ITCs are metabolized to dithiocarbamates (DTCs). The 
researchers measured the levels of ITCs and DTCs in the blood, tissue 
and urine of the rats fed with the extracts. More than 70 percent of the 
ITCs present in the extracts were excreted into the urine as ITC 
equivalents (ITCs + DTCs) in 12 hours after a single oral dose, 
indicating high bioavailability and rapid urinary excretion.

What is more striking, Zhang says, is that the concentrations of ITC 
equivalents in the urine of extracts-treated rats were two to three 
orders of magnitude higher than those in plasma, indicating that the 
bladder epithelium is most exposed to orally dosed ITCs. Indeed, tissue 
levels of ITC equivalents in the bladder were significantly higher than 
in the liver, demonstrating that the ITCs in the extracts are 
efficiently and selectively delivered to the bladder epithelium through 
urinary excretion, Zhang concludes.

Consumption of raw, but not cooked, cruciferous vegetables and reduction 
of bladder cancer risk. Abstract no. B47:

While researchers have long known that cruciferous vegetables are chock 
full of isothiocyanates (ITCs), which are a well-known class of cancer 
prevention agents especially promising in bladder cancer 
chemoprevention, they didn’t know how much one needed to eat to reap the 
protective benefits.

Researchers from Roswell Park Cancer Institute report that three or more 
servings a month of raw cruciferous vegetables like broccoli, cabbage 
and cauliflower, may reduce bladder cancer risk by approximately 40 
percent, overall.

The Roswell Park team surveyed the dietary habits of 275 individuals 
with incident, primary bladder cancer and 825 individuals without 
cancer. The researchers surveyed patients about their pre-diagnostic 
intake of raw and cooked cruciferous vegetables, their smoking habits 
and other cancer risk factors. They observed a strong and statistically 
significant inverse association between bladder cancer risk and raw 
cruciferous vegetable consumption. When compared to smokers who ate less 
than three servings of raw vegetables, non-smokers who ate at least 
three servings a month were almost 73 percent less likely to develop 
bladder cancer, the researchers say.

A key factor in the research was that it’s a survey of raw cruciferous 
vegetables. Previous research had surveyed intake of any cruciferous 
vegetables – cooked or not – and results proved inconsistent. Cooking 
significantly reduces the availability of ITCs for absorption into the 
body, according to researchers.

“Cooking can reduce 60 to 90 percent of ITCs,” says Li Tang, M.D., Ph.D. 
of Roswell Park Cancer Institute and lead researcher on this study. 
“Heating destroys the enzyme that converts the precursor glucosinolates 
into ITCs, and also destroys ITCs already formed, which is why you need 
to eat raw cruciferous vegetables to receive the food’s maximum benefit.”
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
"Ask the Parkinson Dietitian"  http://www.parkinson.org/
"Eat well, stay well with Parkinson's disease"
"Parkinson's disease: Guidelines for Medical Nutrition Therapy"
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