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Exceeding Your 5-a-Day Doesn't Reduce Cancer Risk
Eating double the amount of veggies and fruits recommended by general dietary guidelines doesn't reduce the likelihood of breast cancer recurrence, new research suggests.
For breast cancer survivors who are meeting the '5-a-day' dietary goals set by the National Cancer Institute, there is no benefit to further increasing their vegetable and fibre intake in terms of preventing breast cancer recurrence. That’s according to researchers from Stanford University in the US.
The study documented the effect of diet on over 3000 women previously treated for early-stage breast cancer. Half of the women were assigned to eating five servings of fruits and vegetables daily. The other half were asked to eat almost double that amount, while reducing their fat intake.
After following the women for an average of more than 7 years, the researchers found that the breast cancer recurrence and mortality rates were nearly identical for both groups of women.
"I was really surprised and, frankly, a little disappointed by the results," said medical professor Dr Marcia Stefanick. "We expected the two-fold increase in vegetables and fruits, plus the increased fibre and reduced fat to make a difference in the recurrence rates."
Although the recurrence rates for both groups were the same, Stefanick noted that the rate for both groups was much lower than the norm.
"I would certainly hope that people don't interpret these results as evidence that eating a lot of vegetables doesn't make a difference in breast cancer," she said.
The theory that eating more fruits and vegetables might stave off cancer stems from studies showing that plant-derived foods contain anti-carcinogens. There have also been studies indicating that high-fat diets are linked to an increased risk for cancer.
The study is the largest-ever randomized clinical trial to assess the connection between diet and breast cancer recurrence.
The women assigned to the high-veggie group made enormous changes in their diets, Stefanick said. First, they were asked to limit the amount of fat in their diet to 15-20 percent of their total calories. In addition, they were expected to consume five servings of vegetables and vegetable juice, three servings of fruit and 30 grams of fibre on a daily basis. While that sounds like a lot of veggies, Stefanick pointed out that a serving size amounts to about a half-cup of chopped or shredded vegetables.
But it couldn't be just any vegetable. "We were really strict about what counted as a vegetable," she said. "Iceberg lettuce and white potatoes didn't count. We emphasized nutrient-dense vegetables, such as dark, leafy greens, sweet potatoes and carrots."
The women in the 5-a-day group were asked to follow generally accepted dietary guidelines – eat five daily servings of fruits and vegetables, 20 grams of fibre and get less than 30 percent of their calories from fat.
"Diet alone might not be enough, but it would be interesting to explore the effect of a combined approach," Stefanick said.
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