DDW: To Prevent Colorectal Cancer, a Vegetarian Diet From Day One

WASHINGTON, May 21 -- A vegetarian diet from birth is protective against colorectal cancer, according to a study of lifelong vegetarians in India.

Lifelong vegetarianism, practiced by most Hindus in India, was associated with a 30% risk reduction for colorectal cancer compared with non-vegetarian Indians, reported Yogesh M. Shastri, M.D., of the J.W. Goethe University Hospital in Frankfurt, Germany, at Digestive Disease Week sessions here.

Previous large, well-designed studies, including the NIH-sponsored Women's Health Initiative, failed to show that a diet rich in fruits and vegetables protected against colorectal cancer, Dr. Shastri said. However, these studies included mostly western, middle-aged patients who had adopted vegetarianism later in life.

The current study prospectively analyzed a cohort of about 10,000 Indians seen at a cancer hospital for various types of carcinomas during 2000 to 2005. All patients underwent a nutritional evaluation. There were 2,092 vegetarians.

Hindu vegetarians in India strictly avoid meat, fish, and eggs, although they do consume milk and milk products, Dr. Shastri said.

The researchers estimated the association between vegetarianism and colorectal cancer by case-control analysis. The case group was nearly 800 patients with colorectal cancer. The control group included nearly 2,000 patients with tobacco-related cancers and more than 7,000 patients with other types of cancers.

Multivariate analysis by logistic regression found an inverse association between colorectal cancer and vegetarianism (odds ratio=0.71; 95% confidence interval=0.59 to 0.85).

"This study proves that lifelong vegetarianism prevents colorectal cancer," Dr. Shastri said.

The reason that adopting vegetarianism later in life may not protect against colorectal cancer is that the genetic changes that set the malignant process in motion most likely occur during the first or second decade of life, Dr. Shastri said.

Usually, these changes begin with a deletion of the tumor-suppressing APC gene in colon cells. In the absence of this gene, an adenoma can develop by the fourth or fifth decade and proceed to carcinoma a decade or two later, he said.

Switching to a vegetarian diet or one high in fruits and vegetables may have other health benefits, but doing so by ages 30 or 40 or even as teenagers "is perhaps too late to prevent colorectal cancer," Dr. Shastri said. "There is no shortcut. It has to be from birth."

However, in families with a history of colorectal cancer, having children on a vegetarian diet including milk from birth "could be of great help" in reducing colorectal cancer risk, he added.

The health risks of this approach include deficiencies in protein and vitamin B-12. However, soy products are a good alternative source of protein, and B-12 supplements can be used if necessary. Milk is also a good source of both protein and B-12. "Milk is a complete food except for iron and vitamin C," he said.

Further research should be done to determine which aspects of the Indian vegetarian diet are responsible for the beneficial effect, Dr. Shastri said. Two promising candidates are garlic and the Indian spice curcumin, both of which have been shown to have a chemoprotective effect, he said.