Veggies and Cancer Survival

By Wendy Gordon

Extrapolation is a universal human tendency. It's so tempting to take a discrete nugget of information and apply it to a broader, more complex issue. For instance, fruits and vegetables contain antioxidants. Antioxidants prevent cellular changes that can lead to cancer. Therefore fruits and vegetables should help prevent cancer, right?

Unfortunately, a multi-institutional controlled trial (published this June in the Journal of the American Medical Association) illustrates that things are not that simple. In this study, 3,018 women, all of whom had completed treatment for early stage breast cancer, were divided into two groups. The intervention group received intensive dietary counseling designed to dramatically increase their fruit and vegetable consumption, while the control group was simply provided with print materials containing "5 a day" guidelines. The study followed the women for six years, assessing their dietary intake at regular intervals. The counseling worked. The intervention group changed their eating habits dramatically: a 65% increase in vegetable intake; a 25% increase in fruit intake; a 30% increase in fiber; and a 13% decrease in fat. Yet despite all this earnest effort, breast cancer recurrence rates (16%) and mortality rates (10%) remained virtually identical to the control group.

This study wasn't funded by an agribusiness or pharmaceutical corporation. This was a meticulously designed study with variables such as stage of the disease and baseline diet well accounted for. The participants were highly motivated to make dietary changes and respond honestly to investigators. Only 2% dropped out voluntarily over the six year period. The validity of the participant's dietary recalls was reconfirmed by testing plasma biocarotenoid concentration, a marker of fruit and vegetable intake (73% higher in the intervention group).

The results also put into question two other popular truisms of breast cancer treatment. Since some cancers are estrogen-responsive, a lower fat intake (and lower weight) are believed to protect against cancer recurrence. But in this study a significantly lower fat intake showed no effect on recurrence. Those eating a relatively high amount of fat (28.7-33.4%) had identical mortality rates to those eating the least fat (under 23.8%). Women with the highest BMI's (over 30) actually had the lowest risks of cancer recurrence.

In addition, researchers found no "in group differences for depression, social support or quality of life." This contradicts the popular assumption that a positive attitude can help prevent cancerous changes in cells. The results concur with a study published in the May issue of the Psychological Bulletin, which showed no correlation between psychotherapy and cancer survival.

The harsh fact is that cancer is an extremely complex disease. While our understanding of malignant cell changes has expanded considerably, there are still many aspects we do not fully understand.

An important limitation of this study is that it only concerned women who had already developed cancer. Maybe they were genetically susceptible to cancer and/or their cell damage from environmental factors such as diet was already irreversible. This study does not rule out the distinct possibility that a diet high in fruit and vegetables, and lower in fat, may help PREVENT cancer. Research on this possibility is promising, but inconclusive. Studies of the general population have a lot more variables, and participants are less motivated to make changes or report their intake accurately.

Fruits and vegetables provide many health benefits regardless of their role in cancer prevention. They are a source of many valuable vitamins, minerals and phytochemicals, as well as an excellent source of fiber. They also, when prepared well, taste delicious and provide attractive color and texture to meals.

Everyone, regardless of their health status, ought to eat more fruits and vegetables. Generally speaking, cutting down on fat is also beneficial, though building evidence shows that the type of fat one eats is more important than the total amount. And of course, it's healthful to attain and maintain an optimum weight. However, it's worth noting that the cancer patients in this study, at the start of the trial, were already eating an average of 680 kcal/day less than recommended for their age, activity and body size. Cancer patients tend to be underweight; maintaining weight is a bigger challenge than losing it.

A health crisis prompts many people to pay more attention to their bodies, which often involves changes in diet and exercise habits. Generally speaking, this is a positive thing. Yet we need to keep the potential benefits of these changes in perspective, and keep the emphasis on treating the body well rather than creating guilt-driven restrictions.