Healthful diets not only help prevent cancer, evidence suggests that they also improve survival when cancer has been diagnosed. The first clues that foods might affect the course of breast cancer came from studies of women in Japan in the early 1960s. Compared to Western women, Japanese women were much less likely to develop the disease and much more likely to survive it if it occurred.1 Over the next several decades, researchers have followed up on these observations to try to clarify what is the best diet for cancer survival. Although this work is still in its early stages, important information has already come to light.
One of the best-established factors affecting breast cancer survival is body weight. Women with breast cancer who are near their ideal body weight at the time of diagnosis are more likely to survive than are women with higher body weights. In a 2002 review of twenty-six studies published since 1990 on body weight and cancer recurrence or decreased survival in women previously diagnosed with breast cancer, seventeen studies showed that higher body weight was associated with increased risk; seven studies showed no relationship; and two showed an inverse relationship between body weight and risk.2 Overall, the body of evidence supports a relationship between higher body weights and poor outcomes.
Compared to Western women, Japanese women were much less likely to develop breast cancer and much more likely to survive it if it occurred.
The relationship may hold even among relatively thin women. A 2006 study from Shanghai, China, studied the relationship between body mass index (BMI) and survival in 1,455 women aged twenty-five to sixty-four who had previously been diagnosed with breast cancer.3 For reference, a healthy BMI is between 18.5 and 24.9 kg/m2. Women with a BMI below 23 had a five-year survival rate of 86.5 percent. Those who were slightly heavier, with a BMI of 23.00–24.99, had a slightly lower five-year survival rate of 83.8 percent. Those with a BMI of 25 or greater had a five-year survival of 80.1 percent.
Although weight gain often occurs after diagnosis, studies suggest that women who avoid weight gain after diagnosis tend to have longer, disease-free survival.2
The link between lower body weight and better survival may relate to estrogens, female sex hormones that can encourage the growth of cancer cells. In essence, body fat acts like an estrogen factory, producing estrogens from other compounds coming from the adrenal glands (small organs situated atop each kidney). As a result, women with more body fat tend to have higher amounts of estrogens circulating in their blood compared to leaner women.
Specific dietary factors appear to play key roles in cancer survival. First, two studies of women diagnosed with breast cancer showed that those who consumed less fat prior to diagnosis generally had smaller tumors with less evidence of cancer spread compared to women whose diets had included more fatty foods.4,5 One of these studies identified benefits among premenopausal women and the other among postmenopausal women.
Studies that have followed women for several years after diagnosis have generally found that those with less fatty diets prior to diagnosis live longer than other women. In one of the first such studies, researchers at the State University of New York in Buffalo found that women with advanced cancer had a 40 percent increased risk of dying at any point in time for every 1,000 grams of fat they consumed per month.6 Note that this does not mean a person’s risk of dying is 40 percent. It means that if a person’s diet contains an extra 1,000 grams of fat per month at the time of diagnosis, that person’s risk of dying is 40 percent higher than it would otherwise have been. There is, of course, tremendous variation from one woman to another, so this figure is simply an overall observation drawn from the group of participants. To make this more concrete, the difference between a typical American diet and a low-fat vegan diet is approximately 1,000–1,500 grams of fat per month, which corresponds to a 40–60 percent difference in mortality risk at any point in time.
Other studies found much the same thing—fatty diets are associated with increased risk, and that is particularly true for saturated fat, the kind that is common in meat, dairy products, eggs, and chocolate.7-10 Some studies have failed to confirm the dangers of fatty diets.11-14 However, most evidence indicates that women consuming less fat tend to do better after diagnosis, including the Women’s Intervention Nutrition Study (WINS), sponsored by the National Cancer Institute (NCI).15 This study followed nearly 2,500 postmenopausal women with breast cancer for five years after their standard surgery and cancer treatments. Researchers instructed some of them to continue their regular diets while the rest were put on a low-fat diet. The women continuing their usual diets consumed an average of 51.3 grams of fat per day, which is still lower than the average American’s fat, while the low-fat group averaged 33.3 grams per day—slightly more than in a typical vegetarian diet. After five years, 12.4 percent of the women eating their usual diet had cancer recurrences compared to only 9.8 percent of the low-fat diet group, a 24 percent reduction in recurrence.
Why does low fat intake improve survival? To begin with, low-fat diets tend to be modest in calories, since fats and oils are the densest source of calories of any food we consume. In fact, some investigators believe that the main problem with fatty diets is simply their high calorie content. In addition, women who eat less fat and more fiber tend to have less estrogen (independent of the difference in their body weight). They may also have stronger immune defenses that can help them fight cancer cells.
Evidence suggests that diet changes must be substantial to be effective. The Women’s Health Initiative included 48,835 participants, aged fifty to seventy-nine, who were free of breast cancer, and tested a diet that emphasized vegetables, fruits, and grains.16 Fat intake fell from 38 percent of calories at the beginning of the study to 24 percent at one year, but slipped back up to 29 percent at six years. After 8.1 years of follow-up, overall breast cancer risk fell 9 percent, but the difference was not statistically significant, meaning that it could have occurred due to chance. However, risk of one type of breast cancer—progesterone receptor-negative tumors—fell by 24 percent. While the study was not a survival study—it assessed the risk of cancer developing in the first place, rather than the course of the disease after diagnosis—it suggests that modest dietary changes may bring only modest results.
Fiber is essential to the body’s ability to eliminate excess estrogens. As the liver filters estrogens from the blood, it sends them through the bile duct into the intestinal tract, where fiber soaks them up and carries them out of the body. A study in Sweden found that women with higher fiber intake at the time of breast cancer diagnosis were more likely to have smaller tumors compared to women with lower fiber intake.17 The amount consumed was not particularly high. Those women with larger tumors (greater than 20 millimeters) averaged 16 grams of fiber per day compared to 19 grams for women with smaller tumors. Most authorities recommend fiber intake of at least 30 grams daily, and an optimal intake is probably over 40 grams.
Some evidence suggests that women whose diets are richer in vegetables and fruits tend to survive longer.2,18 In a study of 103 women in Australia, who were followed for six years after they were diagnosed with breast cancer, those who consumed the most fruits and vegetables rich in beta-carotene or vitamin C had the best chance for survival. The researchers divided the group into thirds based on how much beta-carotene they got each day in the foods they chose. It turned out that in the group getting the least beta-carotene, there were twelve deaths over the next six years. In the middle group, there were eight deaths; and in the high-beta-carotene group, there was only one death.19
In the digestive tract, beta-carotene is converted to vitamin A. In turn, vitamin A is converted to a compound called retinoic acid, which has a demonstrable anticancer effect on cells in test-tube studies.16 A Swedish study found much the same thing: Among women with breast cancer, those consuming more vitamin A were more likely to have estrogen receptor-rich tumors, a good prognostic sign.17
The Australian researchers also analyzed their data in another way, looking simply at how much fruit of any kind the women had been eating, including both beta-carotene-rich fruits and other varieties, such as apples, bananas, berries, grapes, and dried fruits. The same sort of pattern emerged. In the group eating the least fruit, there were twelve deaths; in the middle group, there were six deaths; and in the group consuming the most fruit, there were only three deaths.19
Similarly, a study of Canadian women with breast cancer found that those getting the most beta-carotene and vitamin C had significantly better survival odds.9 The benefit was dose related, meaning the more of these helpful nutrients they got, the better they did. Those who got more than 5 milligrams of beta-carotene per day had double the likelihood of survival compared to women who got less than 2 milligrams. To understand what this means on your plate, there are about 5 milligrams of beta-carotene in half a medium carrot or one-fourth cup of cooked sweet potato.
For vitamin C, those getting more than 200 milligrams each day had roughly double the survival odds compared to those getting less than 100 milligrams per day. In practical terms, an orange has about 60 milligrams of vitamin C, and a one-cup serving of broccoli or other green vegetables has about 80.9
Vitamin E may have the opposite effect. In one study, women with breast cancer consuming larger amounts of vitamin E had poorer survival. Every one-milligram increase in daily vitamin E intake was associated with approximately a 15–20 percent increased risk of treatment failure.8
These dietary factors tend to work together: A diet that is higher in fruits and vegetables will also tend to be high in fiber and low in fat. In turn, women who eat such diets tend to be slimmer than other women, thus avoiding the risks of overweight. One study suggested that there may be a measurable benefit of these combined effects. Researchers at Mt. Sinai Medical Center in New York found that women with breast cancer who were slimmer tended to live longer, and those who had lower cholesterol levels also lived longer. But the women at greatest risk of dying were those who were overweight and had high cholesterol levels.20
The Women’s Healthy Eating and Living (WHEL) Study included more than 3,000 pre- and postmenopausal women previously treated for breast cancer in a test of two different diets rich in fruits and vegetables.21 Half the participants (the intervention group) were asked to include in their daily diets five vegetable servings, 2 cups of vegetable juice, three fruit servings, 30 grams of dietary fiber, and no more than 15–20 percent of calories from fat. A comparison group was asked to consume at least five fruit and vegetable servings per day.
In 291 of the study participants, changes in diet and hormone function were compared between the two diet groups.22 The women who ate less fat and more fiber found that the amount of estrogen in their blood fell to safer levels, confirming that diet changes really do help get hormones into better balance.
In the same study, the investigators tracked the experience of 1,551 women assigned to the comparison group, using blood tests for plasma carotenoids as an indicator of vegetable and fruit intake.23 As in any large group, their diets varied from one person to another. It turned out that those with the highest carotenoid concentrations—indicating high vegetable and fruit intake—had a 43 percent lower risk of either cancer recurrence or a new primary breast cancer compared to women with lower blood levels of carotenoids.
After approximately seven years of follow-up, those women in the comparison group who followed the guideline of eating at least five fruit and vegetable servings daily and who were also physically active had an almost 50 percent reduction in mortality compared to women who did not meet these healthful guidelines.24 However, the recommendations for even greater vegetable and fruit intake made for the intervention group did not extend benefits beyond those achieved by the five-a-day (comparison) group.25
While the WHEL participants succeeded at emphasizing vegetable and fruit intake, they did not maintain a low fat intake or a high fiber intake. The intervention group did reduce fat intake to 21 percent of calories in the first six months, but fat intake gradually climbed back to 29 percent by the six-year point. Similarly, fiber intake was only slightly higher at six years (24 grams per day) compared to the study’s onset (21 grams). As a result, neither the intervention nor the comparison group succeeded at weight loss; both groups were overweight at the beginning of the study and gained a small amount of weight as the study progressed. A vegetarian or vegan regimen may have been a better choice; the meat and dairy products that were permitted in the WHEL guidelines contain significant amounts of fat and contribute no fiber.
Nonetheless, the WHEL study demonstrated that women previously treated for breast cancer who consume at least five vegetable and fruit servings daily and are physically active have a large measure of protection (nearly 50 percent reduction in mortality), and their protection is not increased by pushing vegetable intake even higher. The study did not test other potentially helpful dietary measures.
Exercise may also improve breast cancer survival. A study published in the Journal of the American Medical Association concluded that physical activity after breast cancer diagnosis may reduce a woman’s risk of death from the disease. In this study, the greatest benefit was shown in women who exercised the equivalent of walking at an average pace for three to five hours per week.26
Broccoli or Cauliflower with Sesame Salt