Healthful diets not only help prevent cancer; they also improve survival when cancer has been diagnosed. In the last issue of Good Medicine, we looked at how foods affect survival in prostate cancer. In this issue, we look at breast cancer.
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.2 And, 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 thinner women.
Reduced Fat Intake
Those who got more than 5 mg of beta-carotene per day had double the likelihood of survival, compared to women who got less than 2 mg.
Specific dietary factors appear to play key roles in cancer survival. First, two studies of women diagnosed with breast cancer showed that those who had been consuming 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.3,4 One of these studies identified benefits among premenopausal women; 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, N.Y., 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.5 Note that this does not mean a person’s risk of dying is 40 percent. It means that, if the diet contained 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 to 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.6-9 Some studies have failed to confirm the dangers of fatty diets.10-13 However, most evidence indicates that women consuming less fat tend to do better after diagnosis.
Why should a low fat intake improve survival? For starters, 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 tend to have less estrogen coursing through their veins, independent of the difference in their body weight. They may also have stronger immune defenses that can help them fight cancer cells.
Increased Vegetables and Fruits
Some evidence suggests that women whose diets are richer in vegetables and fruits tend to survive longer.2,14 In a study of 103 women in Australia 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.15
Genrerally speaking, women who have been eating fewer fatty foods, more fiber, and more vegetables and fruits at the time of diagnosis live longer and are less likely to have a recurrence.
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.15 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.16
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 as well as 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.15
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.8 The benefit was dose related, meaning the more of these helpful nutrients they got, the better they did. Those who got more than 5 mg of beta-carotene per day had double the likelihood of survival, compared to women who got less than 2 mg. To see what this means on your plate, there are about 5 mg of beta-carotene in ½ a medium carrot or ¼ 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 about 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 80.8
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 to 20 percent increased risk of treatment failure.7
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.16 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.
Combined Diet Effects
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, 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.17
Putting Diet Changes to the Test
The findings described above were generally made by studying the diets of women at the time they were diagnosed with cancer. Generally speaking, women who have been eating fewer fatty foods, more fiber, and more vegetables and fruits at the time of diagnosis live longer and are less likely to have a recurrence. However, it has not yet been proven that changing to a low-fat diet that is loaded with fruits and vegetables after diagnosis will put the brakes on cancer as effectively as having habitually followed such a diet since long before the disease occurred. Studies are now underway to test exactly that.
The Women’s Intervention Nutrition Study (WINS) tests a low-fat diet, deriving 15 percent of calories from fat, in 2,500 postmenopausal women with breast cancer. In the Women’s Healthy Eating and Living (WHEL) study, 3,109 pre- and postmenopausal women with breast cancer will be included in a test of a diet rich in fruits and vegetables. The study’s daily diet guidelines include five vegetable servings, 16 ounces of vegetable juice, three fruit servings, 30 grams of dietary fiber, and no more than 15-20 percent of calories from fat.2,18
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