Can Changing Your Diet Reduce Your Risk of Breast Cancer?
by Dr. C.H. Weaver M.D. 5/2020
Many “anti-cancer” diets have been proposed but none have been clinically demonstrated to actually reduce the risk of developing cancer. An unhealthy weight has long been known to increase the risk of chronic conditions such as diabetes and heart disease, and there is increasing evidence that being overweight increases the risk of developing certain types of cancer and can decrease the survival of individuals with cancer.
Some but not all studies have suggested that women who consume a low-fat diet have both a reduced risk of developing breast cancer and are more likely to survive after they overcome breast cancer. (1,4,5) The Women's Health Initiative trial was designed to evaluate dietary modification for breast cancer prevention and was initiated in 1993. The study was designed to evaluate whether a low-fat dietary intervention in postmenopausal women with no prior history of breast cancer could reduce the risk of developing breast cancer. The study evaluated an intervention of reduced fat intake in women who had no breast cancer history and had no suspicious findings of breast cancer on screening mammography prior to entry.
The Women’s Health Initiative trial enrolled 48,835 postmenopausal women, ages 50 to 79 between 1993 and 1998. who were randomly assigned to a low-fat diet. About 19,600 women were part of the low-fat diet group, which recommended reducing fat intake to 20% of daily caloric intake and increased vegetable and fruit intake to five servings a day and grains to six servings a day and compared that group to a group of women consuming their usual diet. The diet was comparable to the DASH (Dietary Approaches to Stop Hypertension) diet, with slightly more emphasis on dietary fat reduction and gave participants a framework to follow. In the other group, approximately 29,300 women learned about good nutrition and a healthy diet but they did not have to change their eating habits.
When initially evaluated in 2006 the low-fat diet was not found to reduce breast cancer risk. Now after almost 20 years of follow-up, the study shows a significant reduction in breast cancer-related deaths and deaths after breast cancer among women consuming the low-fat diet. The incidence of developing breast cancer was estimated to be about 8% lower in the dietary intervention compared with the comparison group during the trial. The dietary modifications however significantly reduced the actual risk of dying from breast cancer. This is because women in the dietary group were diagnosed with significantly fewer estrogen receptor-positive, progesterone receptor-negative, HER2-negative cancers, which carry a poor prognosis.
- Women on the low-fat diet continued it for 8.5 years significantly reducing dietary fat intake and experienced on average a reduction in weight of about 5 pounds.
- 3,061 women developed invasive breast cancer during an average of 11.4 years of follow-up. Compared to women with stable weight, those who lost weight were 12% less likely to develop breast cancer.
- Women randomly assigned to a low-fat diet also had a significantly reduced risk of death after surviving breast cancer. For the women with breast cancer, the low-fat eating plan decreased their risk of death by 22%.
- Weight loss of greater than 15% was associated with a 37% reduction in breast cancer risk. In other words, the more weight a woman lost, the more likely she was to avoid developing breast cancer.
The takeaway message, perhaps especially for postmenopausal women with early stage breast cancer, is “moderation.” Women in the intervention group reduced their dietary fat intake to about 25% of their calories (not a big change from an average intake of about 32%) and had a weight loss of about 5 pounds. Making moderate adjustments to your diet can have a huge impact.
According to the study authors “physicians can tell postmenopausal women under their care that a dietary change to reduce total fat while increasing vegetables, fruit, and grains can lead to a reduction by about one-fifth in the risk of developing breast cancer and dying from it over a period of 1 to 2 decades, other benefits for those making this dietary change may include reduction in the risk of insulin-requiring diabetes and reduction in coronary heart disease.
Trans Fats Linked to Breast Cancer Risk
Trans fats were developed in the 1900s and are added to foods to extend their shelf-life. A common example of a trans fat is Crisco®, or shortening, which was first developed in 1911. Previous studies have shown that consumption of trans fats may elevate “bad cholesterol” levels, which may lead to an increased risk of coronary heart disease. According to a study conducted in France, high levels of trans fats in the blood contributed to an increased risk of invasive breast cancer.
In the current study, researchers assessed the association between dietary fat intake and breast cancer risk among 19,934 European women. Each woman provided a blood sample and completed a questionnaire regarding her dietary history. During an average of seven years’ follow-up, 363 women were diagnosed with invasive breast cancer. Other women of similar age, menopausal status, and similar blood results who did not develop breast cancer were compared with the women who did develop cancer.
- Results of the study revealed that increasing levels of fatty acids present in blood were associated with an increased risk of breast cancer, specifically among patients found to have high levels of trans fats.
- However, other forms of fats, such as monounsaturated fats, were not found to contribute to breast cancer risk.
Researchers concluded that an increased breast cancer risk was associated with increasing levels of trans fats, which may indicate a high intake of industrially processed foods. Women concerned about reducing their risk of breast cancer through dietary measures may wish to consult their healthcare provider.
What is the DASH Diet? - Healthy eating to lower your blood pressure.
DASH stands for Dietary Approaches to Stop Hypertension and is a lifelong approach to healthy eating that was designed to help treat or prevent high blood pressure (hypertension) that was developed by the National Institutes of Health. The DASH diet encourages individuals to reduce the sodium in their diet and eat a variety of foods rich in nutrients that help lower blood pressure, such as potassium, calcium and magnesium. The DASH diet is also in line with dietary recommendations to prevent osteoporosis, cancer, heart disease, stroke and diabetes.
The DASH diet includes lots of whole grains, fruits, vegetables, and low-fat dairy products. The DASH diet also includes some fish, poultry and legumes, and encourages a small amount of nuts and seeds a few times a week.
The DASH diet is low in saturated fat, trans fat and total fat and individuals can eat red meat, sweets and fats in small amounts. Here's a look at the recommended servings from each food group for the 2,000-calorie-a-day DASH diet.
Grains: 6 to 8 servings a day
Grains include bread, cereal, rice and pasta. Examples of one serving of grains include 1 slice whole-wheat bread, 1 ounce dry cereal, or 1/2 cup cooked cereal, rice or pasta.
· Focus on whole grains because they have more fiber and nutrients than do refined grains. For instance, use brown rice instead of white rice, whole-wheat pasta instead of regular pasta and whole-grain bread instead of white bread. Look for products labeled "100% whole grain" or "100% whole wheat."
· Grains are naturally low in fat. Keep them this way by avoiding butter, cream and cheese sauces.
Vegetables: 4 to 5 servings a day
Tomatoes, carrots, broccoli, sweet potatoes, greens and other vegetables are full of fiber, vitamins, and such minerals as potassium and magnesium. Examples of one serving include 1 cup raw leafy green vegetables or 1/2 cup cut-up raw or cooked vegetables.
· Don't think of vegetables only as side dishes — a hearty blend of vegetables served over brown rice or whole-wheat noodles can serve as the main dish for a meal.
· Fresh and frozen vegetables are both good choices. When buying frozen and canned vegetables, choose those labeled as low sodium or without added salt.
· To increase the number of servings you fit in daily, be creative. In a stir-fry, for instance, cut the amount of meat in half and double up on the vegetables.
Fruits: 4 to 5 servings a day
Many fruits need little preparation to become a healthy part of a meal or snack. Like vegetables, they're packed with fiber, potassium and magnesium and are typically low in fat — coconuts are an exception.
Examples of one serving include one medium fruit, 1/2 cup fresh, frozen or canned fruit, or 4 ounces of juice.
· Have a piece of fruit with meals and one as a snack, then round out your day with a dessert of fresh fruits topped with a dollop of low-fat yogurt.
· Leave on edible peels whenever possible. The peels of apples, pears and most fruits add interesting texture to recipes and contain healthy nutrients and fiber.
· Remember that citrus fruits and juices, such as grapefruit, can interact with certain medications, so check with your doctor or pharmacist to see if they're OK for you.
· If you choose canned fruit or juice, make sure no sugar is added.
Dairy: 2 to 3 servings a day
Milk, yogurt, cheese and other dairy products are major sources of calcium, vitamin D and protein. But the key is to make sure that you choose dairy products that are low-fat or fat-free because otherwise they can be a major source of fat — and most of it is saturated.
Examples of one serving include 1 cup skim or 1 percent milk, 1 cup low-fat yogurt, or 1 1/2 ounces part-skim cheese.
· Low-fat or fat-free frozen yogurt can help you boost the amount of dairy products you eat while offering a sweet treat. Add fruit for a healthy twist.
· If you have trouble digesting dairy products, choose lactose-free products or consider taking an over-the-counter product that contains the enzyme lactase, which can reduce or prevent the symptoms of lactose intolerance.
· Go easy on regular and even fat-free cheeses because they are typically high in sodium.
Lean meat, poultry and fish: 6 one-ounce servings or fewer a day
Meat can be a rich source of protein, B vitamins, iron and zinc. Choose lean varieties and aim for no more than 6 one-ounce servings a day. Cutting back on your meat portion will allow room for more vegetables.
Examples of one serving include 1 egg or 1 ounce of cooked meat, poultry or fish.
· Trim away skin and fat from poultry and meat and then bake, broil, grill or roast instead of frying in fat.
· Eat heart-healthy fish, such as salmon, herring and tuna. These types of fish are high in omega-3 fatty acids, which are healthy for your heart.
Nuts, seeds and legumes: 4 to 5 servings a week
Almonds, sunflower seeds, kidney beans, peas, lentils and other foods in this family are good sources of magnesium, potassium and protein.
They're also full of fiber and phytochemicals, which are plant compounds that may protect against some cancers and cardiovascular disease.
Serving sizes are small and are intended to be consumed only a few times a week because these foods are higher in calories.
Examples of one serving include 1/3 cup nuts, 2 tablespoons seeds or nut butter, or 1/2 cup cooked beans or peas.
· Nuts sometimes get a bad rap because of their fat content, but they contain healthy types of fat — monounsaturated fat and omega-3 fatty acids. Nuts are high in calories, however, so eat them in moderation. Try adding them to stir-fries, salads or cereals.
· Soybean-based products, such as tofu and tempeh, can be a good alternative to meat because they contain all of the amino acids your body needs to make a complete protein, just like meat.
Fats and oils: 2 to 3 servings a day
Fat helps your body absorb essential vitamins and helps your body's immune system. But too much fat increases your risk of heart disease, diabetes and obesity.
The DASH diet strives for a healthy balance by limiting total fat to less than 30 percent of daily calories from fat, with a focus on the healthier monounsaturated fats.
Examples of one serving include 1 teaspoon soft margarine, 1 tablespoon mayonnaise or 2 tablespoons salad dressing.
· Saturated fat and trans fat are the main dietary culprits in increasing your risk of coronary artery disease. DASH helps keep your daily saturated fat to less than 6 percent of your total calories by limiting use of meat, butter, cheese, whole milk, cream and eggs in your diet, along with foods made from lard, solid shortenings, and palm and coconut oils.
· Avoid trans fat, commonly found in such processed foods as crackers, baked goods and fried items.
· Read food labels on margarine and salad dressing so that you can choose foods that are lowest in saturated fat and free of trans fat.
DASH diet: Sodium levels
The DASH diet emphasizes vegetables, fruits and low-fat dairy foods — and moderate amounts of whole grains, fish, poultry and nuts.
In addition to the standard DASH diet, there is also a lower sodium version of the diet. You can choose the version of the diet that meets your health needs:
· Standard DASH diet. You can consume up to 2,300 milligrams (mg) of sodium a day.
· Lower sodium DASH diet. You can consume up to 1,500 mg of sodium a day.
Sweets: 5 servings or fewer a week
You don't have to banish sweets entirely while following the DASH diet — just go easy on them. Examples of one serving include 1 tablespoon sugar, jelly or jam, 1/2 cup sorbet, or 1 cup lemonade.
· When you eat sweets, choose those that are fat-free or low-fat, such as sorbets, fruit ices, jelly beans, hard candy, graham crackers or low-fat cookies.
· Artificial sweeteners such as aspartame (NutraSweet, Equal) and sucralose (Splenda) may help satisfy your sweet tooth while sparing the sugar. But remember that you still must use them sensibly. It's OK to swap a diet cola for a regular cola, but not in place of a more nutritious beverage such as low-fat milk or even plain water.
· Cut back on added sugar, which has no nutritional value but can pack on calories.
DASH diet: Alcohol and caffeine
Drinking too much alcohol can increase blood pressure. The Dietary Guidelines for Americans recommends that men limit alcohol to no more than two drinks a day and women to one or less. The DASH diet doesn't address caffeine consumption. The influence of caffeine on blood pressure remains unclear. But caffeine can cause your blood pressure to rise at least temporarily.
DASH diet and weight loss
While the DASH diet is not a weight-loss program many adherents lose unwanted pounds because it can help guide you toward healthier food choices. The DASH diet generally includes about 2,000 calories a day. If you're trying to lose weight, you may need to eat fewer calories and adjust your serving goals.
Tips to cut back on sodium
The foods at the core of the DASH diet are naturally low in sodium. So just by following the DASH diet, you're likely to reduce your sodium intake. You also reduce sodium further by:
· Using sodium-free spices or flavorings with your food instead of salt
· Not adding salt when cooking rice, pasta or hot cereal
· Rinsing canned foods to remove some of the sodium
· Buying foods labeled "no salt added," "sodium-free," "low sodium" or "very low sodium"
One teaspoon of table salt has 2,325 mg of sodium. When you read food labels, you may be surprised at just how much sodium some processed foods contain.
Even low-fat soups, canned vegetables, ready-to-eat cereals and sliced turkey from the local deli — foods you may have considered healthy — often have lots of sodium.
You may notice a difference in taste when you choose low-sodium food and beverages. If things seem too bland, gradually introduce low-sodium foods and cut back on table salt until you reach your sodium goal. That'll give your palate time to adjust.
Using salt-free seasoning blends or herbs and spices may also ease the transition. It can take several weeks for your taste buds to get used to less salty foods.
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- Chlebowski RT, et al "Dietary modification and breast cancer mortality: long-term follow-up of the Women's Health Initiative randomized trial" J Clin Oncol 2020; DOI: 10.1200/JCO.19.00435.
- Chajes, V., Thiebaut, A., Rotival, M., et al. Association between serum trans monounsaturated fatty acids and breast cancer risk in the E3N-EPIC study. American Journal of Epidemiology [early online publication]. April 4, 2008
- Association of Low-Fat Dietary Pattern With Breast Cancer Overall Survival
- JAMA. 2006;295:629-642.
- Chlebowski R, Blackburn G, Elashoff R, et al. Oral presentation from the 2006 annual San Antonio Breast Cancer Symposium. Mature analysis from the women's intervention nutrition study (WINS) evaluating dietary fat reduction and breast cancer outcome. December 16, 2006. Abstract #32