Susan Dudley, PhD and Jacqueline Britz, Cancer Prevention and Treatment Fund
The Women’s Health Initiative (WHI) began in 1992 as a long term national health research effort focused on disease prevention among postmenopausal women. Over 161,000 women have participated in this research, which has provided information that has saved lives of women across the country. The original study, lasting 15 years, was aimed at finding evidence-based strategies for prevention of many health conditions, including heart disease, breast and colorectal cancer, and fracture in postmenopausal women. The WHI Extension Study, carried out from 2005 to 2010, followed up with 115,400 participants from the original study to gather more data and answer additional questions.
Many experts were disappointed when a 2006 dietary trial that was part of the original WHI study showed that a low-fat diet did not reduce women’s risks of heart attacks, strokes, breast cancer, or colon cancer. Since then, other studies have come out, including subsequent diet trials with women enrolled in the WHI. The results have been inconsistent: some positive and some negative.
So, what’s a woman to eat? Is there, in fact, a right combination of fats, carbohydrates, proteins, and other nutrients? Studying and understanding the effects of diet and changes to diet is always complicated. Consider the following:
- Any time we limit our intake of one type or category of food, we tend to fill the gap by eating more of another type of food. In the WHI, women were not encouraged to cut calories or lose weight.
- Our bodies have an astonishingly efficient “thermostat” that works hard all our lives to return us to whatever body weight and body composition it has been set at, based on what has been normal for us over the long-term. That is why keeping weight off after just about any kind of crash diet is so hard to do.
The Women’s Health Initiative: Diet Trials
The main goal of the initial WHI dietary trial was to determine whether low-fat diets could reduce the risk of developing breast cancer, colon cancer, stoke, and heart disease.
The 19,541 women participating in the low-fat diet trial were divided into two groups: one group was encouraged to continue eating as they always had, while study participants in the other group were encouraged (through participation in a series of training sessions) to modify their diets by reducing fat and increasing their consumption of fruits, vegetables, and grains. By later comparing the rates of health problems, including breast and colon cancer and cardiovascular disease, between the two groups of women, scientists hoped to see whether the training sessions would work and whether the low-fat diet would improve women’s health.
The results, reported in 2006, were not encouraging, since few differences emerged in the health status of the women in the two groups. However, there were a number of weaknesses in the investigation that made the results difficult to interpret. Two are especially important:
- All dietary fat is not alike. For example, we now know that saturated fats and trans-fats can have particularly negative health effects and that certain fats-like those found in walnuts or some fish oils-can actually be beneficial. However, the trial did not attempt to influence which types of fats the women were eating.
- The women who were in the group that was trained to improve their diet didn’t improve their diet as dramatically as the researchers hoped. The “low-fat” group for this study averaged 29% calories from fat instead of the targeted 20%. The 29% finding is not much different from the average adult in the U.S. who gets 32.7% or more of his or her calories from fat. The study participants’ reported consumption of fruits and vegetables was only slightly raised, and their consumption of grains did not change. It’s impossible to know if there would have been a bigger difference in the incidence of cancer, stroke, and cardiovascular disease in the two groups if the “low-fat” group had improved their eating habits more dramatically.
When the researchers studied the women in the diet modification group whose total fat intake was reduced the most, they found that they didsignificantly lower their risk for invasive breast cancer. And those who consumed less saturated fat and ate more fruits and vegetables reduced their blood pressure, cholesterol and other problems that may eventually reduce their risk of heart attack, stroke, and heart disease.
Results from More Recent Studies
Since the publication of the initial results in 2006, subsequent diet trials with women enrolled in the WHI have shown a mix of positive and discouraging results. Below are descriptions of four additional trials. While these studies also have limitations, their findings have implications for disease prevention among women.
Low-Fat dietary pattern and Cancer incidence (2007):
The same group of women from the original WHI study was followed for 8 years for a trial that investigated low fat dietary patterns and their effect on cancer incidence. Despite the discouraging results from the first published investigation on the effects of a low-fat diet, this study found lower rates of ovarian cancer among the group of women who followed a low-fat diet. For every 100,000 participants on a modified low-fat diet per year, there were 36 cases of ovarian cancer diagnosed, compared to 43 cases of ovarian cancer among the women who did not modify their diet. This difference in ovarian cancer rates between the two groups was statistically significant, meaning that it was unlikely to have happened by chance. So, while a low-fat diet was not associated with a reduced risk of breast cancer, colorectal cancer, or cardiovascular disease, it was associated with a lower risk of ovarian cancer.
Low-Fat dietary pattern and risk of treated Diabetes Mellitus in postmenopausal women (2008):
The same participants from the original 2006 trial were also subjects of an 8 year long investigation looking at the relationship between a low-fat diet and diabetes. Just as was true in the initial trial, the group of women following a low-fat diet did not appear to have substantial health gains over the group of women who did not follow the low-fat diet. The participants with a modified diet had only a 4% reduced risk of developing diabetes as compared with the participants in the usual diet group. While that may not seem very impressive, the participants in the low-fat diet group maintained a lower weight, on average, than participants in the usual diet group. The researchers noted that the participants with the biggest reduction of fat in their diets did have a lower diabetes risk that was statistically significant. Based on this study, they concluded that losing weight is more important for reducing one’s chances for developing diabetes than the quantity of fat, carbohydrates or other nutrients consumed. The women in the study who followed a low-fat diet were more likely to maintain a lower weight and, therefore, indirectly may have a reduced their risk of diabetes.
Calcium/Vitamin D supplementation may help prevent weight gain in postmenopausal women (2007):
A large portion of the participants from the initial 2006 trial were used for another study published in 2007 to determine the influence of calcium and vitamin D on weight gain. Research suggests that these two nutrients may be able to initiate the decline of fat cells, reduce the generation of new fat cells, and consequently decrease the amount of weight gain. For 7 years, researchers monitored a group of women taking pills with active calcium plus vitamin D, and others taking placebos. The women taking pills with active calcium plus vitamin D gained on average about a quarter of a pound less than women in the placebo group. Although this tiny difference was statistically significant, it isn’t a meaningful difference. More important, the women in this first group were less likely to gain weight at all during the trial. The women who benefited the most were those who, prior to the start of the study, consumed less than the recommended 1,200 mgs per day of calcium (this is the amount recommended for women in the age range of 50-79). Therefore, while taking active calcium and vitamin D may help women maintain their weight, its benefits are likely to be more substantial in women who lack sufficient calcium and vitamin D.
Multivitamin use and risk of Cancer and Cardiovascular Disease (2009):
Finally, a 2009 study used data collected from all participants in the Women’s Health Initiative throughout the hormone trials, observational study, and dietary study (a total of 161,808 participants). Study enrollment took place between 1993 and 2008, with follow up conducted through 2005. Data were collected for a median of 8 years in the clinical trials and 7.9 years in the observational study. Participants using multivitamins (41.5%) were compared to participants not taking multivitamins to see which group had higher rates of breast, colorectal, endometrial, renal, bladder, stomach, lung, and ovarian cancer. Researchers were also interested in seeing if there was a difference between the two groups in terms of cardiovascular events such as stroke or heart attack. The women who took a daily multivitamin were no less likely to develop or die from cancer or cardiovascular disease than the women who did not take a multivitamin.
What We Have Learned from These Studies
Don’t let the negative headlines of some of these studies fool you. Although these studies provide conflicting results, with only some supporting the relationship between certain diets and disease prevention, and others proving inconclusive, the studies taken altogether still provide a lot of important information:
- Women whose fat intake was lowered the most had better health outcomes.
- The women in the WHI were not encouraged to reduce their calories. That may have been a mistake. Research now clearly shows that being overweight increases the risk of breast cancer, heart disease, arthritis, and many other diseases, so more targeted dietary modifications that include emphasis on achieving and maintaining healthy body weight might be more effective.
- Even when evidence does not conclusively show that a particular kind of diet, such as low-fat, can prevent or reduce the risk of disease, the dietary change may still improve health by lowering or controlling weight. Excess weight and obesity increase the risk for many diseases and cancer.
- There is no way to know whether the dietary intervention in this study would have been more effective if it had been started earlier in the women’s lives-when the women were in their 20’s, 30’s, or 40s, rather than at 50-79 years of age.
- We know that many cancers and other health conditions take 15-20 years to develop and usually show up among older individuals. We still don’t know what impact dietary modifications will have on the women’s health 10 years after the study’s end.
- One of the most important messages is that dietary changes are easier to talk about than to do something about. The participants in the dietary modification groups probably started out with very good intentions about following the recommended diet, but that turned out to be impossible for many of them. Whether this is because of pressure to join the family for dessert, the endless temptation created by advertisements for foods that were not compatible with the diet, or other causes, it is important for us to take such real-world obstacles into account. It doesn’t make sense to measure the effectiveness of dietary change by focusing on women in a “diet modification group” if the women didn’t substantially modify their diet. It makes more sense to study the women who succeeded in modifying their diet compared to those who didn’t. Those are the women whose health tended to benefit most.
Maintaining moderation and balance
So, given the findings of these various studies, are there changes in our diet that we should make? Even though the results are mixed, it’s clear that most people will benefit from a well-balanced diet that is low in sodium, added sugars, and saturated- and trans-fats, and a diet that is high in fresh fruits, vegetables, whole grains, and heart-healthy unsaturated fats, with moderate amounts of dairy products and meat protein. The USDA Dietary Guidelines for Americans gives specific recommendations for dietary intake, suggesting that women should strive to consume between 1.5 and 2 cups of fruit each day, between 2 and 2.5 cups of vegetables, and 3 cups of low fat milk products. Women should eat approximately 6 oz. of grains each day (with a minimum of 3 oz. coming from whole grains), and between 5 and 5.5 oz. of meat/beans. “Good” fats, found in fatty types of fish (i.e. salmon, herring, sardines), plant oils like extra-virgin olive oil, avocados, seeds, and nuts, are also an essential part of a healthy diet and have been found to help prevent incidence of disease.
General guidelines for healthy eating may need to be modified to accommodate specific health problems or disease risks. For example, people with high cholesterol may need to reduce the amount of fat and food they consume each day that comes from animals (red meats, eggs, and dairy products). Helpful nutritional guidelines are available at: http://www.mypyramid.gov/index.html.
Also, do not forget to watch calories, because excess weight can cause or complicate so many health problems. Reaching and maintaining a healthy body weight is important. In order to lose weight, it is important to make sure that a person burns more calories than he or she consumes. As a result it is essential to find a healthy balance between food consumption and physical activity.
Remember that serving size and portion size are not the same thing. Serving size is a standardized quantity of food that we use to measure nutrients.Portion size is the amount we pile on our plates. Keep in mind that one serving of cooked vegetables is usually about one-half cup (about a hand-full!) and a serving of meat is about the size of a deck of cards. This means that most people can fit in all those recommended servings of fruits and vegetables every day while still reducing their total calorie intake and losing weight. But it also means that the portions you serve yourself may be much higher in calories than the standard serving size would be.
And don’t forget that beverages have calories too! Try to limit your intake of high calorie or sugary drinks, as well as alcoholic drinks. They should be consumed in moderation, or not at all. It is recommended that women limit alcoholic intake to a maximum of one drink per day (i.e. 12 fl. oz. beer, 5 fl. oz. wine, or 1.5 fl. oz. 80-proof distilled spirits). More resources regarding a healthy diet for women can be found at http://womenshealth.gov/FitnessNutrition/eatinghealthy/.
Lastly, women over 50 may want to take calcium and vitamin D supplements. There appears to be little risk in taking them and many potential benefits, including help in maintaining weight-particularly if their diet and indoor lifestyles are causing them to have low levels of these essential nutrients.
- The original reports of the WHI findings on low-fat diet can be found in the Journal of the American Medical Association, February 8, 2006 – Vol 295, No. 6, pages 629, 643, and 655.
- This report, in addition to the other reports cited in this article, can be accessed online through the Women’s Health Initiative website: http://www.nhlbi.nih.gov/whi/index.html.
- Dietary Guidelines for Americans [Current Guidelines – 2005 Dietary Guidelines]. (n.d.). Retrieved from USDA Center for Nutrition Policy and Promotion website: http://www.cnpp.usda.gov/DGAs2005Guidelines.htm
- Vitamin D [Dietary Supplement Fact Sheet]. (n.d.). Retrieved from National Institutes of Health – Office of Dietary Supplements website: http://ods.od.nih.gov/factsheets/VitaminD-QuickFacts/
- Calcium [Dietary Supplement Fact Sheet]. (n.d.). Retrieved from National Institutes of Health – Office of Dietary Supplements website: http://ods.od.nih.gov/factsheets/Calcium-Consumer/