Low-Fat Diets and the Risk of Breast Cancer, Colorectal Cancer and Cardiovascular Disease in Women: Beyond the Negative Headlines

The first few months of 2006 saw week after week of seemingly negative or unimpressive results of large trials in a number of areas championed by many alternative health care practitioners and "liberal" allopathic doctors. Things began with the apparent failure of a low-fat diet to reduce cancer and heart disease in women,^1-3 and then progressed to negative reports on calcium and vitamin D,^4,5 glucosamine and chondroitin,⁶ saw palmetto,⁷ homocysteine,^8,9 and vitamins C and E.¹⁰

In the May 8, 2006 issue of Dynamic Chiropractic, I went beyond the headlines of a major glucosamine and chondroitin study. This month, let's again look past the headlines, which recently have proclaimed the failure of low-fat diets in reducing the risk of breast cancer, colorectal cancer and cardiovascular disease in women.

Information Is Not Bad

Studies that one labeled as "bad" by groups disappointed in the outcome still contain a wealth of information. In a given study, when we know the amount, type, form or duration that a given substance is prescribed or a habit change is implemented, we can then analyze the ability to increase, decrease, resolve or promote a given result, response or effect in the species, race, gender or age group studied. If we know the specifics of how the information from a study is obtained, we can apply it in proper context. Information gets the "bad" tag when, in actuality, it is simply misleading due to an incomplete presentation in the press, which may be caused by a number of reasons.

For example, the vast majority of journalists do not read the entire scientific paper they are reporting on. Rather, they base their conclusion on the paper's abstract or a press release. Of the few who do read the entire article, many lack the training to interpret scholarly publications properly. Finally, headlines often exclude the basic data (described above) that is required for the layperson (who has neither the time nor the desire to research the topic in depth) to apply the information correctly.

The Women's Health Initiative Randomized Controlled Dietary Modification Trial

Between 1993 and 1998, women at 40 centers across the United States were recruited to participate in a dietary modification trial. The last intervention was held in August 2004, and the statistical analysis was concluded in March of 2005. The mean follow-up time was 8.1 years, with a maximum of 11.2 years. The intervention group contained 19,541 women; in the comparison or control group, there were 29,294 women. Ages of the women ranged from 50 to 79. In general, they were overweight and/or obese. The mean average body weight for both groups was 169 pounds.

In the first year, the dietary intervention group received 18 intensive, small group-counseling sessions to educate them on the reduction of dietary fat and to increase daily servings of fruits, vegetables and whole grains.

Over the next (on average) seven years, the intervention sessions were held every three months (four times per year). There were a total of 46 meetings with certified nutritionists trained in the prioritizing of the study, including the top goal of reducing the percentage of dietary fat calories to 20 percent.

Diets were monitored by food frequency questionnaires.

All participants completed a questionnaire at baseline and after the first year. On a rotating basis, one-third of each group then completed a food frequency questionnaire each year. Thus, each participant completed two more food frequency questionnaires over a six-year period. All of the women also had a medical questionnaire update every six months throughout the intervention period. Mammographies were performed every two years, and electrocardiograms were performed every three years. The participants' personal physicians monitored the colorectal examinations.

Headlines and Sound Bites

The following are quotations from the conclusions in the abstracts of the referenced papers:

• "Among postmenopausal women, a low-fat dietary pattern did not result in a statistically significant reduction in invasive breast cancer risk over an 8.1 year average follow-up period."¹
• "In this study, a low-fat dietary pattern intervention did not reduce the risk of colorectal cancer in postmenopausal women during 8.1 years of follow-up."²
• "Over a mean of 8.1 years, a dietary intervention that reduced total fat intake and increased intakes of vegetables, fruits, and grains did not significantly reduce the risk of CHD, stroke, [or] CVD in postmenopausal women."³

Headlines such as those above cause the average person to think, "Forget the chicken breast; I'll have a cheeseburger!" But, ask any nutritionist or dietitian if having 29 percent of your diet's calories come from fat is a "low-fat dietary pattern." Most of them would say no. Ask if their idea of "increased intakes of vegetables and fruits" is one additional serving per day, and you will get the same answer.

In defense of the authors,^1-3 their initial definition of a low-fat diet was 20 percent. Unfortunately, even in the first year (meeting with nutritionists 18 times), subjects were only able to reduce daily fat intake to 24.3 percent. When the sessions were reduced to quarterly appointments in subsequent years, fat intake increased to almost 30 percent - only 8 percent below what participants ate prior to the study.

A More Accurate Sound Bite

When older (ages 50-79), overweight women consumed an extra serving of fruits and vegetables, increased their fiber intake by 2 grams and lowered dietary fat intake from 38 percent to 29 percent of their calories, the risk of colorectal cancer, breast cancer, and heart disease was, at best, only slightly reduced over an eight-year period.

A More Accurate Headline

A diet of 30 percent fat did not reduce the risk of cancer or heart disease in women.

Conclusion

The information provided by these studies showed that after an average of eight years, the participants: 1) reduced their fat intake from 37.8 percent to 28.8 percent of their energy; 2) increased their servings of fruits and vegetables from 3.6 to 4.9; and 3) increased their fiber intake from 15.4 grams to 16.9 grams per day. This caused a non-statistically significant reduction in total cancers (10.37 percent to 9.96 percent), cardiovascular disease (7.13 percent to 6.94 percent) and mortality (4.96 percent to 4.86 percent).

We did learn that it is very difficult for overweight, middle-aged females to reduce their dietary fat intake in free-living situations, even with extensive nutritional counseling. It remains to be seen how conversion to a true low-fat dietary pattern would affect the risk factors for overweight women in this age group over an 8 to 10-year period.

References

1. Prentice RL, Caan B, Chlebowski RT, et al. Low-fat dietary pattern and risk of invasive breast cancer: The Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA 2006;295:629-642.
2. Beresford SAA, Johnson KC, Ritenbaugh NL, et al. Low-fat dietary pattern and risk of colorectal cancer: The Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA 2006;295:643-654.
3. Howard BV, Van Horn L, Hsia J, et al. Low-fat dietary pattern and risk of cardiovascular disease: The Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA 2006;295:655-666.
4. Jackson RD, La Croix AZ, Gass M, et al. Calcium plus vitamin D supplementation and the risk of fractures. NEJM 2006;354:669-683.
5. Wende-Wactawski J, Kotchen JM, Anderson GL, et al. Calcium plus vitamin D supplementation and the risk of colorectal cancer. NEJM 2006;354:684-696.
6. Clegg DO, Reda DJ, Harris CL, et al. Glucosamine, chondroitin sulfate, and the two in combination for painful knee osteoarthritis. NEJM 2006;354:795-808.
7. Bent S, Kane C, Shinohara K, et al. Saw palmetto for benign prostatic hyperplasia. NEJM 2006;354:557-566.
8. Lonn E, Yusuf S, Arnold MJO, et al. Homocysteine lowering with folic acid and B vitamins in vascular disease. NEJM 2006;354:1567-1577.
9. Bonaa KH, Njolstad I, Ueland PM, et al. Homocysteine lowering and cardiovascular events after acute myocardial infarction. NEJM 2006;354:1578-1588.
10. Rumbold AR, Crowther CA, Haslam RR, et al. Vitamins C and E and the risks of preeclampsia and perinatal complications. NEJM 2006;354:1796-1806.