There is little doubt that two articles and an editorial just published in JAMA about the lack of benefit of a low fat diet in reducing the risk of breast and colorectal cancer in post-menopausal women are going to make big news.
The media is already in a frenzy, ready to trumpet the information that watching your diet, if you are a post menopausal woman, doesn’t make any difference in the chance that you will get breast or colorectal cancer.
On the other hand there are a lot of people active in the cancer prevention, epidemiologic, and nutrition communities among others, who are afraid that the message the study appears to send will derail years of efforts to get people more involved in their diets and their lifestyles as they relate to the prevention of disease.
And there are some who are wondering how we ended up with a study that has been about 15 years in the making, involved almost 50,000 women, and didn’t give us a definitive answer to a very important question.
I still recall back in the very early 1990’s, as I attended a number of medical meetings and heard the presentations from the researchers who were going to initiate a massive, government funded study of 50,000 women.
They were planning on studying hormone replacement therapy as the main objective, but there were other issues on the table as well. The effect of diet was on the agenda, and I specifically recall wondering to myself (and occasionally asking the question of the experts in public) did they really think they were going to be able to get women to commit to this study and change their habits?
My experience in my primary care practice was not much different from many colleagues at that time. It was just plain difficult to get people to stick to dietary interventions and maintain them for any length of time. Rare was the person—man or woman—who made the commitment to change their diet, and stick with it long enough to make a difference.
It turned out the recruitment for the study was reasonably successful, and thousands of women were enrolled. Many of us were anxious to hear the results, especially whether the interventions worked as planned. Now we all have an opportunity to examine what has been the largest undertaking of its type and measure its impact and its success.
You may recall hearing about this study before. It is the same study that several years ago led to the conclusion that routine, almost unrestricted use of hormone replacement therapy (HRT) in post-menopausal women caused more harm than good. This report resulted in recommendations that women should stop their HRT because of the risks of continuing the treatment.
The gynecologists who cared for these women didn’t quite see it that way, and their experience suggested that there were some women who still needed HRT.
Patterns of practice and the way hormones were prescribed did change. But not until there were a number of questions raised about the fact that the average age of the women on the study was north of 60 years old—not exactly the type of woman you would want to start on hormones in the first place if she didn’t require them previously.
The result was that in a number of meetings I attended with my gynecologist wife I heard critic after critic claim that, for this reason among others, the study was not applicable to standard practice. The experts called into question the value of the study in terms of assessing the risks and benefits of HRT for the usual woman.
So what did the current studies about the role of low fat diets in reducing the risks of breast and colorectal cancer find?
There were actually two reports on cancer (and a third on heart disease, but I will leave that to others to discuss).
The women who participated in the study were randomly assigned to continue a regular diet, or begin a program to reduce their dietary fat intake to 20% of their daily calorie intake, increase their intake of fruits and vegetables, and eat more servings of grains on a daily basis. Reducing food intake and losing weight were not goals of the study.
The women in the “control” group did not have any further discussions or meetings about their diets, while the women in the intervention group were counseled on a regular basis and encouraged to maintain their dietary intervention program over the course of the study.
The women who were advised about their diet did in fact lower their fat intake, but not as much as the researchers had hoped. And they did increase their fruit, vegetable and grain intakes, although the degree of success varied over the time of the study.
The results of having a group of women commit to a low fat diet program was that, after being followed for an average of about 8 years, there was no detectable difference in the risk of getting colorectal cancer or breast cancer.
(It should be noted that in the breast cancer group the data suggest that perhaps with additional follow-up over time there may be a benefit of the low fat diet in reducing the risk of breast cancer. But as of right now, the researchers could not conclude with certainty that there is a real difference present.)
The women in the study group had lost a small amount of weight compared to the control group. But, as the authors noted, weight loss was not the goal of the study.
Now let’s ask the obvious question: if you took a group of women where about 12,000 out of about 19,000 in the study group were age 60 and over (up to age 79), and you put them on a low fat diet, would you expect to see an effect in either breast or colorectal cancer incidence? Would you expect them to adhere for a long time to a diet that was very low in fat content?
And, if you followed these women for about 8 years, knowing that colorectal cancer in the usual case takes about 10 years to develop from a polyp to a cancer and probably starts well before that time, would you expect to see a benefit?
The same questions can be asked about breast cancer, which is a disease that increases with age, but probably starts many years before it is detected by mammography.
That’s the problem we face in interpreting this study and assessing its implications and its impact.
My colleagues here at the American Cancer Society have made the point to me that we have not been enamored of the theory that fact intake is related to either breast or colorectal cancer for some time. And there has been some question as to whether fruits and vegetables make a difference in breast cancer.
These were questions when the study was conceived, but research over time has indicated that they are probably not a primary factor in the development of the diseases under study.
We have been fans of advising women to maintain a healthy body weight, and exercising regularly, both of which are associated with decreased rates of colorectal and breast cancer. There is nothing in this study that goes against these recommendations.
And, in a study published in 2003 in the New England Journal of Medicine, researchers from the American Cancer Society clearly pointed out the relationship between obesity and a number of cancers, including breast and colorectal cancer.
So, what we knew then and what we know now has changed. It is important that we keep this perspective in mind as we evaluate these reports.
The current study, according to my colleagues and I suspect others as well, is not going to have us change our guidelines or our public guidance on this subject. And there may be criticisms that for reasons beyond the investigators’ control the group that was studied may have been too old to have derived any benefit from the low fat diet.
There is, unfortunately, the potential that there may be some unintended harm that comes from this report, namely that women may abandon a healthy diet and the need to maintain a healthy body weight as part of a comprehensive cancer (and other disease) prevention program.
If that occurs, and if that is the message the media carries, then a well done, well intentioned, well written scientific report may result in some unfortunate consequences.
Hopefully, we won’t end up with misunderstandings about some very important recommendations about what we need to do to reduce the risk and burden of cancer in ourselves and in our communities.
So, you are not off the hook. Following a healthy diet, getting regular exercise and maintaining a healthy weight are still the rule of the day.
Sorry about that (Well, maybe not so sorry).