In 2006, results from of the world largest low fat diet project were published (see reference at end). This was a US government-funded study of 48, 835 postmenopausal women in a multicenter prospective, randomized clinical trial known as the Women’s Health Initiative Randomized Controlled Dietary Modification Trial. The study was conducted from 1993 to 2005 at 40 centers around the country. The volunteers were arbitrarily assigned to either a low-fat diet group (19, 541 women) or a regular diet group (29, 294 women). This large and costly study didn’t find any important differences in breast cancer incidence between postmenopausal women who were invited to eat a low-fat diet and the people who continued to eat their regular diet after about eight years of follow-up. The results did suggest that changing to a low-fat diet may reduce the risk of breast cancer among women who had diets very high in fat to begin with, on the other hand.
Not many women met the 20% fat intake goal. This ‘low-fat diet’ regimen may not have truly been low in fat. Since most women didn’t meet the fat-reduction goal, this study may have proven only that the approach to the statement didn’t work. It didn’t demonstrate that a truly low-fat diet does not help protect you from breast cancer. Getting only 20 percent of your calories from fat is very hard to do. This means that, if you eat 2, 000 calories per day, only 400 calories could come from fat. So it is not surprising that less than a one-third share of the women met this goal after the initial year, and only 14% continued to meet the goal after six years. Because so few women met the needs of the study, it means that we do not really know how a diet low in fat affects breast cancer risk.
We are now learning that HRT isn’t always suitable for long-term use, as it increases risks of breast cancer, stroke and heart disease (Women’s Health Initiative-WHI study). New clinical guidance recommend that GPs offer HRT in only the worst cases and during a period of only five years. 4 out of 5 women find that HRT does not agree with them, even in the early days of use.
Diets were self-reported and infrequent. This may make them unreliable. This study relied on the women’s written reports of what they ate. This may not be an accurate reflection of true intake. These reports were done occasionally. No daily food log or journal was done and checked. Most of us are not proud to admit in an exclusive interview or questionnaire that we have broken the regulations and have not stuck to the ‘prescribed diet. ‘ So there may be a tendency to under-report the number of fat actually eaten.
Other changes besides the low-fat diet. The study didn’t separate out the impact of reducing the number of fat eaten vs. the effects of increasing fruit and vegetable servings. Women in the low-fat diet group ate almost two more servings per day of fruits and vegetables than females in the regular diet group and about one more serving of grains.
Two studies presented during the symposium on human health effects of fruits and vegetables found that the incorporation of vegetable juice in people’s diets was a successful strategy to help them reach the vegetable guidelines (at least 4 servings per day), for example.
Length of follow-up time. While 48, 835 women is a bunch of people, eight years is not a great deal of follow-up time. Eating a low-fat diet for 15 or 20 years may offer more significant benefits and show a stronger relationship between dietary fat and breast cancer risk.
Baseline body mass index. In this study, 74% of females were classified as overweight by body mass index in the early part of the study. So we do not really know if a low-fat diet would offer benefits to women who’re at a normal weight to begin with.
All the women were postmenopausal. It may be that dietary fat plays a greater role in the diets of younger, premenopausal women. It makes sense that your diet during the first 50 years of your life might affect your cancer risk in the latter half of your life. This study does not address that question.
Staying fit is important to your well being. Inactivity is one of those things that is becoming increasingly common in our society. Studies have shown that drinking excessive alcohol, bad eating habits, inactivity, and smoking will all contribute to taking years off of your life. Avoiding those four things makes for a good lifestyle, and a good lifestyle usually affords an active, mobile and, most importantly, a happy life. Everyone has a different level of exercise, that’s why it is not important to make it a priority.
The type of fat wasn’t specified. There are three basic types of fats: saturated, mono-unsaturated, and poly-unsaturated. In this study, women were asked only to reduce fat. They were not asked to look at the various types of fat or told that reducing saturated fats may offer more health benefits than reducing unsaturated fats. Saturated fats are only found in foods that come from animals and are the types of fats that raise your blood cholesterol level. Trans fats (also called trans-saturated fats) are man-made fats. (Vegetable oils are modified to form margarine and vegetable shortening, both of which are trans fats.) Trans fats also are added to prepackaged foods. Saturated fats raise your blood’s ‘bad’ cholesterol (low-density lipoprotein or LDL) level and lower your ‘good’ cholesterol (high-density lipoprotein or HDL) level. Mono-unsaturated and poly-unsaturated fats are present in plant foods like vegetables, nuts, and grains, as well as oils made from these nuts and grains (canola, corn, soybean). Omega-3 and omega-6 fatty acids are poly-unsaturated. Besides vegetables, nuts, and grains, omega-3 and omega-6 fatty acids are likewise found in coldwater fish such as tuna, mackerel, and salmon. Some studies have demonstrated that eating foods that have mono-or poly-unsaturated fats can help reduce your levels of ‘bad cholesterol. ‘ Mono-and polyunsaturated fats may also keep your triglyceride levels low. Triglycerides are a type of fat in your bloodstream.
None of the women in either group were asked to modify their health-related behaviors, such as exercise, smoking, or drinking. These known risk factors for breast cancer were left uncontrolled and may obscure any benefit from eating less fat.
This study is about a low fat diet; it isn’t about going from an overweight/obese state to a normal weight. Eating less fat while staying persistently fat may not help anyone! Since this study cost nearly half a billion dollars, it is not likely that another lifestyle intervention clinical trial at this large scale would be made again anytime soon, particularly in the current US economy.
Reference: Prentice RL, et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women’s Health Initiative Randomized Controlled Dietary Modification Trial. Journal of the American Medical Association, volume 295, pages 629-42, 2006.