High-Fat Diets Linked with Breast Cancer

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Harvard Medical School
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High-Fat Diets Linked with Breast Cancer

News Review From Harvard Medical School

April 10, 2014

News Review From Harvard Medical School -- High-Fat Diets Linked with Breast Cancer

Diets high in saturated fat may increase the chance of developing 3 common types of breast cancer, a new study says. The study included more than 337,000 women who answered questions about diet. In the next 11½ years, about 10,000 were diagnosed with breast cancer. Researchers adjusted the numbers to account for other things that can affect breast cancer risk. They found that women whose diets were high in total fat and saturated fat were 30% more likely to develop 2 specific types of breast cancer than women who ate the least fat. These cancers are known as estrogen-receptor (ER) positive and progesterone-receptor (PR) positive. They grow in response to hormones. Women who ate the most saturated fat were also more likely to develop HER2-negative breast cancer. These cancers do not contain the HER2 protein, which promotes cancer growth. Breast cancers can have some or all of these characteristics. In fact, most cancers diagnosed in the United States and Europe are ER- and PR-positive and HER2-negative. So the most common types of breast cancer are linked with high-fat diets. The Journal of the National Cancer Institute published the study. HealthDay News wrote about it April 9.


By Howard LeWine, M.D.
Harvard Medical School


What Is the Doctor's Reaction?

This study once again reopens the question of whether fat in our diets influences breast cancer risk. Prior studies have reached different conclusions. Some show that women who regularly consume a high-fat diet have an increased risk of the disease. Other studies show no link between fat intake and breast cancer.

The link between breast cancer and dietary fat depends on the type of breast cancer, according to this research. And it also depends on what types of fat a woman eats, not just the amount.

Breast cancer samples are now routinely tested for the presence or absence of three tumor markers:

  • Estrogen receptors
  • Progesterone receptors
  • Human epidermal growth factor (HER2) receptors

Tumors that have each type of receptor are called positive for that receptor. Those without it are said to be negative.

Women with breast cancer that is positive for estrogen and progesterone receptors and negative for HER2 generally have a better prognosis. Genetically, these tumors resemble normal breast tissue more closely than breast cancers with different markers.

Breast cancer that is HER2-positive is more likely to grow faster and spread beyond the breast more often. So the prognosis is not as good. The prognosis is even worse if a woman's cancer is negative for all three receptors. This is known as "triple negative" breast cancer.

In this study, eating a diet rich in saturated fats increases the risk of breast cancers that are estrogen and progesterone-positive and HER2-negative. These are the breast cancers that tend to have a better prognosis. But saturated fat did not increase the risk of breast cancers with other receptor patterns.


What Changes Can I Make Now?

For decades, we have been warned of the dangers of saturated fats. Study results such as these add to the concern. However, other recent studies are beginning to question whether the scare has been overstated.

You could just think, "Forget about it. Until the experts figure this out, I'll eat what I want." But let me suggest why I will continue to limit saturated fat and advise my patients, both male and female, to do the same.

Saturated fats may not be as harmful as we previously believed. But there is no evidence that they are good for you. And there is plenty of evidence to remain concerned about links between high saturated fat intake and increased risks of heart disease and some types of cancers, including breast cancer.

Although this study doesn't discuss it, the source of saturated fat might be important. For example, eating lots of red meats and processed meats appears to increase breast cancer risk.

Here are other ways you can help decrease your risk of breast and other types of cancers:

  • Maintain a healthy weight or lose weight, if necessary. In particular, watch your portion sizes and avoiding sugary foods and drinks.
  • Don't smoke or use other tobacco products.
  • Get at least 5 servings of fruits and vegetables daily.
  • Aim for 30 minutes of activity daily. Set a long-term goal of 60 minutes of activity most days.
  • Drink alcohol in moderation, if you drink it at all.


What Can I Expect Looking to the Future?

More and more experts recommend Mediterranean-style eating. The main components are lots of vegetables, fruits, whole grains, healthy fats and non-meat protein sources. It makes sense. It's not a specific diet and therefore offers flexibility.

Based on research done so far, eating Mediterranean-style surely can't hurt, as long as you keep total calories in check. And my bet is it will help keep your heart and the rest of your body healthy.

Last updated April 10, 2014

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