Do’s & Don’ts of Eating While Taking Tamoxifen

There are some foods you should not eat while taking tamoxifen.  There are other foods that are fine to eat.  And there are some foods that can make your tamoxifen work harder for you.  I am going to tell you some of the do’s and don’ts of eating while taking tamoxifen.

I took tamoxifen for a little over 1.5 years for my ER+ breast cancer.  I didn’t tolerate it well and asked for my oncologist to find another way to prevent my breast cancer from returning.  However, hundreds of thousands of women are alive today because of this drug.  While it has a long list of side effects, tamoxifen can save lives.

Estrogens Promote Growth of Some Breast Cancers

Over 70% of breast cancers respond to the female hormone, estrogen.  The estrogens stimulate the cancer cells to grow and replicate, making tumors bigger and spreading the cancer to other areas of the body.  So, doctors are always trying to reduce a breast cancer patient’s estrogen levels or response to estrogen.  There are a few techniques that oncologists use to do this, but by far tamoxifen is one of the most common.

There are millions of people taking tamoxifen to prevent estrogen responsive breast cancer growth and recurrence.  It is the most widely prescribed hormonal drug for cancer patients on the market. 

What Is Tamoxifen & How Does It Work?

Tamoxifen is a drug classified as a SERM, or selective estrogen receptor modulator.  This means that tamoxifen binds to estrogen receptors and blocks the effects of estrogen on breast cancer cells.  Thus, these cells can’t grow or replicate.  Hence, tamoxifen stops breast cancer from growing and spreading. And it is very successful at doing its job.  Tamoxifen reduces the rate of breast cancer recurrence by 30 – 50% and mortality rates by 25% over 10 – 14 years. 

What Is The CYP Catalytic Cycle?

CYP stands for Cytochrome P.   There are many different liver enzymes that belong to the Cytochrome P450 family. But the one that is most important for people taking tamoxifen is CYP2D6.  This is the enzyme, found in the liver, that breaks down tamoxifen into its active compounds.  People taking tamoxifen that have low CYP2D6 levels seem resistance to tamoxifen and are at a higher risk of cancer recurrence. 

Drugs & Foods Can Affect The CYP Catalytic Cycle

This is important to know because many drugs, supplements and some foods affect the level of CYP2D6 activity in our liver.  There also seems to be a genetic and ethnicity component to the level of this enzyme activity.  I will just be talking about food in this article.  But it is important for you to talk to your oncologist or pharmacist about all the drugs & supplements you are taking while on tamoxifen. 

There are many drugs, including over the counter medications, and concentrated supplements, including those found in health food stores, that can lower activity of these enzymes and prevent you from getting the full benefit from tamoxifen.   

You can see some of the drugs that interact with the CYP enzymes here.  But, honestly, it’s easier just to have a chat with your pharmacist.  That is what they are there for, after all.

Foods Can Affect The CYP Cycle.  

There are some foods that can activate or inhibit CYP2D6.  However, for the most part, if you eat in moderation and eat a variety of foods, you should be fine.  There are studies published that focus on specific foods and the effects they have on the CYP cycle.  But if you dive in and read the research in depth, many of those studies are using levels of food concentrates that we just don’t consume when we eat normally

But there are some foods that have enough scientific evidence that justify tweaking our eating habits.  I have simplified this research into do’s and don’ts of eating while taking tamoxifen below. 

Be Careful with Food Supplements

But before we get to that, let me just say one thing.  Be careful with taking concentrated food supplements.  For example, you may have heard that turmeric is good for breast cancer patients.  And while that seems to be true, if you take tamoxifen, you should not take a concentrated turmeric supplement.  Turmeric in higher doses can inhibit CYP enzymes and limit the effectiveness of tamoxifen. 

It is a good idea to also discuss all supplements you may be taking with your oncologist or pharmacist. 

Okay, now let’s get to what you have been waiting for… The do’s and don’ts of eating while taking tamoxifen. 

The Do’s of Eating While Taking Tamoxifen

Eat More Vegetables, Fruits & Whole Grains

Many organizations recommend that cancer patients move to a plant-based diet.  That doesn’t mean eliminating meat entirely.  But, animal fats and proteins should be consumed in limited amounts.  I explain why later in “The Don’ts of Eating while taking Tamoxifen” below.

Plant foods, such as vegetables, fruits and whole grains, contain powerful phytochemicals that can help us fight cancer.  I have already written about many of them in the Healthy Eating Archives here at Pink Ribbon Runner.  Be sure to subscribe to my emails, as I have plans for many more articles about healthy food choices for cancer survivors. 

Soy & Flax Seed Are Okay

I do want to talk a bit about soy and flax seeds here.  You may have heard that breast cancer survivors should not eat these foods as they contain estrogen-like chemicals.  While it is true that these foods contain phytoestrogens, these plant-based estrogens don’t react with breast cancer cells like animal-based estrogens do.  Many studies have found that soy and flax seeds are safe to eat.

But wait!  There is more.  Not only do these studies say that it is okay to eat these foods, but they also go on to suggest that people taking tamoxifen should be eating these foods.  There is a synergy effect between tamoxifen and these foods that enhance the effectiveness of the drug at blocking the growth of breast cancer cells.  But, don’t go overboard.  Always eat foods in moderation. 

Portion Control

Tamoxifen Can Lead To Weight Gain

Tamoxifen can lead to weight gain, which can lead to higher risks of cancer recurrence.  Estrogens like to hang out in our fat.  The more fat we have, the more estrogen can be stored up for a rainy day.  So, keeping your weight in the healthy range is ideal. 

And as I say that, I know how extremely hard it can be to battle weight gain on tamoxifen.  I gained about 25 pounds when I was on it.  But, controlling how much we eat can limit the amount of weight we gain.  Had I just ate whatever I wanted, that 25 pounds may have been 50 or even 100 pounds. 

I have some tips for permanent weight loss without dieting in this article found here.

Tamoxifen Can Lead To Weight Loss

Some women lose weight on tamoxifen. This can also be a troubling side effect, if they were a normal healthy weight to begin with.  These women may need to also control their portions, but with larger portions of healthy foods.

We should always strive to eat portions that aim to maintain our weight, without added gain or loss, even when we are battling the side effects of tamoxifen.  Journaling can help you keep track.  I wrote about it in this article, 7 Benefits of Journaling Your Weight Loss Journey

Lower Total Daily Fat Intake

Since estrogens are stored in fat, it makes sense to limit the amount of animal fat we consume to avoid exposure to extra hormones.  There is also some scientific evidence that suggest that breast cancer patients on tamoxifen have better survival rates when fat is limited to less than 20% of total daily calories (the general recommendation is 20 – 35%).  It is best to stick to healthy plant-based fats, such as olive oil, canola and avocado. 

Drinking Coffee is Okay too

There have been a few studies that suggest drinking coffee can help prevent tamoxifen resistance. One study, published in the Cancer Causes & Control Journal, reported that tamoxifen-treated patients with ER+ breast cancer who drank 2 – 5+ cups of coffee per day had significant decreased risk for cancer recurrence. However, we need to be cautious in interpreting this finding. The researchers further went on to state that more research is needed to confirm this.

So, if you like to drink coffee, go ahead and drink coffee. If you don’t drink coffee, there is no reason to start the habit just yet.

The Don’ts of Eating While Taking Tamoxifen

Avoid Grapefruit

While I said that most foods are okay to eat in moderation, grapefruit is an exception.  Grapefruit and grapefruit juice are well known CYP disruptors.  Most pharmacists will tell you to stay away from grapefruit if you are taking any medications, including tamoxifen, that uses the CYP Catabolic Cycle.  Just one glass of grapefruit juice is enough to limit the effectiveness of tamoxifen. 

There are some studies that suggest mango and hot red peppers interfere with CYP2D6.  However, it isn’t known if these foods reduce the effectiveness of tamoxifen specifically.  If you like mango or hot peppers, then perhaps enjoy them in moderation. 

Careful With Tangerines & Seville Oranges

These oranges contain a compound called tangeretin that is a known CYP inhibitor.  However, this phytochemical is concentrated in the peel, with very little in the interior of the fruit.  So, you should be fine if you peel the orange and only eat the inside.  Where this may be a problem is if you eat a lot of marmalade or other products that contain the peels. 

Tangeretin can also be purchased as a supplement.  It is thought to have some anti-cancer properties, so may be tempting to take.  But, as I have warned already, sometimes these supplements are not a good idea if you are taking tamoxifen. 

Other oranges do not interfere with CYP enzymes and are fine to eat as a whole fruit. However, orange juice filters out the beneficial fiber and can concentrate other phytochemicals that can interfere with absorption of some medications.  It is always better to take medications with water and not fruit juices, unless otherwise instructed by a doctor or pharmacist. 

Limit Meat Protein

Leucine is one of the 9 essential amino acids.  It is found primarily in animal proteins, such as beef, chicken, pork and fish.  Plant proteins are low in leucine. 

Recent studies in cell culture and rodents suggest that tamoxifen resistance may occur when we eat a lot of leucine in our diet.  Controlled clinical trials have not been completed yet, so this is just scientific speculation at this point.  However, there are other reasons to limit the amount of meat we eat, especially red meats.

Limit Red Meats

Red meats, such as beef and pork, when cooked on high heat can produce carcinogenic compounds.  The scientific research is so compelling that the World Health Organization has released a statement saying that diets high in red meat have an increased risk for cancer. They further explain that we should avoid cooking these meats in direct contact with a flame or hot surface, such as in grilling or broiling.  I explain this further in my blog post Are We Cooking Ourselves Sick?

Limit Animal Fats

In addition, some meats contain added estrogens, which tamoxifen is trying to combat.  Some countries allow the meat industry to use growth hormones to boost growth of the animals.  Neither Canada nor the USA allow this in pork and chicken, but they do allow it in beef cattle.  Many European countries no longer allow this practice in any meat production.  Breast cancer patients should be aware of these practices and look for meats raised without hormones.  If this isn’t possible, then at least trim the fat off the meats, as the estrogens are stored in the fat, with little residue in the fleshy muscle.     

Limit Milk & Dairy

In the same way that beef may contain added estrogens, milk may also contain extra hormones.  Some countries, including the US, allow dairy farmers to boost production with growth hormones.  Canada and some European countries do not allow added hormones in milk. 

However, animal estrogens are found naturally in milk regardless. These may influence human health, perhaps even influencing the recurrence of breast cancer.   However, the research to date is not conclusive.

During the last couple of years, increasing body of evidence are indicating another property of hormones in dairy products as possible impact on human health including the role of some estrogens and insulin-like growth factor-1 in initiation and provoking of breast, prostate and endometrial tumours.

Source: Hormones in Dairy Foods and Their Impact on Public Health

There is also some evidence that milk may increase risk for breast cancer.  However, this research is not conclusive and there are an equal number of conflicting studies.  I wrote more about milk in my article on Milk: Healthy or Not?

Food Does Not Directly Cause Cancer

It is important to point out that what you ate did not directly cause your cancer.  Cancer is a complicated subject that scientists are still working hard to figure out.  But diet does play a role in cancer risk and surviving cancer.  We need to continue to eat as healthy as we can with the information we have today.  As I always say, I will fight with all the tools in my cancer fighting toolbox.  And that includes eating healthy foods.

I hope you found this article helpful.  Again, be sure to subscribe to receive my emails.  I have more information on healthy eating coming soon. 

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