If you’re taking anastrozole (Arimidex) to treat hormone receptor-positive breast cancer, it’s normal to worry about the potential side effects. One frustrating side effect of a hormone therapy like anastrozole is that it can cause unwanted weight gain or make it very hard to lose weight, if that’s a goal. You might then be less motivated to keep taking the medication or find it harder to keep yourself healthy while you’re on it.

Here’s what you need to know if you’re trying to manage your weight while on anastrozole, or another aromatase inhibitor, so you can keep your quality of life high.

What Is Anastrozole?

Anastrozole is an aromatase inhibitor. This category of medications helps prevent breast cancer before and after menopause in people under treatment to suppress their ovaries. It also helps prevent a recurrence (return of disease) in breast cancer survivors by interfering with estrogen receptors (proteins). Anastrozole is similar to tamoxifen but works in slightly different ways. Other common aromatase inhibitors are letrozole (Femara) and exemestane (Aromasin).

Although anastrozole and other aromatase inhibitors don’t commonly cause weight gain, these drugs may contribute to it. This side effect can be discouraging for people who are trying to feel at home in their bodies again after breast cancer treatment.

Some studies suggest that weight gain while on aromatase inhibitors usually is minimal or might not occur, but many people do report gaining weight. Study results may not accurately represent the experiences of weight gain for a number of reasons, such as differences regarding participants’ ages or estrogen levels (whether they had been through menopause).

Several MyBCTeam members have experienced weight gain and frustration. One said, “Anastrozole and its alternatives make it very hard to lose weight. I’ve tried unsuccessfully for two years. I met with a dietitian, strictly followed her recommended diet, and exercised every day for six months. I lost only 1.5 pounds. I felt fatigued and lifeless the whole time.”

“Well, I sure have been successful gaining weight on anastrozole … to the tune of about 35 pounds!” another member said.

When people do gain weight on aromatase inhibitors, they seem more likely to do so during the first year of treatment. Other risk factors for gaining a significant amount of body weight included:

• Being younger than 60
• Having had a mastectomy during breast cancer treatment
• Smoking cigarettes

Since weight management is often important both for personal reasons and for preventing or managing other medical conditions, finding effective ways to address unwanted weight gain is key.

Tips for Managing Weight Gain From Anastrozole

You can take a number of steps to help reach or maintain a healthy weight while taking anastrozole or another aromatase inhibitor, as well as after you stop taking these medications.

1. Track How Much You’re Eating

Logging all your snacks and meals can help you see when and where you might be eating more than you think or less healthfully than you’d like. Making small changes in these areas can lead to significant shifts in your weight. You may not have to actually count calories to see success. If adding up calories seems like too much trouble, you can try other strategies, such as using your phone’s camera to keep a photo diary of your food or simply listing everything you eat.

2. Limit Alcohol

Many alcoholic beverages have a lot of calories that don’t do much good in your body. Eliminating them, especially if you tend to drink regularly, could be helpful as you try to change or manage your weight. You can instead choose low-calorie nonalcoholic beverages or even lower-calorie alcoholic drinks, such as a spirit (like vodka) with a no-calorie mixer (like soda water).

3. Get More Exercise

If you’ve been dealing with breast cancer, greater fatigue may have led to less exercise. Adding more physical activity back into your life is a good way to help manage your weight. You can start small and slowly develop an exercise program, which may help you feel better and contribute to a healthy weight.

4. Eat More Fiber

If you’re often tempted to overeat and aren’t sure why, see if increasing your fiber intake helps. Try eating more fruits and vegetables, whole grains, and legumes. Fiber helps your stomach feel fuller, so you might be able to eat less to feel satisfied. Getting plenty of fiber is part of a healthy, balanced diet when you’re being treated for or recovering from breast cancer.

5. Balance Your Blood Sugar

If you feel like you’ve tried everything but still can’t lose or manage your weight, consider learning more about blood glucose (blood sugar) levels, insulin (a hormone that helps regulate glucose levels), and insulin resistance (when your body’s cells don’t respond well to insulin). Insulin resistance can develop for a number of reasons and lead to type 2 diabetes. One member of MyBCTeam said, “I began to understand that insulin resistance might be the key.”

Even if your insulin is stable, you may want to eat in a way that keeps your blood sugar levels steady throughout the day. This often means choosing more foods that are traditionally considered healthy and fewer easy-to-digest carbohydrates, such as sugary treats and white bread, which can cause insulin to spike (rise sharply).

6. Make Thoughtful Food and Drink Choices

Managing your weight doesn’t mean depriving yourself. Just focus on simple strategies like these:

• Choose beverages with less sugar.
• Order wisely when dining out.
• Replace junk food with healthy snacks.

These changes alone can make quite a difference when you’re trying to manage your weight during or after treatment with aromatase inhibitors.

7. Consider Other Causes of Weight Gain

Since it’s unclear whether aromatase inhibitors directly cause weight gain, you may want to consider other reasons for your weight changes or difficulty losing weight. A wide variety of medications can cause unwanted weight gain, and many aren’t related to breast cancer. Hormonal changes unrelated to breast cancer or aromatase inhibitors can also lead to increased weight. You might also gain weight if you recently quit smoking.

If you’re gaining weight and aren’t sure why, talk to a health care professional or your oncology team. They may run tests to determine the cause, which could lead to more effective solutions. A professional like a dietitian or a wellness coach may also be able to help you better manage your weight and feel your best.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 64,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

Have you gained weight while taking an aromatase inhibitor like anastrozole? Do you have any tips to manage unwanted weight gain? Share your experience in the comments below, or start a conversation by posting on your Activities page.