Body Weight and Weight Gain
Body weight and BMI
Body mass index (BMI) is a measure used to help show whether or not a person has a healthy weight.
For people ages 20 and older, weight status categories are:
Body weight status
18.5 to 24.9
25.0 to 29.9
30.0 and greater
Body weight, breast cancer risk and menopausal status
Studies show a link between BMI and breast cancer risk. However, BMI affects risk differently before and after menopause.
- Before menopause, being overweight or obese modestly decreases breast cancer risk [64-67].
- After menopause, being overweight or obese increases breast cancer risk [64-66].
Read Komen’s perspective on body weight and breast cancer risk.*
Body weight and breast cancer risk before menopause
Women who are overweight or obese before menopause have a 20-40 percent lower risk of breast cancer than those who are lean [64-67].
Although being overweight or obese may lower breast cancer risk before menopause, weight gain should be avoided.
Most breast cancers occur after menopause. Any weight you gain before menopause you may carry into your postmenopausal years.
Hormone receptor status
Body weight and breast cancer risk after menopause
Women who are overweight or obese after menopause have a 30-60 percent higher breast cancer risk than those who are lean [64-66].
Hormone receptor status
One large study found postmenopausal women who were overweight had a 10-30 percent greater risk of estrogen receptor-positive breast cancer compared to those who were lean . Those who were obese had a 20-80 percent greater risk of estrogen receptor-positive breast cancer .
This study also found, in general, women who were overweight or obese had an increased risk of estrogen receptor-negative breast cancers .
For a summary of research studies on body weight and breast cancer, visit the Breast Cancer Research Studies section.
How can body weight affect breast cancer risk after menopause?
Blood estrogen levels
Before menopause, most estrogens in the body are produced in the ovaries.
After menopause, the ovaries no longer produce much estrogen and estrogens mainly come from fat tissue.
Fat tissue contains an enzyme called aromatase that converts hormones called androgens (made mostly in the adrenal glands) to estrogens. So, heavier women have higher blood estrogen levels than leaner women .
Women with higher estrogen levels have an increased risk of breast cancer compared to women with lower estrogen levels . So, the extra estrogen likely explains at least some of the increased breast cancer risk among postmenopausal women who are overweight.
Learn more about estrogen and breast cancer risk.
Women who are heavier tend to have higher levels of insulin in their bodies compared to leaner women .
Some studies have shown an increased risk of breast cancer among postmenopausal women with high levels of insulin, including women with type 2 diabetes [72-74].
Among premenopausal women, a possible link between insulin levels and breast cancer risk is less clear .
Learn more about insulin and breast cancer risk.
These topics are under study.
Weight gain and breast cancer risk
Gaining weight in adulthood increases the risk of breast cancer before and after menopause [76-79].
One large study found women who gained about 20 pounds after age 18 had a 15 percent higher risk of breast cancer compared to women who gained little or no weight . Women who gained 55 pounds or more had a 45 percent higher risk .
Weight gain after menopause
It’s not just the weight a woman gains after age 18 that seems to be important to risk. The weight a woman gains after menopause also appears to increase the risk of breast cancer [76,80].
One large study showed women who gained 20 pounds or more after menopause had an 18 percent higher risk of breast cancer compared to those who gained little or no weight after menopause .
For a summary of research studies on weight gain and breast cancer, visit the Breast Cancer Research Studies section.
Weight loss and breast cancer risk
Weight loss after menopause
Losing weight after menopause may lower the risk of breast cancer [76,81-82].
A pooled analysis of more than 180,000 postmenopausal women found those who lost weight (and kept the weight off) had a lower risk of breast cancer than women whose weight didn’t change much over time . Women who lost about 4-20 pounds had about a 10-15 percent lower risk and those who lost more than about 20 pounds had about a 25 percent lower risk .
Not all studies have shown weight loss after menopause lowers breast cancer risk .
Weight loss before menopause
Weight loss in adulthood and the risk of breast cancer before menopause is under study .
Body shape, body composition and breast cancer risk
Body shape may also affect breast cancer risk.
Some findings show women who put on extra weight around their middle sections (sometimes called “apple-shaped”), as opposed to their hips and thighs (sometimes called “pear-shaped”), have a small to moderate increased risk of breast cancer [84-87].
Other findings show that after BMI is taken into account, body shape does not increase breast cancer risk .
This topic is under study.
BMI estimates body weight status, but it has some limits. For example, it doesn’t include measures of fat and muscle in the body. So, a person with a lot of muscle and little fat can have the same BMI as a person with a lot of fat and little muscle.
Body composition, including the amount of fat versus the amount of muscle in a person’s body, can be measured with a CT scan. Body composition may be an important measure in studies of body weight status and breast cancer [89-90].
This topic is under study.
Overweight, obesity and health
Maintaining a healthy weight lowers the risk of breast cancer after menopause and is one of the best things you can do for your health overall.
Being overweight or obese increases the risk of [91-92]:
- Heart disease
- Colon and rectal cancer
- Endometrial (lining of the uterus) cancer
- Esophageal cancer
- Kidney cancer
- Pancreatic cancer
Being overweight or obese may also increase this risk of :
- Gallbladder cancer
- Liver cancer
- Multiple myeloma
- Non-Hodgkin lymphoma
- Ovarian cancer
- Prostate cancer
Body weight and breast cancer survival
Maintaining a healthy weight is important after a breast cancer diagnosis.
For a summary of research studies on body weight and breast cancer survival, visit the Breast Cancer Research Studies section.
Read Komen’s perspective on body weight and breast cancer survival.*
It’s never too late to adopt a healthy lifestyle
Making healthy lifestyle choices has benefits at any age.
Being active, eating a balanced diet and making other healthy lifestyle choices can be physically and mentally rewarding at any point in life.
Learn more about healthy lifestyle choices and breast cancer risk.
1. Know your risk
2. Get screened
3. Know what is normal for you and see a health care provider if you notice any of these breast changes (see images):
4. Make healthy lifestyle choices
Download Komen’s Breast Self-Awareness Messages card for more information.
*Please note, the information provided within Komen Perspectives articles is only current as of the date of posting. Therefore, some information may be out of date.