Body weight and BMI

Body mass index (BMI) is a measure used to help show whether or not a person has a healthy weight.

BMI includes a measure of height and weight. So, BMI is better than weight alone when making comparisons. Calculate your BMI or find your BMI in a table.

For people ages 20 and older, weight status categories are: 

BMI	Body weight status
18.5 to 24.9	Normal
25.0 to 29.9	Overweight
30.0 and greater	Obese

  

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, women who are overweight or obese have a modestly decreased risk of breast cancer [66-70].
• After menopause, women who are overweight or obese have an increased risk of breast cancer [66-68,70].

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 [66-69].

Although being overweight or obese is linked to a lower risk of breast cancer before menopause, weight gain should be avoided.

Most breast cancers occur after menopause. Any weight gained before menopause may be carried into the postmenopausal years.

Hormone receptor status

Some findings suggest women who are overweight or obese may have an increased risk of estrogen receptor-negative breast cancers before menopause, including triple negative breast cancers [71-72].

Body weight and breast cancer risk after menopause

Women who are overweight or obese after menopause have a 20-60 percent higher breast cancer risk than those who are lean [66-68,70].

Hormone receptor status

Being overweight after menopause may be more strongly linked to an increased risk of estrogen receptor-positive breast cancers than the risk of estrogen receptor-negative cancers [70,72-73].

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 [72]. Those who were obese had a 20-80 percent greater risk of estrogen receptor-positive breast cancer [72].

This study also found, in general, women who were overweight or obese had an increased risk of estrogen receptor-negative breast cancers [72]. 

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 [19].

Women with higher estrogen levels have an increased risk of breast cancer compared to women with lower estrogen levels [19]. 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.

Insulin levels

Women who are heavier tend to have higher levels of insulin in their bodies compared to leaner women [74].

Some studies have shown an increased risk of breast cancer among postmenopausal women with high levels of insulin, including women with type 2 diabetes [75-78].

Among premenopausal women, a possible link between insulin levels and breast cancer risk is less clear [79].

Learn more about insulin and breast cancer risk.

These topics are under study.

Weight gain and breast cancer risk

Women who gain weight in adulthood have an increased risk of breast cancer before and after menopause [80-84].

A meta-analysis that combined the results from 16 studies found that for every 11 pounds a woman gained after age 18, breast cancer risk increased 7 percent [70].

Weight gain after menopause

It’s not just the weight a woman gains after age 18 that seems important to risk. The weight a woman gains after menopause also appears to be linked to an increased risk of breast cancer [80,85].

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 [80].

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 be linked to a lower risk of breast cancer [70,80,86-87]. 

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 [87]. Women who lost 4-20 pounds had a 10-15 percent lower risk and those who lost more than 20 pounds had about a 25 percent lower risk [87].

Not all studies have shown weight loss after menopause is linked to a lower risk of breast cancer though [87].

Weight loss before menopause

Weight loss in adulthood and the risk of breast cancer before menopause is under study [70,88].

Body shape, body composition and breast cancer risk

Body shape

Body shape may also be related to breast cancer risk. Researchers often use measures such as waist circumference (around the waist), hip circumference (around the hip) and waist-to-hip ratio (a comparison of waist and hip circumference) to estimate body shape.

Some findings show women who put on extra weight around their middle sections (sometimes called central adiposity or “apple-shaped”), as opposed to their hips and thighs (sometimes called “pear-shaped”), have a small to moderate increased risk of breast cancer [89-92].

Other findings show, after BMI is taken into account, body shape isn’t related to breast cancer risk [93].

This topic is under study.

Body composition

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 [94-95].

This topic is under study.

Overweight, obesity and health

Maintaining a healthy weight is linked to a lower risk of breast cancer after menopause and is one of the best things you can do for your health overall.

Women who are overweight or obese have an increased risk of many cancers and other health conditions, including [96-97]:

Cancers

• Breast cancer
• Colon and rectal cancer
• Endometrial (lining of the uterus) cancer
• Esophageal cancer
• Gallbladder cancer
• Kidney cancer
• Liver cancer
• Meningioma (cancer in the lining of the brain and spinal cord)
• Multiple myeloma (cancer of the plasma cells)
• Ovarian cancer
• Pancreatic cancer
• Stomach cancer
• Thyroid cancer

Other health conditions

• Diabetes
• Heart disease
• Stroke

Women who are overweight or obese may also have an increased risk of [97]:

• Mouth, throat and voice box cancers
• Non-Hodgkin lymphoma

Body weight and breast cancer survival

Maintaining a healthy weight is important after a breast cancer diagnosis.

Learn about body weight and breast cancer recurrence and survival.  

For a summary of research studies on body weight and breast cancer survival, visit the Breast Cancer Research Studies section.

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.

 

SUSAN G. KOMEN®‘S BREAST SELF-AWARENESS MESSAGES

1. Know your risk Talk with both sides of your family to learn about your family health history   Talk with a health care provider about your risk of breast cancer 2. Get screened Talk with a health care provider about which screening tests are right for you if you’re at higher risk   Have a mammogram every year starting at age 40 if you’re at average risk Have a clinical breast exam at least every 3 years starting at age 20, and every year starting at age 40 Sign up for your screening reminder at komen.org/reminder 3. Know what is normal for you and see a health care provider if you notice any of these breast changes (see images): Lump, hard knot or thickening inside the breast or underarm area Swelling, warmth, redness or darkening of the breast Change in the size or shape of the breast Dimpling or puckering of the skin Itchy, scaly sore or rash on the nipple Pulling in of the nipple or other parts of the breast Nipple discharge that starts suddenly New pain in one spot that doesn’t go away 4. Make healthy lifestyle choices Maintain a healthy weight Add exercise into your routine Limit alcohol intake Limit menopausal hormone therapy (postmenopausal hormone use) Breastfeed, if you can

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.

Updated 03/01/21