Breast Cancer Risk Factors: Body Weight and Weight Gain
The link between body weight and the risk of breast cancer is complex. Breast cancer risk is related to both:
- Body weight (and menopausal status)
- 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.
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
Being overweight differs in the way it’s linked to breast cancer risk before and after menopause.
- Before menopause, women who are overweight or obese have a modestly decreased risk of breast cancer [74-78].
- After menopause, women who are overweight or obese have an increased risk of breast cancer [74,76-79].
These risks may vary by race and ethnicity.
Learn about other factors linked to the risk of breast cancer.
Body weight and breast cancer risk before menopause
Women who are overweight or obese before menopause have a 10%-20% lower risk of breast cancer than those who are lean [74-78].
Although being overweight or obese is linked to a lower risk of breast cancer before menopause, weight gain should be avoided [27]. This is because any weight gained before menopause may be carried into the postmenopausal years, and most breast cancers occur after menopause.
After menopause, being overweight is linked to increased breast cancer risk.
The American Cancer Society recommends everyone achieve and maintain a healthy weight throughout life [27].
Hormone receptor status
Women who are overweight or obese before menopause have a lower risk of overall breast cancer than those who are lean [74-78].
However, some findings suggest women who are overweight or obese may have an increased risk of estrogen receptor-negative breast cancer before menopause, including triple negative breast cancer [80-81].
Body weight and breast cancer risk after menopause
Women who are overweight or obese after menopause have a 20%-60% higher breast cancer risk than those who are lean [74,76-79].
The American Cancer Society recommends everyone achieve and maintain a healthy weight throughout life [27].
 | 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 [40,82].
Women with higher estrogen levels have a higher risk of breast cancer than women with lower estrogen levels [22]. 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 (including insulin levels related to type 2 diabetes)
Heavier women tend to have higher levels of insulin in their bodies compared to leaner women [82].
Some studies have shown an increased risk of breast cancer among postmenopausal women with high levels of insulin, including women with type 2 diabetes [83-86].
Among premenopausal women, a possible link between insulin levels and breast cancer risk is less clear [87].
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 after menopause [88-92].
A meta-analysis that combined the results from 16 studies found that for every 11 pounds a woman gained after age 18, the risk of breast cancer after menopause increased 7% [76].
Weight gain in adulthood and a possible link to the risk of breast cancer before menopause is under study [78,91,93-95].
Learn about other factors linked to the risk of breast cancer.
Weight gain after menopause
It’s not just the weight a woman gains after age 18 that seems important to risk. Weight gain after menopause also appears to be linked to an increased risk of breast cancer [88,96].
One large study showed women who gained 20 pounds or more after menopause had an 18% higher risk of breast cancer compared to those who gained little or no weight after menopause [88].
| 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 [76,88,97-98].
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 [98]. Women who lost 4-20 pounds had a 10%-15% lower risk, and those who lost more than 20 pounds had about a 25% lower risk [98].
Not all studies have shown weight loss after menopause is linked to a lower risk of breast cancer [98].
Weight loss before menopause
Weight loss in adulthood and the risk of breast cancer before menopause is under study [76,93].
Body shape, body composition and breast cancer risk
Body shape
Body shape may 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 circumferences) 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 [99-103].
Better ways of measuring body shape are under study to help learn more about body shape and breast cancer risk.
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 in a few ways, including with a CT scan. Body composition may be an important measure in studies of body weight status and breast cancer [102,104-105].
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 overall health.
Women who are overweight or obese have an increased risk of many cancers and other health conditions, including [106-107]:
Cancers
- Breast cancer
- Colon and rectal cancers
- 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
- Heart disease
- Stroke
- Type 2 diabetes
Women who are overweight or obese may also have an increased risk of [106]:
- 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.
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1. Know your risk
2. Get screened
* Per National Comprehensive Cancer Network Guidelines 3. Know what is normal for you See a health care provider if you notice any of these breast changes:
To see illustrations of these warning signs, please visit the Warning Signs of Breast Cancer page. 4. Make healthy lifestyle choices
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Download our Breast Self-Awareness Messages resource 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 12/18/24
This content is regularly reviewed by an expert panel including researchers, practicing clinicians and patient advocates.