Obesity, Cancer

What is obesity?

Obesity is when a person's body fat distribution or amount is unhealthy ( 1). Being overweight or obese puts people at higher risk for various diseases. These include diabetes, high blood sugar, heart disease, stroke, and at least thirteen types of cancer.

Researchers use the Body Mass Index to determine whether someone is obese. The BMI is calculated using a person's weight (in kg) divided by their height (in m) squared. It is commonly expressed as 2. BMI is a better indicator of obesity than just weight, and it's a good (if imperfect) measure for most people.

How common are obesity and severe obesity in the United States?

In recent years, obesity and severe obesity have increased in the United States ( 7).

In 2011, 27,4 % of adults aged 18 and older were obese or severely overweight.
In 2020, however, 31.9% of adults aged 18 and older will be obese or severely overweight.

In addition, the percentage of children and teenagers aged 2-19 who are obese or have severe obesity is also on the rise ( 6).

In 2011, 16.9% of children aged 2-19 had obesity, and 5.6% were severely obese.
In 2017, 18.3% of children aged 2-19 years were obese, and 6.1% of them had severe obesity.

The CDC reports that the prevalence of obesity in the United States varies by race and ethnicity ( 7). The proportion of adults aged 18 or older who were obese or had severe obesity was:

Non-Hispanic Black, 41.6%
American Indian/Alaska Native, 38.8%
Hawaiian/Pacific Islander, 38.5%
Hispanic, 36.6%
Non-Hispanic White, 30.7%
Asian, 11.8%

In 2017, the percentage of obese children and adolescents aged 2-19 was ( 6).

Mexican Americans, 26.9%
Hispanic, 25.6%
Non-Hispanic Black, 24.2%
Non-Hispanic White, 16.1%
Non-Hispanic Asian, 8.7%

The COVID-19 ( 8) pandemic may have caused a rapid increase in obesity prevalence. The CDC provides estimates of the prevalence of adult obesity in the United States.

What do we know about the link between obesity and cancer?

Most evidence that links obesity with cancer risk is derived from large cohorts, a type of observational study. Observational studies can't prove that obesity is a cause of cancer. People with obesity and overweight may differ from those without these conditions in other ways than body fat. These other differences could explain their increased cancer risks rather than body fat.

What are the possible ways that obesity can increase cancer risk?

Several possible mechanisms could explain why obesity increases the risk of certain cancers ( 32 and 33).

The fat tissue (also known as adipose tissue) produces excessive amounts of estradiol. High levels have been linked to an increased risk of breast, endometrial, and ovarian cancers.
Obese people often have elevated blood levels of Insulin and Insulin-like Growth Factor-1. Hyperinsulinemia is a condition caused by insulin resistance. It precedes type 2 diabetes and other cancer risk factors. High levels of IGF-1 and Insulin may contribute to the development of cancers of the colon, kidney, endometrium, and prostate ( 34).
These conditions can cause biliary tract cancer and other cancers. These conditions may cause oxidative stress, which can lead to DNA damage.
Adipokines are hormones fat cells produce that can stimulate or inhibit cell proliferation. Leptin, for example, is an adipokine that increases blood levels with increasing body weight. High levels of leptin may promote abnormal cell growth. Adiponectin is another adipokine that is lower in obesity than healthy weight people. It may have an antiproliferative effect and protect against tumor growth.
The fat cells can also affect other metabolic and cell growth regulators, such as the mammalian Target of Rapamycin and AMP-activated Protein Kinase.

The other mechanisms that obesity may affect cancer risk are changes in the mechanical properties of the scaffolding tissue surrounding developing tumors and the 37.

Obesity can have biological effects but also cause problems in terms of screening and management. Women with obesity or overweight are at a higher risk of developing cervical cancer than women with a healthy weight. It is likely because they have less effective screening for cervical cancer ( 38).

How many cancers are caused by obesity?

According to a nationwide cross-sectional analysis using BMI data and cancer incidents from the US Cancer Statistics Database, each year between 2011 and 2015, approximately 37,670 men (4.7%) and 74,690 women (9.6%) had an excess body weight. A nationwide cross-sectional study using BMI and cancer incidence data from the US Cancer Statistics database estimated that each year from 2011 to 2015, about 37,670 new cancer cases in men (4.7%) and 74,690 new cancer cases in women (9.6%) were due to excess body weight (

A 2019 study revealed that globally 2012, excess weight was responsible for 3.9% of cancers (544 300 cases). The burden of cancer cases for women was higher (368 500 cases) than for men (175,800). ( 40). A 2019 study found that excess body weight was responsible for 3.9% of all cancers (544,300 cases) in 2012. The burden of these cancer cases was higher among women (368,500 cases) than men (175,800) (a href=" https://www.cancer.gov

Can losing weight reduce the risk of cancer?

Most data on whether losing weight can reduce cancer risk comes from cohort or case-control studies. Observational Studies on obesity and cancer should be interpreted because they can't definitively prove that obesity causes cancer. People who lose weight could also differ from those who don't.

In some studies, people who have lost weight and are obese had a lower risk of cancers such as breast, endometrial, or colon cancer. In one large prospective trial of postmenopausal women, intentional weight loss greater than 5% was associated with a lower risk of obesity-related cancers. It included endometrial carcinoma ( 41). In this study, however, unintentional weight loss was not linked to cancer risk.

A follow-up study on weight and breast carcinoma in the Women's Health Initiative (42) found that weight gain or loss (for women who were overweight or obese before the study) did not affect breast cancer risk. In a study combining data from 10 cohorts of women aged 50 and older, sustained weight loss has been associated with a lower risk of breast cancer ( 43).

Researchers are studying the cancer risks of people who have had bariatric surgeries, surgery performed on the stomach and intestines to achieve maximum weight loss. Bariatric surgery is associated with a reduced risk of cancer in people with obesity. It includes women.

What is the impact of obesity on cancer survivors?

The majority of evidence on obesity among cancer survivors is from those who have been diagnosed with colorectal, breast, or prostate cancer. Researchers have found that obesity can negatively impact several aspects of cancer survivorship, including cancer progression, quality of life, and cancer recurrence.

In a large clinical trial of patients with stage II and stage III rectal cancer, those with a higher baseline BMI (particularly men) had an increased risk of a data-glossary-id= "CDR0000559442" href= "https://www In a large trial of patients with rectal cancer stage II or stage III, those with higher BMIs (especially men) were at an increased risk for local recurrence. (51). People with obesity are 50% more likely to die from multiple myeloma than people with a healthy weight. (52).

Weight loss following a cancer diagnosis is beneficial for overweight or obese people.

The majority of studies on this topic have been focused on breast cancer. Weight loss interventions in breast cancer survivors resulted both in weight loss and positive changes in biomarkers linked to the relationship between obesity and prognosis.

Limited evidence shows that weight loss can reduce the risk of breast carcinoma, recurrence, or death (55). The NCI-sponsored Breast Cancer Weigh Loss (BWEL), an ongoing random phase-III trial, examines whether weight loss after breast cancer diagnosis impacts invasive Disease-Free Survival or recurrence (56).

What research is done on obesity and cancer today?

Numerous studies explore mechanisms linking obesity and cancer ( 35, 56). The gut microbiota (also known as the microbiome), a collection of microbes living in the gastrointestinal tract, plays a role in type 2 diabetes and weight gain. Dysbiosis is a community imbalance that occurs when these microbes are infected. The gut microbiomes are different and less diverse in obese people than in healthy people. Imbalances of the gut microbiota have been linked to inflammation and altered metabolism. These may be associated with cancer.

Researchers are studying the impact of obesity on the tumor environment. It may affect cancer progression. Studies in mouse models have shown that obesity (induced through feeding mice high-fat diets) causes a competition between tumor cells and cells for lipids, which makes T cells less effective against cancer ( 58).

The role of insulin receptors in cancer is another area that needs to be investigated. Many cancer cells have elevated levels of IR, a form of insulin receptor with a high affinity to insulin and growth factors. Researchers are looking at how these factors can contribute to cancer and metabolic diseases and if they could be used as therapeutic targets to prevent obesity-related cancers.

Researchers are also exploring if the associations between obesity and cancer outcomes or risk vary by race ( 59). Researchers are also investigating whether different ethnic/racial groups should use different thresholds for obesity and overweight. For example, the World Health Organization (WHO) has proposed alternate thresholds for overweight and obese people with Asian ancestry of 27.5 and 23.0 kg/m 2.

The NCI Cohort Consortium is an extramural-intramural partnership that combines more than 50 prospective cohort studies from around the world with more than seven million participants. These studies gather information about body mass index, waist size, and other measures of adiposity. Researchers will be able to understand better how obesity-related factors are related to lesser common cancers such as thyroid, kidney, head and neck, and gallbladder cancers.

A second area of research focuses on developing more effective and precise interventions to prevent weight gain or regain following weight loss. The research in this area includes two NIH initiatives - the Accumulating Data to optimally predict obesity treatment (ADOPT), Core Measures( 61), and the Trans NIH Consortium of Randomized controlled trials of lifestyle weight loss interventions ( 62). Both of these initiatives aim to identify and incorporate genetic, psychosocial, and behavioral factors, as well as biological and environmental factors, into predictive profiles that will enable more accurate

NCI supports obesity-related cancer research through a range of activities. These include large collaborative initiatives, web resources and data, epidemiologic studies, basic science, and dissemination and implementation resources. For example, Transdisciplinary Energetics Research and Cancer (TREC) supports ongoing training workshops to improve the ability to produce innovative transdisciplinary research on energetics, cancer, and clinical care. The Trans NCI Obesity and Cancer Working Group encourages cross-cutting interest in obesity and research on cancer within NCI. It is done by sharing and identifying the current state of the science about obesity and cancer.

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