Introduction
Obesity has become a major public health concern worldwide. According to the World Health Organization, over 650 million adults were obese in 2016, which is about 13% of the world's adult population. The prevalence of obesity has nearly tripled since 1975. In the United States, the obesity rate stands at 42.4% as of 2017-2018.
Obesity significantly increases the risk of various health problems like heart disease, stroke, type 2 diabetes, and certain types of cancer. It is associated with poorer mental health and reduced quality of life. The health consequences range from increased risk of premature death to serious chronic conditions that reduce the overall quality of life.
This article will examine the link between obesity and mortality. It will analyze how obesity affects the risk of all-cause and cause-specific mortality like cardiovascular mortality and cancer mortality. The impact of weight loss on reducing mortality risk will also be explored. Understanding the magnitude of the effect of obesity on mortality is crucial for public health efforts to reduce obesity rates and improve population health.
Definition of obesity
Obesity is defined as having excess body fat that negatively impacts health. The most common way to measure obesity is through body mass index (BMI), which is calculated by dividing a person's weight in kilograms by the square of their height in meters (kg/m2). According to the CDC, an adult with a BMI of 30 or higher is considered obese https://www.cdc.gov/obesity/basics/adult-defining.html.
Obesity has reached epidemic proportions globally, with an estimated 650 million adults being obese. According to the WHO, the worldwide prevalence of obesity nearly tripled between 1975 and 2016 https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight. In the United States, obesity affects 42.4% of adults. High income countries tend to have higher rates of obesity compared to low-middle income countries.
Health risks associated with obesity
Obesity is associated with an increased risk of developing several serious health conditions. According to the CDC, people with obesity are at higher risk of developing heart disease, type 2 diabetes, some cancers, high blood pressure, high cholesterol, stroke, sleep apnea, osteoarthritis, and fatty liver disease (source).
The mechanisms linking obesity to various diseases are complex and multifactorial. However, research has identified some key pathways. For example, excess body fat, especially abdominal fat, can induce a state of chronic low-grade inflammation in the body. This contributes to insulin resistance, atherosclerosis, and other processes underlying conditions like type 2 diabetes and cardiovascular disease (source).
Obesity is also associated with hormonal changes that can promote tumor growth and progression in certain cancers like breast, colorectal, and endometrial cancer. Obese individuals tend to have higher circulating levels of insulin and insulin-like growth factors that may stimulate cancer development (source).
Furthermore, the excess weight carried around by obese individuals can put mechanical strain on joints and contribute to osteoarthritis. It can also cause sleep apnea as fatty deposits in the neck narrow the airway (source).
Obesity and all-cause mortality
Several studies have shown that obesity is associated with increased all-cause mortality. A large meta-analysis published in 2013 looked at 97 studies including nearly 3 million people (Flegal et al., 20131). It found that obesity (BMI ≥30 kg/m2) was associated with significantly higher all-cause mortality compared to normal weight individuals, with an 18% increased risk. Another recent study analyzing data from over 9 million people found that obesity increased the risk of all-cause mortality by 21-108% compared to normal weight (Visaria et al., 20232).
The impact of obesity on mortality is substantial. One study estimated that obesity accounts for over 47,000 excess deaths per year in the United States (Flegal et al., 20053). It has been estimated that moderate obesity (BMI 30-35 kg/m2) reduces life expectancy by an average of 3 years, while severe obesity (BMI 40-45 kg/m2) reduces life expectancy by 8-10 years (Fontaine et al., 20034).
Obesity and cardiovascular mortality
Obesity significantly increases the risk of cardiovascular mortality, particularly from heart disease and stroke. According to the American Heart Association, obesity is associated with an increased risk of coronary heart disease, heart failure, and sudden cardiac death [1]. Epidemiological studies have consistently shown that obesity leads to 2-3 times higher rates of heart disease and stroke mortality [2].
Data from the National Health and Nutrition Examination Survey found that cardiovascular mortality rates were significantly higher among individuals with obesity compared to normal weight individuals. For example, the mortality rate from coronary heart disease was nearly 3 times higher in people with severe obesity [1]. Another analysis showed obesity was associated with a 49% increase in cardiovascular mortality over a 10 year period [2].
The evidence clearly demonstrates that obesity leads to substantial increases in mortality from cardiovascular diseases, especially heart disease and stroke. Public health efforts to reduce obesity rates could significantly lower cardiovascular mortality.
Obesity and Cancer Mortality
Obesity has been linked to an increased risk of developing several types of cancer, including colorectal, breast, endometrial, esophageal, kidney, pancreatic, gallbladder, thyroid, and multiple myeloma cancers (1). The biological mechanisms that explain this link are complex and multifactorial.
Excess body fat leads to metabolic dysregulation that can promote cancer development and progression. Obese individuals often have elevated levels of insulin, insulin-like growth factors, and sex hormones such as estrogen, all of which can stimulate cell proliferation and inhibit apoptosis (2). Obesity is also associated with chronic low-grade inflammation which can damage DNA and promote tumor growth.
Adipose tissue produces adipokines and cytokines that contribute to the pro-inflammatory state. Furthermore, obese individuals tend to have decreased immune function which impairs cancer immune surveillance (3). Fat cells may also directly interact with and stimulate the growth of cancer cells in some tissues.
Losing weight has been shown to reduce the risk of developing obesity-related cancers. Even a 5-10% weight loss can provide meaningful risk reduction. For example, women who lost weight had up to a 25% lower chance of postmenopausal breast cancer compared to women who gained weight (4). Maintaining a healthy body weight is an important cancer prevention strategy.
(1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9857053/
(2) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8008284/
(3) https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2777839
(4) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9857053/
Impact of weight loss on mortality
There is evidence that losing weight can reduce the risk of mortality in obese individuals. A 2015 review in PMC found that intentional weight loss was associated with an approximately 15% reduction in all-cause mortality in obese adults (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4368053/). This suggests that weight loss interventions may have important health benefits.
However, it's important that the weight loss is sustained over time. A 1999 study published in NEJM found that among individuals who are not severely obese, weight loss is associated with an increased mortality rate while fat loss is associated with a decreased mortality rate (https://pubmed.ncbi.nlm.nih.gov/10411233/). This highlights the importance of losing fat mass rather than just total body weight.
Overall, the evidence suggests that intentional and sustained weight loss, especially fat loss, can help reduce mortality risk in obese individuals. Public health efforts should focus on helping people achieve and maintain a healthy body weight through lifestyle changes.
Public health efforts on obesity
Public health authorities have implemented various campaigns and policies to try to reduce obesity rates. Some strategies focus on education and raising awareness, such as the CDC's "Let's Move" campaign started by Michelle Obama which promotes physical activity and nutrition for children (1). Other policies aim to make healthy choices easier through taxation, labeling laws, and changing food environments.
Many localities have imposed taxes on sugary beverages in an effort to reduce consumption. For example, Philadelphia implemented a 1.5 cent per ounce tax on sugary and diet drinks in 2017 (2). Studies have found that such taxes can lead to reduced purchases of taxed beverages (3).
Labeling laws like requiring calorie counts on restaurant menus also intend to discourage overconsumption by making nutritional information more readily available to consumers. The impact of menu labeling has been mixed, with some research showing it reduces calories purchased and other studies finding no effect (4).
On the treatment side, standard weight loss interventions include dietary changes, increased physical activity, medications and surgery. Dietary approaches focus on reducing calorie intake by eating more vegetables, fruits and lean protein. Finding a diet that works for the individual is key. Regular exercise also helps burn calories and prevent weight regain after loss (5). For very obese patients (BMI over 40), bariatric surgery is an option that typically leads to significant long-term weight reduction (6).
A combination of population-level policies and individual-level interventions will likely be needed to reverse the obesity epidemic. More research is needed to determine the most effective and feasible prevention strategies.
(1) https://letsmove.obamawhitehouse.archives.gov/
(2) https://www.phila.gov/services/payments-assistance-taxes/business-taxes/soda-tax/
(3) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6220709/
(4) https://www.cdc.gov/obesity/downloads/menu-labeling-evidence-review-2013.pdf
(5) https://www.ncbi.nlm.nih.gov/books/NBK220174/
(6) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3406229/
Conclusion
In conclusion, obesity significantly increases the risk of mortality from all causes. Obese individuals have a higher risk of dying from cardiovascular disease, certain cancers, and other chronic conditions compared to those with a healthy weight.
The obesity epidemic is a major public health crisis that requires urgent action. We must promote healthy lifestyles from a young age, make healthy foods more accessible, and create environments that encourage physical activity. On an individual level, maintaining a healthy weight through diet and exercise can help reduce mortality risk.
Addressing obesity on a societal level requires effort from individuals, communities, healthcare systems, governments, and various stakeholders. But the payoff for future generations is immeasurable - longer, healthier lives free of preventable diseases. The time to act is now.
References
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[2] Prospective Studies Collaboration, Whitlock G, Lewington S, Sherliker P, Clarke R, Emberson J, Halsey J, Qizilbash N, Collins R, Peto R. Body-mass index and cause-specific mortality in 900 000 adults: collaborative analyses of 57 prospective studies. Lancet. 2009 Mar 28;373(9669):1083-96. doi: 10.1016/S0140-6736(09)60318-4. Epub 2009 Mar 18. PMID: 19299006; PMCID: PMC2662372.
[3] Calle EE, Rodriguez C, Walker-Thurmond K, Thun MJ. Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults. N Engl J Med. 2003 Apr 24;348(17):1625-38. doi: 10.1056/NEJMoa021423. PMID: 12711737.
[4] Peeters A, Barendregt JJ, Willekens F, Mackenbach JP, Al Mamun A, Bonneux L; NEDCOM, the Netherlands Epidemiology and Demography Compression of Morbidity Research Group. Obesity in adulthood and its consequences for life expectancy: a life-table analysis. Ann Intern Med. 2003 Jan 7;138(1):24-32. doi: 10.7326/0003-4819-138-1-200301070-00008. PMID: 12513041.
[5] Adams TD, Gress RE, Smith SC, Halverson RC, Simper SC, Rosamond WD, Lamonte MJ, Stroup AM, Hunt SC. Long-term mortality after gastric bypass surgery. N Engl J Med. 2007 Aug 23;357(8):753-61. doi: 10.1056/NEJMoa066603. PMID: 17715409.
