The Big Picture: Overweight and Obesity -

Kaitlin Little

Overweight and obesity in the United States is a serious public health concern. According to the latest report from the Centers for Disease Control & Prevention (CDC), obesity rates among both American adults and children have continued to rise over the last decade.

The percentage of adults with a BMI classifying them as obese grew from 34% in 2007-08 to nearly 40% in 2015-16, marking the nation’s record high. Just thirty years ago, no state had an obesity rate above 15%. [1]

Alarmingly, the trend is not confined to adults. Young Americans have been piling on the pounds too, with nearly 19% of the nation’s youth (aged 2 to 19 years) currently considered obese. [1] The rise in childhood obesity is most concerning, considering that overweight and obese children tend to stay obese into adulthood and are more likely to develop a chronic disease at a younger age. [2]

The latest statistics on obesity are clearly bleak. But, these figures are part of a far bigger problem as today, 7 in 10 Americans are either overweight or obese, making people within a normal weight range the minority.

The repercussions of this epidemic are severe and include an increased risk of heart disease, stroke, type II diabetes, and certain cancers.

What is Overweight and Obesity?

The World Health Organization (WHO) defines overweight and obesity as an “abnormal or excessive fat accumulation that may impair health”.

Body Mass Index (BMI), although not a perfect indicator, is commonly used to classify people as overweight or obese. It is a simple measurement of an individual’s weight relative to their height and provides an indication of total body fat. You can calculate your BMI by dividing your weight in kilograms by the square of your height in meters (kg/m²).

In adults, a BMI of 18.5-24.9 is normal, a BMI of 25–29.9 is considered overweight, and a BMI equal to or greater than 30 is considered obese.

In children, BMI is measured against WHO growth reference charts. A BMI greater than one standard deviation above the average BMI for age is considered overweight, while a BMI greater than two standard deviations above the average BMI for age is considered obese.

What Causes Weight Gain and Obesity?

At first glance, the cause of obesity seems simple: If you consume more calories than you expend through physical activity, you will gain weight. But, as with many health issues, the explanation is not that straightforward.

Looking below the surface, we can see that being overweight or obese is the result of a complex interplay between genetic, behavioral, environmental, and socioeconomic factors, all of which lead to an imbalance between energy intake and energy expenditure over time.

Genetics

Obesity has a strong genetic component, with researchers identifying over 60 genetic markers that increase one’s susceptibility to gaining weight. [3] Some research has even suggested that children with obese parents are 25% more likely to be overweight. However, that doesn’t mean obesity is entirely predetermined. The food you eat has a large impact on the genes that are expressed and those that are not, as evidenced by studies on identical twins. [4]

Genetics alone cannot account for the disproportionate increase in obesity seen in developing countries over the last century. Hence, researchers are now investigating a gene-environment interaction, founded on the theory that underlying genetics predispose an individual to certain obesity-causing behaviors.

Behavioral

An individual’s behavior is perhaps the most significant, and a most modifiable, risk factor for overweight and obesity. Over-consumption, in addition to increasingly sedentary lifestyles, are primary contributors to the overweight problem. More and more Americans are consuming a diet high in heavily-processed, energy-dense foods loaded with sugar and saturated fats that fuel our appetite and expand our waistline. Furthermore, only 23% of Americans currently meet national physical activity guidelines. [5] It is recommended that adults get at least 150 minutes of moderately intense exercise each week, as well as muscle strengthening exercise at least twice a week.

Environment

As a society, our increase in caloric intake and a concomitant drop in energy expenditure can be attributed to the “obesogenic” environment that promotes physical inactivity and poor dietary choices. Industrialization and urbanization in the United States over the last five decades has made high-fat and high-sugar foods readily available and more affordable than ever. Coupled with aggressive marketing, food manufacturers have engineered products to be cheap, last long on the shelf and taste so good that they are near impossible to refuse. These junk foods also stimulate reward centers in the brain and can trigger food addiction in susceptible individuals. Researchers have shown that regularly bingeing on sugar stimulates the releases of a “feel good” chemical dopamine in the brain, much the same as addictive drugs. [6] [7]

The steady decline in physical activity levels can be attributed to an increased reliance on motorized transportation. Currently, over 76% of Americans drive to work, while just 3.3% walk or cycle. [8] Furthermore, with a tendency toward office jobs and advances in technology, work is far less physically demanding than it once was. [9]

Socioeconomic

An individual’s education, income level, gender, and ethnicity have a complex link to the development of overweight or obesity. According to data collected from the 2011–2014 National Health and Nutrition Examination Survey (NHANES), the prevalence of obesity is higher in less educated men and women, compared to those with a college degree. In females, obesity and overweight is highest among low-income earners. However, in males, middle-income earners are more likely to be overweight and obese. The overall prevalence of obesity is highest among Hispanic and non-Hispanic black adults and youths, when compared to other ethnicities. Women, in general, have a higher prevalence of obesity than men in most ethnicities, except non-Hispanic white adults. [10]

What are the Consequences of Overweight and Obesity?

Overweight and obesity has grave health consequences and places a heavy burden on the economy and society. Each year the disease costs American taxpayers over 150 billion dollars and causes an estimated 300,000 premature deaths. [11] People who are overweight or obese have a much greater risk of developing a serious health condition, including, but not limited to, the following:

Type II Diabetes

The term “diabesity” has been formed to describe the pressing correlation between Type II Diabetes and obesity. In fact, the risk of developing the condition increases by 20% for each 1 kg/m2 increase in BMI. [12] Type II Diabetes develops when the body’s cells no longer respond to insulin, and/or the pancreas gradually loses the ability to produce sufficient insulin resulting in elevated blood glucose (sugar) levels which can lead to a host of medical problems.

Elevated levels of free fatty acids in overweight and obese individuals induces oxidative stress and increases inflammation, which leads to insulin resistance. Furthermore, continually consuming in excess leads to chronically high blood glucose levels, which places stress on the pancreas and over time hinders its ability to produce insulin.

Hypertension

Individuals who are overweight or have obesity generally have high blood pressure, which is how hard blood pushes against the walls of the arteries. Increased abdominal fat, in particular, accounts for a 54% to 75% increase in the risk for hypertension.[13]

Hypertension is common in obese individuals, as the heart must pump harder to force blood around a larger body. Increased adipose (fat) tissue can also physically compress the kidneys and cause hormonal imbalances within the system that regulates blood pressure and fluid balance.

Coronary Heart Disease and Ischemic Stroke

Overweight and obese individuals are at an increased risk of suffering a stroke or heart attack. For example, a 25-year-long prospective study found that women who became overweight or obese with a BMI above 27 had approximately 42% higher risk of having a stroke than those who remained within a healthy weight range. [14]

The higher prevalence of heart disease and stroke among overweight and obese individuals is primarily due to hypertension, elevated levels of LDL cholesterol, and accelerated atherosclerosis (narrowing of arteries due to the build-up of fatty plaques).

Cancer

Overconsumption has been described as the “oil that fuels the flame” of cancer. Recent research into the link has revealed that some 14-20% of cancer deaths are due to obesity, and has implicated overweight and obesity in colorectal, pancreatic, breast, and ovarian cancer. [15]

Continually overeating causes a systemic increase in free-fatty acids, insulin, glucose, inflammatory cytokines, and the hunger inhibiting hormone leptin. These imbalances can directly promote the survival of cancer cells. [16]

Infertility

Overweight and obesity is associated with an increased risk of infertility and miscarriage. [17] In females, excess adipose tissue appears to affect ovulation and additional free fatty acids within the blood lead to chronic low-grade inflammation that affects reproductive organs. In males, increased inflammation disrupts testosterone needed for sperm production, and can cause fragmentation of sperm DNA. [18]

Osteoarthritis

Being overweight or obese is a risk factor for osteoarthritis, a progressive condition that affects the bones and cartilage of joints. It is a leading cause of joint pain and disability in the United States.

Carrying extra bodyweight places greater stress on the lower limbs, leading to joint inflammation, cartilage damage and deterioration of ligaments. For this reason, overweight and obese individuals are much more likely to require a knee replacement. [19]

Sleep Apnea

Excess weight is the biggest risk factor for sleep apnea, a condition that causes a person to have one or more pauses in breathing during sleep. The condition is present in approximately 40% of obese individuals, and approximately 70% of people with sleep apnea are obese. [20]

Excess fat stored around the neck can make the airway smaller, causing snoring and making it more difficult to breathe at night. If left untreated, sleep apnea can lead to poor sleep quality and chronic fatigue that negatively impacts day-to-day life. Sleep apnea can also be associated with hypertension and other cardiovascular diseases.

Mental Health Disorders

There is a strong and complex link between obesity and mental health disorders, including depression, eating disorders and attention deficit hyperactivity disorder (ADHD). [21] A history of mental illness can increase the risk of obesity while having obesity can make an individual more likely to develop a psychiatric disorder. According to longitudinal studies, obese adolescents have a 70% greater risk of depression, and obese women have a 38% higher risk of depression. Unsurprisingly, feeling dissatisfied with one’s body, in combination with societal pressures, can severely affect self-esteem and contribute to anxiety and depression.

Overweight and Obesity is Preventable

Being overweight or obese can have a profound impact on a person’s quality of life and their lifespan. If the prevalence continues to rise at the current rate, it has been predicted that over 86% of adults will be overweight or obese by 2030. [22] However, through lifestyle changes, including regular physical activity and a healthy balanced diet, overweight and obesity can often be prevented, or at the very least, managed.

References

[1] https://www.cdc.gov/nchs/data/databriefs/db288.pdf

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4408699/

[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4859313/

[4] https://www.ncbi.nlm.nih.gov/pubmed/2336074

[5] https://www.cdc.gov/nchs/data/nhsr/nhsr112.pdf

[6] https://www.sciencedirect.com/science/article/abs/pii/S0306452205004288

[7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2235907/

[8] https://www.cdc.gov/pcd/issues/2016/16_0181.htm

[9] https://www.ncbi.nlm.nih.gov/pubmed/15760296

[10] https://www.cdc.gov/obesity/data/adult.html

[11] https://www.healthaffairs.org/doi/10.1377/hlthaff.28.5.w822

[12] https://www.ncbi.nlm.nih.gov/pubmed/16611666/

[13] https://www.ahajournals.org/doi/full/10.1161/CIRCRESAHA.116.305697

[14] https://www.ncbi.nlm.nih.gov/pubmed/9153368/

[15] https://www.nejm.org/doi/full/10.1056/NEJMoa021423

[16] https://www.sciencedirect.com/science/article/pii/S1550413115006300

[17] https://www.sciencedirect.com/science/article/pii/S0015028217300602

[18]https://journals.lww.com/co-urology/Abstract/2017/09000/Obesity_and_male_infertility.8.aspx

[19] https://www.sciencedirect.com/science/article/pii/S0378512216300779

[20] https://www.ahajournals.org/doi/full/10.1161/01.HYP.0000101686.98973.A3

[21] https://psycnet.apa.org/record/2004-21949-007

[22] https://www.ncbi.nlm.nih.gov/pubmed/18719634/

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