What is Obesity

What Is Obesity?

Between 1999 and 2018, the prevalence of obesity in the USA increased from 30.5% to 42.4%. Being obese may cause self-consciousness and low self-esteem.

However, it also strongly correlates with numerous physical health complications, including type 2 diabetes, stroke, cardiovascular diseases, and some cancers.

In this article, we will look in more detail at the causes of obesity, its associated risks, and the obesity treatment options currently available.

How Do You Define Obesity?

Obesity can be defined as having a Body Mass Index of 30 or higher. Less commonly, waist circumference is used to screen for obesity.

Body Mass Index (BMI)

Your Body Mass Index is calculated by comparing weight and height to see whether the two are in proportion. If your body weight is proportionately greater than your height, you may be classed as overweight or obese. Conversely, if your weight is proportionately lower than it should be for your height, you might be underweight.

The following calculation will give you your BMI.

  • Weight in kilograms ÷ Height in metres2 = BMI
  • For example: 65 kilograms ÷ (1.65m x 1.65m) = 23.88

The following table shows the weight classes for adults aged 20 or older in the USA.

18.5 to <25Healthy weight
25.0 to <30Overweight
30.0 or higherObese

The BMI in the above example would therefore put someone in the healthy weight category.

For a BMI of 30 or higher, the CDC has defined three further classes of obesity.

30 to <35Class 1 obesity
35 to <40Class 2 obesity
40 or higherClass 3 (also known as morbid obesity, extreme obesity, or severe obesity)

The classifications for childhood obesity are different as a child’s body composition changes with age, with variation between boys and girls. A child can, therefore, only be categorized as overweight or obese in comparison to the average BMI for other children of the same age and sex.

Waist Circumference

Scientific evidence has proven that waist circumference is an accurate predictor of weight-related morbidity. The risk of certain weight-related illnesses increases when abdominal obesity (measured by waist circumference) is present when compared to those with a smaller waist ( 4 ). Waist circumference is, therefore, another tool used to diagnose obesity.

A higher waist circumference increases the risk of high blood pressure, other cardiovascular diseases, type 2 diabetes, high cholesterol, and joint pains. It is even associated with an increased risk of death ( 4 , 5 ).

The CDC estimates that the risk of obesity-related complications is increased for men with a waist circumference of over 40 inches and non-pregnant women whose waist circumference is greater than 35 inches ( 6 ).

What Causes Obesity?

In essence, overweight and obesity occur when more calories are consumed than expended long term. Weight gain occurs because the excess calories that are not used for energy during everyday activities or exercise are instead stored as body fat.

Generally, the more sedentary your lifestyle, the fewer calories you will burn each day. Conversely, someone with a more active lifestyle will likely be able to eat more calories each day without experiencing weight gain.

Risk Factors for Obesity

Risk Factors

Sometimes, obesity is caused by more complex factors than simply over-eating. In general, there are four risk factors:

  • Race
  • Education
  • Health Conditions
  • Environment

In the following, we will be looking at each one of the risk factors in detail.


In the US, Non-Hispanic Black adults are at the greatest risk of obesity, with 49.6% being classified in this category in 2017-2018. By comparison, only 17.4% of non-Hispanic Asian adults were classed as obese.


Overall, men and women with college degrees were less likely to be obese than those who stopped education earlier.

In some races and ethnicities, obesity risks may increase or decrease depending on education and income group. For example, in non-Hispanic White women, obesity was less common in the highest-income group when compared to middle and low-earners.

Health Conditions

Some health conditions can increase your risk of weight gain. Often, the weight gain occurs because the condition increases the propensity to overeat or reduces the ability to exercise. Reassuringly, appropriate treatment of the underlying condition may help you to lose weight.

Medical conditions that may increase your risk of weight gain include:

  • Arthritis that reduces mobility or makes it harder to exercise
  • Hypothyroidism (underactive thyroid)
  • Genetic conditions, including Prader-Willi syndrome
  • Cushing syndrome
  • Polycystic ovary syndrome (PCOS) ( 7 ).

Some prescription medications can also increase the risk of weight gain.


Feeling stressed or sleeping badly can both increase the likelihood of weight gain. Over-eating is common at times of emotional upset, and poor sleep can affect the body’s regulation of energy expenditure and appetite.

Oversized portions, lack of open space for exercise, and not being able to afford healthier foods can also make obesity more likely ( 7 ).

Complications of Obesity

Complications Obesity

When talking about obesity, it is short-sighted to focus on the simple definition of excess weight. Because of the associated health complications, the yearly medical costs for individuals with obesity is around $1,429 more than for those in a healthy weight bracket.

It is important to be aware of the symptoms or signs that may occur if obesity complications develop, so that appropriate investigation and treatment can be instigated.

High Blood Pressure

High blood pressure, or hypertension, causes increased pressure in the cardiovascular system.

It is often associated with high cholesterol levels and fatty deposits within the vessels, increasing the strain on the heart. Hypertension often occurs without symptoms, but as it can increase the risk of heart attacks or a stroke, it is important that your doctor checks your blood pressure regularly. Treatment can then be started if required.

Type 2 Diabetes

Weight-related diabetes occurs when the pancreas produces less insulin, a hormone that lowers blood sugar levels. The body also becomes resistant to any insulin that is still produced. With little circulating insulin, blood sugar levels increase.

The symptoms of persistently high blood sugar levels include passing urine more than usual, feeling thirsty, and increased tiredness. However, some people will not notice any symptoms.

Diabetes can increase the risk of damage to organs, including the eyes, kidneys, heart, and brain.

Regular reviews of your blood sugar level will ensure a diagnosis of diabetes is not missed. If your levels are high, treatment with a tablet of medication or insulin may be required.


Damage to the bones and joints is more likely if your skeletal system is supporting excess weight. Early-onset ‘wear and tear’ arthritis (osteoarthritis) can particularly affect the knees and hips. Pain in these joints can severely restrict the amount of exercise you do, leading to a vicious cycle of inactivity and further weight gain.


There is significant evidence that a higher proportion of body fat increases the risk of certain cancers, including, but not limited to, cancer of the:

  • Endometrium (lining of the uterus)
  • Esophagus (food pipe)
  • Stomach
  • Liver
  • Kidneys
  • Meninges (membrane of the brain)
  • Pancreas
  • Bowel ( 8 ).

If you are concerned about any new symptoms, it is important to seek advice from your doctor.

Obesity Treatment

Medical Treatment of Obesity

Losing weight is often considered a difficult task. Successful weight loss requires willpower and determination. Many people, therefore, seek treatment to help them lose weight.

Obesity treatments fall into one of three categories: lifestyle modification (diet and exercise), medical treatment, or surgical management.

Lifestyle Modifications

An important part of preventing weight gain and attaining a healthy weight is making appropriate lifestyle changes.

When patients decide to change their eating habits, they should focus on improving their health rather than losing weight. The following tactics can help:

  • Eat nutritiously
  • Set clear, quantifiable, and achievable goals
  • Manage emotions, in particular, stress
  • Increase cardiorespiratory and muscular fitness
  • Drink a lot of water

 You can learn more in our article on how to lose weight.

Weight Loss Medications

Numerous medications are available to aid weight loss, with several different mechanisms of action. Weight loss medications may:

  • Reduce the appetite
  • Increase feelings of fullness
  • Prevent fat absorption
  • Increase central nervous system activity.

Taking a prescription weight loss medication can improve the chance of significant weight loss (around 10% of the baseline weight), but side effects may occur ( 9 ).

Some people choose natural over-the-counter weight loss medications such as PhenQ to avoid side effects.

Surgical Management

Bariatric surgery has been shown to consistently aid weight loss. Gastric bypass surgery reduces the functional volume of the stomach, making it uncomfortable to eat large amounts. This can lead to dramatic, sustained weight loss.

Those with morbid obesity (A BMI of 40 or above) are generally considered candidates for this type of surgery ( 12 ).


The prevalence of obesity is rising in the USA. Being obese is linked to an increased risk of serious long-term medical complications, including heart disease, diabetes, and arthritis. Obesity is also a cause of premature death.

Although the treatment of obesity-related complications is vital, some people also seek medical or surgical treatment to help them lose weight. Treatment ranges from lifestyle changes to prescription medications or even bariatric surgery.

If you are ready to begin losing weight naturally, you can find out more about PhenQ here.


1. Centers for Disease Control and Prevention. Adult Obesity Facts.
2. Centers for Disease Control and Prevention. Adult Body Mass Index.
3. Centers for Disease Control and Prevention. Defining Child BMI Categories.
4. Ross R, Neeland IJ, Yamashita S, Shai I, Seidell J, Magni P, Santos RD, Arsenault B, Cuevas A, Hu FB, Griffin BA, Zambon A, Barter P, Fruchart JC, Eckel RH, Matsuzawa Y, Després JP. Waist circumference as a vital sign in clinical practice: a Consensus Statement from the IAS and ICCR Working Group on Visceral Obesity. Nat Rev Endocrinol. 2020 Mar;16(3):177-189. doi: 10.1038/s41574-019-0310-7. Epub 2020 Feb 4. PMID: 32020062; PMCID: PMC7027970.
5. Darsini D, Hamidah H, Notobroto HB, Cahyono EA. Health risks associated with high waist circumference: A systematic review. J Public Health Res. 2020 Jul 2;9(2):1811. doi: 10.4081/jphr.2020.1811. PMID: 32728557; PMCID: PMC7376462.
6. Centers for Disease Control and Prevention. Assessing Your Weight.
7. National Institute of Child Health and Human Development. What causes obesity & overweight?
8. National Cancer Institute. Obesity and Cancer.
9. National Institute of Diabetes and Digestive and Kidney Diseases. Prescription Medications to Treat Overweight & Obesity.
10. Phentermine.com (2023).
11. Torres-Landa S, Kannan U, Guajardo I, Pickett-Blakely OE, Dempsey DT, Williams NN, Dumon KR. Surgical management of obesity. Minerva Chir. 2018 Feb;73(1):41-54. doi: 10.23736/S0026-4733.17.07588-5. Epub 2017 Dec 14. PMID: 29243457.
12. University of Pittsburgh Medical Centre. Defining Obesity.