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What Causes Obesity?

Contributor Fatima Cody Stanford, MD, MPH, MPA, MBA
7 minute read
An overweight man and woman jogging in the park.

An estimated 1 in 5 children and more than 1 in 3 adults struggle with the disease of obesity.

In this article, Fatima Cody Stanford, MD, MPH, MPA, MBA, explains the causes of obesity, its impacts on the body, and available treatment options. Dr. Stanford is a Mass General Brigham obesity medicine physician-scientist. She cares for patients at the Massachusetts General Hospital Weight Center and is also the equity director of the Endocrine Division at Mass General.

What is obesity?

“Obesity is a disease characterized by different signaling in the brain that tells your body how much to eat and how much to store,” explains Dr. Stanford. “There is a particular part of the brain that’s really responsible for weight regulation. That part of the brain is called the hypothalamus.”

So, if you've wondered, “Why do I struggle with my weight compared to my relatives and friends? What is it about me?” It's about how your brain signals and how that differs from someone else.

How do we screen for obesity?

Your doctor can calculate your body mass index (BMI) using a formula involving height and weight measurements. A higher number typically reflects a greater percentage of body fat. If you have a BMI over 30, you’re considered to be a person with obesity.

But BMI is not a perfect measure.

"BMI is not the end all be all," says Dr. Stanford. "When the charts and tables were developed, they were based upon metropolitan life insurance tables from the 1930s. They didn't include racial and ethnic minorities, so we use BMI with a grain of salt."

In addition to looking at BMI, your doctor might measure your waist circumference. “For females, we measure the waist circumference at the umbilicus, which is a fancy word for belly button,” explains Dr. Stanford. “We would use a tape measure. We're in a healthy zone if you are 35 inches or less. For men, it’s the same area… Our goal is to have a waist circumference of 40 inches or less.” Your doctor can help you figure out what a healthy weight range is for you.

Causes of obesity

"For many years, we supported this myth that it's all about calories in and calories out. And I'm here to dispel that myth. It's so much more complex," explains Dr. Stanford.

Many factors can play a role in how the body regulates weight. Contributors to obesity include:

  • Disordered eating, such as binge eating disorder

  • Genetic and epigenetic factors

  • Quitting smoking

  • Poor sleep

  • Gut microbiota

  • Physical disabilities

  • Family history of obesity in your mother or father

  • A sedentary lifestyle

It's also common for people to struggle with obesity due to age-related changes or other environmental factors. For example, people with a uterus (womb) share three common life experiences that can cause major weight shifts:

  1. First menstrual cycle as an adolescent

  2. Pregnancy (if they become pregnant)

  3. Menopause

The causes of childhood obesity are similar to the causes of obesity in adults. Typically, your risk of developing obesity increases if you grow up in a family with parents with overweight or obesity.

Other factors can include trauma history — increased stress can encourage your body to store fat. Limited access to affordable healthy foods also can cause major shifts in weight and weight status. Certain behaviors, like eating out a lot, can contribute as well.

There are those of us, particularly in obesity medicine, that are here to help you conquer and treat this disease. Recognize this is not your fault. We are here.

Fatima Cody Stanford, MD, MPH, MPA, MBA
Obesity Medicine Physician-Scientist
Mass General Brigham

Diseases linked to obesity

There are over 200 diseases associated with obesity. Some common conditions linked to obesity are:

Obesity and cardiovascular diseases commonly occur together. So do obesity and kidney disease. There's even a relationship between celiac disease and obesity. And we know of over 15 cancers related to or possibly triggered by the disease of obesity.

An overweight woman walks her pug in the park.

60 Minutes: Obesity as a disease

Dr. Stanford speaks with 60 Minutes about the importance of recognizing and treating obesity as a disease. “It’s a brain disease,” she says, explaining that obesity has little to do with willpower and is determined by what a person’s brain thinks their body needs.

Treatment for obesity

There are four potential treatment strategies for obesity:

  1. Lifestyle and behavioral therapies

  2. Medical devices

  3. Pharmacotherapy or medications

  4. Surgery

Lifestyle and behavior therapies

Lifestyle therapies focus on key factors, like eating healthy foods and staying active. Your therapist can help you enhance your diet by encouraging more lean proteins, whole grains, fruits, and vegetables. Behavioral therapies focus on mental health as it relates to obesity. They can help address any emotional factors that contribute to a person’s obesity diagnosis.

Medical devices

In addition to therapy, there's now also a device in the form of capsules that is approved for weight loss management by the U.S. Food and Drug Administration (FDA). Taken before food, the capsule expands to a jelly-like substance in your abdomen, helping you feel full. Eventually, your body moves the gel particles through the intestinal tract and excretes them.


Medication can also be used to treat obesity. There are several medications that are approved by the FDA ranging from pills to injections. Depending on the treatment, people may take these on a daily or weekly basis. Patients usually need to take these medications long-term.

In recent months, a concerning trend of people misusing drugs — particularly a medicine used to treat type 2 diabetes — has gained attention. It’s important to remember that all medications, including weight loss medications, should only be used as directed under the supervision of a doctor.

Weight loss surgery

Doctors may recommend weight loss surgery to people with moderate to severe obesity or with an obesity-related disease like obstructive apnea, type 2 diabetes, or a related heart condition.

"Metabolic and bariatric surgery leads to an 89% improvement in life expectancy within the course of 5 years," says Dr. Stanford."

And most patients report that their quality of life improves within just 3 to 6 months after surgery.

Surgery can also help manage conditions associated with obesity, including:

  • Sleep apnea

  • High cholesterol

  • Asthma

  • High blood pressure

  • Fatty liver disease

  • Metabolic syndrome

  • Acid reflux

  • Type 2 diabetes

  • PCOS

If you or anyone you love has struggled with weight, please know that you are not alone. Obesity is the most prevalent chronic disease of our time, and there is hope.

“There are those of us, particularly in obesity medicine, that are here to help you conquer and treat this disease,” says Dr. Stanford. “Recognize this is not your fault. We are here.”


Obesity Medicine Physician-Scientist