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The #1 Reason People Get Obese, According to Science

Be aware of this leading factor.
FACT CHECKED BY Emilia Paluszek

What is the number one reason people get obese, according to science?

Emily Rubin, RD, LDN, Director of Clinical Dietetics Celiac Center, Fatty Liver Center, Weight Management Center at Thomas Jefferson University, explains. "Two different patients come into my office," she says. "They live in different zip codes, are the same age and sex and eat a similar number of calories each day. Why does one patient weight 150 pounds and the other weigh 250 pounds? Read on to find out more—and to ensure your health and the health of others, don't miss these Sure Signs You May Have Already Had COVID.


What is Obesity?

Man with hand on his stomach to depict indigestion

Obesity is a complex health issue—a disease resulting from a combination of factors, including behavioral, community environment, and genetics—all of which reflect your zip code. Where you live determines your risk for obesity. Behaviors are based on physical activity and dietary patterns in the community environment, like having access to grocery stores and safe areas to exercise. Tack on the genetics, the predisposition or family history for developing obesity and living in a specific zip code, will then determine how people respond to physical inactivity and intake of high-calorie foods." Read on to learn the leading factors of obesity.


Why Do People Get Obese?

Nutritionist with young woman client talking about meal plan and healthy products during a medical consultation in the office

 "There's not one simple reason people get obese," agrees Samantha Cassetty, MS, RD, NYC-based nutrition and wellness expert and co-author of Sugar Shock. As a weight management specialist, she's seen clients who struggle with obesity, which WHO defines "as abnormal or excessive fat accumulation that presents a risk to health. A body mass index (BMI) over 25 is considered overweight, and over 30 is obese." Adds WHO: "The issue has grown to epidemic proportions, with over 4 million people dying each year as a result of being overweight or obese."

"There are so many factors, including access to healthcare; availability of safe places to participate in physical activity; ability and time to prep and cook, and access to whole foods," says Cassetty. However, there is one leading factor, she says, that leads people to become obese.

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The Leading Factor of Obesity is Our Food Environment

woman in furry sweater reaching into clear glass bowl to grab potato chip while laptop sits in background
Shutterstock / Olha Pylypenko

"A leading factor is that our food environment promotes heavily processed foods that get digested quickly and leave you hungry soon after eating," says Cassetty. "There's also evidence that heavily processed foods may disrupt signals to the brain that tell you when you're full, so in many ways, they contribute to overeating. On top of that, when you eat ultra-processed foods, your brain tells you they're really rewarding, so it reinforces your desire to want to continue to eat them. Fast food, chips, pizza, ice cream, and the like are all considered heavily processed foods. These foods contain refined grains and may be high in sugar, salt, or both. Added sugars and refined grains promote inflammation, which is an underlying factor in the development of many health problems, including obesity. So, the convenience and affordability of heavily processed foods are important factors in the development of obesity." (For her sources of this intel, see here, here, here and here.)

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Avoid Highly Processed Foods

Hands holding fresh delicious burgers with french fries, sauce and beer on the wooden table top view.

Melissa Mitri, MS, RDN, Owner of Melissa Mitri Nutrition, LLC, agrees. "Highly processed foods," she says when asked about the #1 cause of obesity. "Processed foods that come in a package are linked to excess weight gain. Research has shown that those who consume more processed foods tend to weigh more. This is because these foods are designed to be highly palatable and addicting. Processed foods are also not as filling, so they are easier to overeat." 

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Here's What to Eat Instead

healthy foods

So what to eat instead? "Choosing more whole foods that don't come in a package helps to support a healthy weight," says Mitri. Obese or not, challenge yourself to take one full day where you eat nothing processed—just whole grains, lean proteins and healthy fats, that come from the Earth. Then try it for two days, or three. For inspiration, try any of these 19 Weight Loss Foods That Really Work, Say Experts.


How To Tell if You're Becoming Obese, First Calculate Your BMI, Says the CDC

BMI calculation

First, assess your Body Mass Index. "BMI and waist circumference are two screening tools to estimate weight status and potential disease risk," says the CDC. "BMI is a person's weight in kilograms divided by the square of height in meters.

  • If your BMI is less than 18.5, it falls within the underweight range.
  • If your BMI is 18.5 to 24.9, it falls within the normal or Healthy Weight range.
  • If your BMI is 25.0 to 29.9, it falls within the overweight range.
  • If your BMI is 30.0 or higher, it falls within the obese range."

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To Tell if You're at Greater Risk, Measure Your Waist

Doctor measuring obese man waist body fat.

"Another way to estimate your potential disease risk is to measure your waist circumference," says the CDC. "Excessive abdominal fat may be serious because it places you at greater risk for developing obesity-related conditions, such as Type 2 Diabetes, high blood pressure, and coronary artery disease. Your waistline may be telling you that you have a higher risk of developing obesity-related conditions if you are:

  • A man whose waist circumference is more than 40 inches
  • A non-pregnant woman whose waist circumference is more than 35 inches.

To correctly measure waist circumference:

  • Stand and place a tape measure around your middle, just above your hipbones
  • Make sure tape is horizontal around the waist
  • Keep the tape snug around the waist, but not compressing the skin
  • Measure your waist just after you breathe out."

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Obesity Affects These Groups More Than Others—See if You're Included

Obese man measuring his waist.

Not everyone is as afflicted with obesity as others. "Non-Hispanic Black adults (49.6%) had the highest age-adjusted prevalence of obesity, followed by Hispanic adults (44.8%), non-Hispanic White adults (42.2%) and non-Hispanic Asian adults (17.4%)," says CDC. "The prevalence of obesity was 40.0% among adults aged 20 to 39 years, 44.8% among adults aged 40 to 59 years, and 42.8% among adults aged 60 and older."


What to Do if You Worry You're Becoming Obese

Woman doing butt squats

"The key to achieving and maintaining a healthy weight isn't short-term dietary changes; it's about a lifestyle that includes healthy eating and regular physical activity," says the CDC. "Choosing a lifestyle that includes good eating habits and daily physical activity can help you maintain a healthy weight and prevent weight gain."

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Take Back Your Health


Remember, this isn't just about your weight. "Obesity is a contributing cause of many other health problems, including heart disease, stroke, diabetes, and some types of cancer," says the CDC. "These are some of the leading causes of death in the U.S. Obesity can cause sleep apnea and breathing problems and make activity more difficult. Obesity can also cause problems during pregnancy or make it more difficult for a woman to become pregnant.". And since obesity can lead to severe COVID-19, get vaccinated when it becomes available to you, and to protect your life and the lives of others, don't visit any of these 35 Places You're Most Likely to Catch COVID.

Alek Korab
Alek Korab is a Co-Founder and Managing Editor of the ETNT Health channel on Eat This, Not That! Read more about Alek
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