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The #1 Cause of Obesity, Says Science

What causes obesity—and what to do about it.
FACT CHECKED BY Emilia Paluszek

Obesity is the leading preventable cause of death in the U.S. and linked to life-threatening conditions including type 2 diabetes, heart disease, and cancer. "Americans are gaining weight, and obesity has become a national health threat. We can't place the problem purely on self-control. Why has obesity become such a weighty issue?" says J. Michael Gonzalez-Campoy, MD, PhD, FACE. Here are the main causes of obesity, according to doctors. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.


Obesity and COVID-19

Doctor talking with an obese woman and measuring her.

Research shows that obesity is linked to a higher risk of being hospitalized with COVID-19 complications—but losing weight can significantly lower that risk. "The research findings show that patients with obesity who achieved substantial and sustained weight loss with bariatric surgery prior to a COVID-19 infection reduced their risk of developing severe illness by 60 percent," says Ali Aminian, M.D., director of Cleveland Clinic's Bariatric & Metabolic Institute. "Our study provides strong evidence that obesity is a modifiable risk factor for COVID-19 that can be improved through a successful weight-loss intervention."


Sedentary Lifestyle

overweight woman at home lying on the floor, laptop in front of her, prepared to work out on mat according to video

Studies show that living a sedentary lifestyle with limited exercise is linked to a higher risk for obesity—which is why it's important to ensure people have access to safe spaces for working out, even just taking a walk. "There are societal and economic forces at work that we must address," says Pamela Powers Hannley, MPH. "Take, for example, the struggle of single mothers who are trying to balance work and child care. They may lack the time or resources to exercise. We shouldn't assume that people are just lazy. Their lives might be overwhelming to them. It's going to take widespread change. We shouldn't just tell patients they need to work out. We need to work with communities, employers and local governments to enable healthy lifestyles by ensuring that there are safe spaces to exercise that are cheap or free."


Bad (Or Not Enough) Sleep

young woman having a panic attack
Shutterstock / fizkes

The CDC recommends adults get at least seven hours of sleep every night, yet a third of Americans are not getting enough sleep—and it's contributing to the obesity epidemic. "The possibility that sleep – the most sedentary activity of all – contributes to the obesity epidemic is gaining recognition in the scientific community," says Jean-Philippe Chaput, Ph.D. "On a hormonal level, lack of sleep may disrupt a number of hormones that affect our drive to eat. Less time spent sleeping also means more time and opportunities for eating. Lack of sleep has been shown to increase snacking, the number of meals eaten per day, and the preference for energy-dense foods. Increased food intake associated with a lack of sleep can also be seen as a normal physiological adaptation to provide energy needed to sustain additional wakefulness. On the other side of the energy balance equation, sleep loss generally leads to a general feeling of fatigue, which can make us feel less inclined to want to do physical activity."  
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Mature businessman experiencing a headache while working at his desk

Chronic stress can unleash hormones that trigger overeating, studies show. "When people are facing a stressful situation, a chain reaction is set off in the body that results in the release of cortisol, leading to higher levels of this hormone in the body," says Sarah Jackson, Ph.D. "Cortisol is involved in a broad range of biological processes, including metabolism, body composition and the accumulation of body fat. When we're stressed out we may also find it more difficult to find the motivation to go for a run or resist unhealthy foods."

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The #1 Cause of Obesity Is…

Man eating pizza having a takeaway at home relaxing resting

The number one reason people are overweight is they eat too much, and specifically too much of the wrong types of foods: Experts believe excess sugar and overly-processed carbohydrates are fuelling the obesity epidemic. "Rather than solely treating the symptoms of obesity and related diseases with medication, we need to include efforts to use food as medicine," says Leigh A. Frame, PhD, MHS. "Chronic disease in later years is not predestined, but heavily influenced by lifestyle and diet. Decreasing obesity and chronic disease in the U.S. will require limiting processed foods and increasing intake of whole vegetables, legumes, nuts, fruits, and water. Health care providers must also emphasize lifestyle medicine, moving beyond 'a pill for an ill.'"

RELATED: Habits Secretly Increasing Your Abdominal Fat, Say Physicians

Ferozan Mast
Ferozan Mast is a science, health and wellness writer with a passion for making science and research-backed information accessible to a general audience. Read more about Ferozan
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