The #1 Cause of Obesity, According to Science — Eat This Not That

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According to the CDC, more than 41% of American adults are obese, making obesity a serious public health crisis. "Americans are gaining weight, and obesity has become a national health threat," says J. Michael Gonzalez-Campoy, MD, PhD, FACE. "We can't place the problem purely on self-control. Why has obesity become such a weighty issue?" Here are the main causes of obesity, according to experts. Read on—and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had COVID.

More than a third of Americans are not getting enough sleep, with deeply concerning consequences for obesity and overall health. "Obesity develops when energy intake is greater than expenditure. Diet and physical activity play an important part in this, but an additional factor may be inadequate sleep," says Dr Kristen Knutson, from the University of Chicago. "A review of the evidence shows how short or poor quality sleep is linked to increased risk of obesity by de-regulating appetite, leading to increased energy consumption."

Researchers found that people with higher levels of cortisone in hair samples were more likely to be overweight. "These results provide consistent evidence that chronic stress is associated with higher levels of obesity," says Dr Sarah Jackson (UCL Epidemiology and Public Health). "People who had higher hair cortisol levels also tended to have larger waist measurements, which is important because carrying excess fat around the abdomen is a risk factor for heart disease, diabetes, and premature death."

Research from the University of São Paulo in Brazil found that adolescents who ate a diet high in ultra processed food were 45% more likely to develop obesity. "Generally speaking, ultra-processed food and drink contain chemical additives designed to make the products more appealing to the senses, such as colorants, emulsifiers and thickeners," says Daniela Neri, RD. "Many ultra-processed foods have high energy density and contain a great deal of sugar and fat, all of which contributes directly to weight gain. But even low-calorie products such as diet drinks can favor the development of obesity in ways that go beyond nutritional composition, such as by interfering with satiety signaling or modifying the gut microbiota."

"We spend too much time in front of a screen—a lot of time watching TV or in front of the computer—and this is especially true for children," says Dr. Gonzalez-Campoy. "Children between the ages of 8 and 18 years spend 7.5 hours each day engaging in entertainment media—TV, computers, cell phones, movies, and video games—and about 4.5 of these hours are devoted to watching TV. Not only do these passive pursuits detract from time that could be spent on physical activity, we eat meals and have snacks around the TV, which does its share of promoting this habit through advertising of high-calorie, unhealthful foods."

While 'calories in, calories out' is not the be-all-and-end-all of weight gain and weight loss, the amount of food we eat does count. "Your daily meals are like a bank account: you take in calories (income) and spend them on physical activity (expense)," says Dr. Gonzalez-Campoy. "When you take in more calories than you burn, you have a positive energy balance. While this would be a good thing for your bank account, it may not be a good thing for your weight. Of course, it is not simply a matter of addition and subtraction, and some people gain weight more readily than others."

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