What Causes Obesity?

Despite what many believe, the truth is that obesity is not simply a result of overeating and a lack of willpower. Scientific research shows that genetics also plays a role and studies have demonstrated that once obesity sets in, even the most concerted efforts to lose weight by dieting and exercising may not work.

While scientists continue to search for answers, the reality is that controlling your obesity will be a lifelong challenge. It’s important to understand that there is no cure for obesity and even a dramatic medical intervention such as weight loss surgery will require a sustained commitment.

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Watch this video for the Center for Weight Loss Surgery at Danbury Hospital “A lot of misconception surrounds the disease – and it is a disease.”

Dr. Keith Zuccala 

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Factors that Contribute to Obesity

Many factors contribute to the development of obesity including genetic, hereditary, environmental, metabolic and eating disorders. Some medical conditions, such as hypothyroidism, can result in obesity and some medications, such as steroids, can also cause dramatic weight gain.

Genetic Factors

Numerous scientific studies have established that your genes play an important role in your tendency to gain excess weight. For instance:

  • A study of body weight in adopted children shows no correlation with the weight of their adoptive parents, who feed them and teach them how to eat but meanwhile, had an 80% correlation with their biological (genetic) parents.
  • Identical twins, with the same genes, show a much higher similarity of body weights than do fraternal twins, who have different genes.
  • Certain groups of people, such as the Pima Indian tribe in Arizona, have a very high incidence of severe obesity – along with significantly higher rates of diabetes and heart disease -- than other ethnic groups.

It’s likely that we have a number of genes directly related to weight, perhaps affecting appetite, the ability to feel full or satisfied, metabolism, fat-storing ability, and even our natural activity levels.

The Pima Paradox

The Pima Indians are known in scientific circles as one of the heaviest groups of people in the world. In fact, National Institutes of Health researchers have been studying them for more than 35 years. Some adults weigh more than 500 pounds, and many obese teenagers are suffering from diabetes, the disease most frequently associated with obesity.

But here's a really interesting fact - a group of Pima Indians living in Sierra Madre, Mexico, does not have a problem with obesity and its related diseases. Why not?

The leading theory states that after many generations of living in the desert, often confronting famine, the most successful Pima were those with genes that helped them store as much fat as possible during times when food was available. Now those fat-storing genes work against them.

Though both populations consume a similar number of calories each day, the Mexican Pima still live much like their ancestors did. They put in 23 hours of physical labor each week and eat a traditional diet that's very low in fat. The Arizona Pima live like most other modern Americans, eating a diet consisting of around 40 percent fat and engaging in physical activity for only two hours a week.

The Pima apparently have a genetic predisposition to gain weight. And the environment in which they live - the environment in which most of us live - makes it nearly impossible for the Arizona Pima to maintain a normal, healthy body weight.

Environmental Factors

It’s not just genes, however. If you have a genetic predisposition toward obesity, the modern American lifestyle and environment make it even harder to control your weight. Fast food, long days sitting at a desk, and driving around our suburban world rather than walking magnify hereditary factors such as metabolism and efficient fat storage. Without changing some basic aspects of how they live, people who suffer from morbid obesity are rarely able to reach and maintain a healthy body weight.


We used to think of weight gain or loss as only a function of calories ingested and burned. Those who take in more calories than they burn gain weight, while those who burn more calories than they ingest lose weight. But now we know the equation isn't that simple.

Obesity researchers now talk about a theory called the "set point," a sort of thermostat in the brain that makes people resistant to either weight gain or loss. If you try to override the set point by drastically cutting your calorie intake, your brain responds by lowering metabolism and slowing activity. You then gain back any weight you lost.

Eating Disorders and Medical Conditions

Weight loss surgery is not a cure for conditions like hypothyroidism, nor will it resolve an eating disorder. If you have problems like these, you’ll need to work with your doctor to determine whether you need medication and/or counseling.

For More Information

If you think you may be a candidate for weight loss surgery, talk to your primary care physician about Danbury Hospital, call 1-800-516-3657 for more information, or attend a free event and learn more about losing weight through bariatric surgery and if it’s right for you.