Obesity in the U.S. isn’t going away anytime soon, according to new data from the National Health and Nutrition Examination Survey. Nearly 40% of adults and more than 17% of youth in the U.S. were obese between 2013 and 2014; 10 years before, about 32% of adults and 17% of youth (the same as last year) were obese.

Although the new data didn't represent a statistically significant increase from the last time the survey was conducted, from 2011 to 2012, it shows obesity remains prevalent among both adults and children, despite recent efforts to fight the issue. “I was surprised. I was not expecting this,” said Bartolome Burguera, an endocrinologist at Cleveland Clinic’s Endocrinology and Metabolism Institute. “It’s a very important wake-up call.”

The Centers for Disease Control and Prevention define obesity in terms of body-mass index (BMI). Those with a BMI of 30 or higher are considered obese. Experts said the survey’s results indicate that many factors are contributing to Americans’ obesity, and they don’t all have to do with food.

In fact, there have been some positive signs that Americans are changing the way they eat. American adults and children slightly decreased the amount of calories they were consuming on a daily basis from 2003 through 2004 to 2009 through 2010, according to separate research from Shu Wen Ng, Meghan M. Slining and Barry M. Popkin.

The researchers concluded that these changes in energy intake were independent from economic conditions or food prices, and public health efforts were likely to have helped.

Soda consumption in the U.S. has also dropped dramatically.

A newer study from Cornell also found that consuming specific high-calorie or high-sugar foods isn’t related to BMI in 95% of the population; in fact, morbidly obese people actually eat fewer sweet and salty snacks than average-weight individuals, though they do eat more french fries. They concluded that overall diet, including calories from grains, oils and dairy fats, combined with physical exercise and portion control, mattered much more than targeting specific foods. (And, to be clear, that doesn’t mean gorging on junk food won’t make you overweight.)

Still, despite recent findings, there is still work to be done about the foods Americans eat.

Larger portion sizes for adults and children, plus the amount of sugar in Americans’ diets, remain a concern, especially due to the prevalence of savory items that aren’t well-known for their sugar content, including such items as fast-food cheeseburgers and certain salad dressings, said Christopher Ochner, a weight loss and nutrition expert at Mount Sinai Hospital.

Beyond food, there are several other factors at play. Here are 5:

1. Exercise

Americans are much more sedentary than in the past, Burguera said; a lot of people go an entire day without burning many calories. “You don’t even have to get up to go to a meeting. You just have a meeting through the Internet,” Burguera said. “Before you get home, you stop at a drive-through restaurant, then you continue to answer emails from your bed.”

In fact, less than half of adults met federal guidelines for physical activity in 2014, with white adults slightly outperforming those who are black and Hispanic.

Better transportation options also mean Americans walk less than in the past, said Holly Lofton, the director of the weight management program at NYU’s Langone Center.

And more children play sedentary games. In the past they would be “playing things like dodgeball, and they’re playing on an iPad now,” she said.

Still, simply increasing exercise isn’t a cure-all, Ochner said, since those who exercise often then compensate by consuming extra calories.

2. Income

Americans in some lower-income demographics struggle more with obesity because consistently eating healthy and fresh foods can be more expensive than fast food or packaged foods, Ochner said.

Living far from locations that sell produce and other healthier foods — in areas known as “food deserts” — also contributes, Lofton said.

More than 23 million Americans live in these areas, according to the United States Department of Agriculture.

Plus, cooking a meal takes time. “When you have a very busy schedule, and when you have other important social and financial problems, eating right probably becomes a secondary point,” Burguera said.

Those with lower incomes also may have less information about healthy eating, as well as less access to care for issues related to being overweight. People who don’t have health insurance often can’t afford to see a medical weight-loss specialist, Lofton said. They may also be unable to consistently exercise, whether that’s for lack of money for a gym membership, or lack of time or a safe outdoor space.

3. Stress

Longer work hours and greater competition, both at work and academically, contribute to stress and consequently, weight gain. When people experience stress, the body feels a flight-or-fight response; this makes the body more hungry, so it will have the energy to fight off the attack, and it could lead to the body storing more fat, Lofton said. Plus, many people turn to food as a source of comfort when they feel stressed or unhappy, Burguera said.

Americans’ stress levels are actually trending downward, with adults ranking their mean stress levels at 4.9 on a 10-point scale in 2014, down from 6.2 in 2007, according to the American Psychological Association’s “Stress in America” survey. But this is still higher than what they said they believe to be a healthy amount of stress. And those at lower income levels, with extreme stress about money, were more likely to use food as a source of comfort than those at higher incomes.

4. Sleep deprivation

Lack of sleep is also linked to weight gain. Because of spending later hours using devices like smartphones and tablets that disrupt the sleep cycle, plus increased stress, sleep has become a factor in the fight against obesity. Not getting enough sleep affects hormone levels that increase hunger, Burguera added, and those who are lacking in quality sleep may also be less likely to have the energy to exercise.

In the U.S., 40% of adults sleep less than seven hours a night, according to a Gallup poll in 2013. That isn’t a decrease from the amount of sleep they reported getting over the last 10 years, but it is a full hour less of sleep per night than Americans got in the 1940s.

5. Other illnesses

Illnesses such as depression can cause increased appetite for some people, causing weight gain (although as Ochner noted, depression can actually cause lack of appetite for others). Some people who take medications, including those prescribed for ailments including depression and nerve pain, or even hormones for in-vitro fertilization, may also experience weight gain, Lofton said.

Because the reasons for gaining weight are complex, and problems in nutrition are just beginning to be better understood, a noticeable reduction in obesity could take 10 years or more, Lofton and Ochner said.

Lofton, Ochner and Burguera said that although it’s difficult to point to one solution for this multifaceted problem, financial incentive programs, from insurance companies and employers, and better education could help.

Communities should work to build safe play areas for children, Burguera said, and those in the medical profession should increase their efforts to inform the public about the health risks associated with weight gain.

Lofton also said she would like to see changes in the ways certain foods are marketed, including clearer nutrition labeling that is easier to understand.