Take off that Fitbit. Exercise alone won’t make you lose weight.

The obesity problem has little to do with our sedentary lifestyles.

The fitness industry has never been stronger. Health clubs in the United States brought in $22.4 billion in 2013, doubling their revenue in just 15 years. Sales of fitness trackers (the wearable devices that measure everything from your daily steps to your blood oxygen level) are expected to triple within the next five years. And health and fitness apps were the fastest-growing downloads from Google’s app store last year. Still, obesity has continued to surge around the world. Nearly one in three people alive today is overweight or obese — two out of three adults in the United States — and no country has lowered its obesity rate since 1980.

That’s not a fluke. Our waistlines aren’t expanding because people aren’t exercising intelligently or vigorously enough. You don’t need a new personal trainer, another Insanity workout video or a more aggressive CrossFit regimen. What you need is the truth, and here it is:

Exercise — no matter how many gym memberships you buy or how often you wear your Fitbit — won’t make you lose weight.

The idea that our obesity epidemic is caused by sedentary lifestyles has spread widely over the past few decades, spurring a multibillion-dollar industry that pitches gadgets and gimmicks promising to walk, run and kickbox you to a slim figure. But those pitches are based on a myth. Physical activity has a multitude of health benefits — it reduces the risk of heart disease, Type 2 diabetes, high blood pressure and possibly even cancer — but weight loss is not one of them.

A growing body of scientific evidence shows that exercise alone has almost no effect on weight loss, as two sports scientists and I described in a recent editorial in the British Journal of Sports Medicine. For one, researchers who reviewed surveys of millions of American adults found that physical activity increased between 2001 and 2009, particularly in counties in Kentucky, Georgia and Florida. But the rise in exercise was matched by an increase in obesity in almost every county studied. There were even more striking results in a 2011 study published in the New England Journal of Medicine, which found that people who simply dieted experienced greater weight loss than those who combined diet and exercise.

How can this be explained? When people exercise, they stimulate their appetites, spurring them to eat more than they would have without working out. People also assume that expending more energy necessitates higher calorie intake, but they often overestimate how much. In reality, if you exercise for the purpose of burning calories, you get a very low return on investment: You would have to walk for more than 45 minutes to burn off the 300 calories from eating just three cookies.

On top of that, the idea that physical activity speeds up our metabolism so our bodies consume calories more quickly is exaggerated. In a study published in 2012, a group of anthropologists measured the daily physical activity, metabolic rates and energy expenditure of people in a hunter-gatherer tribe in Tanzania, and compared the results to the average Westerner. Though the Tanzanian subjects were more physically active than Westerners, their metabolic rates were similar. In other words, the researchers concluded, “active, ‘traditional’ lifestyles may not protect against obesity if diets change to promote increased caloric consumption.”

Trial evidence consistently reveals that basal metabolic rates tend to drop as people lose weight, despite daily exercise. A comprehensive 2013 literature review by Amy Luke, a public health scholar at Loyola University of Chicago, concludes that “numerous trials have indicated that exercise plus calorie restriction achieves virtually the same result in weight loss as calorie restriction alone.”

It’s calorie intake that is really fueling the obesity epidemic. But it’s not just the number of calories we’re eating as how we’re getting them. The sugar calories are particularly bad. Stanford University researcher Sanjay Basu recently led an analysis of 175 countries that evaluated the amount of sugar in each nation’s food supply. As sugar availability increased by 150 calories per person per day (the equivalent of a can of cola), there was a 1.1 percent rise in the prevalence of Type 2 diabetes in the population — an increase that was 11 times larger than if people consumed 150 more calories from nonsugar sources — independent of average body mass index and physical activity levels. The experience of Timothy Noakes, a leading sports and exercise medicine scientist, exemplifies those results. Despite being an almost daily runner and completing more than 70 marathons in his lifetime, Noakes developed Type 2 diabetes in his late 50s, which he attributes to his excessive consumption of sugar and other refined carbohydrates.

Yet the public continues to be smothered with messages about the importance of maintaining a healthy weight through calorie-counting and physical activity. The food and beverage industry is most guilty of perpetuating the false belief that the obesity epidemic is simply due to lack of exercise, spending billions to market nutritionally poor products as “sports drinks” while simultaneously promoting the benefits of physical activity.

Sadly, many doctors’ understanding of nutrition is influenced by bogus industry advertising. In July 2012, I stopped drinking the popular sports drink Lucozade after Oxford University researchers found a “striking lack of evidence” to support claims that such products enhance performance and recovery. Instead of wasting close to $10,000 over the previous 15 years drinking a product loaded with seven teaspoons of sugar, I would have been better off drinking tap water at the gym. The World Health Organization now recommends no more than six teaspoons of sugar a day for the average adult.

Misconceptions about diet and exercise are paralyzing efforts to curb the worsening obesity crisis. The food industry has been central in pushing these misconceptions, using tactics similar to those employed by big tobacco, to elide its culpability in spreading disease. In a 2009 paper published in the Milbank Quarterly, a public health journal, researchers found that the food industry has formed close ties with influential politicians and scientists who give it powerful avenues to quash policies and research that highlight the harms of sugar. This strategy also allows it to push the message that personal responsibility and a lack of physical activity are really at the root of public’s obesity problem. Reuters found that the food and beverage industry spent more than $175 million on lobbying during President Obama’s first three years in office, more than doubling its spending under the last three years of George W. Bush’s administration, targeting proposals like a federal tax on sodas and stricter nutritional guidelines.

Even the Obama administration has waffled on the issue. First lady Michelle Obama’s initial efforts to raise awareness of the importance of healthy eating for children were commendable. In 2009, she even planted her first garden on the White House lawn, with broccoli, spinach and other vegetables. But a year later, that emphasis on nutrition was undermined by her new focus on physical activity with the Let’s Move campaign, based on the unfounded notion that more exercise is key to solving obesity.

None of this means you should turn in your gym membership card. Working out will make you healthier and less susceptible to disease. No matter what your size, even 20 to 30 minutes of physical activity that breaks you into a sweat five times per week will substantially improve your health and well-being. Do what you enjoy, whether it’s dancing, cycling, sex or all three. If it’s longevity you’re after, note that elite athletes in high-intensity sports don’t live any longer than top golfers.

But if weight loss is your goal, your diet is what really needs to change. An analysis by professor Simon Capewell at the University of Liverpool revealed that poor diet (for example, eating too much junk food without enough nuts, whole grains, fruit and vegetables) now contributes to more disease and death than smoking, alcohol and physical inactivity combined. And up to 40 percent of those with a normal body mass index harbor metabolic abnormalities that are associated with obesity, including high blood pressure, nonalcoholic fatty liver disease and heart disease.

Corporate greed and a systematic political failure to protect citizens from the manipulations of the food industry have brought American health care to its knees. More than 75 percent of health-care costs now go toward treating chronic metabolic diseases and their associated disabilities. These problems are a result of food industry spin and false information linking physical inactivity and obesity. Curbing the global obesity problem will require changing what we eat, not selling more pedometers and exercise videos. The bottom line: You can’t outrun a bad diet.

Using Fitbit to help kids lose weight


Researchers in St. Petersburg, Fla., are conducting a study to determine whether using Fitbit activity trackers and other technology can help teens lose weight. (Whitney Shefte/The Washington Post)