The #1 Cause of Weight Gain, Says Dietitian

Compared to 60 or even just 50 years ago, Americans burn fewer calories every day through movement and consume more calories. The result? Over 42% of Americans were obese in 2018, according to the Centers for Disease Control and Prevention (CDC). That's 12% more than it was just 18 years earlier.

"That calorie imbalance is the greatest problem, the number one cause of weight gain," says registered dietitian nutritionist Grace A. Derocha, RD, a national spokesperson with the Academy of Nutrition and Dietetics. "Genetics play a role, but at the end of the day if you eat more calories than you burn off, you will gain weight."

And that has become increasingly easy to do because we eat more calorie-dense processed foods and fewer whole foods than ever before. And we sit a lot. By siting more—teens about 8.2 hours a day and adults 6.4 hours, which is a full hour more than these age groups did just 15 years earlier, according to a JAMA study—we burn fewer calories and experience an increased risk of obesity, multiple other diseases, and even mortality.

If you think about the ancient hunter-gatherers and farmers, they were lean because they were active all day searching for food and working on the farm, says Derocha. Even half a century ago (over ten thousand years after hunter-gatherer cultures), kids and adults were still moving more than we do today. "When I was a kid, food wasn't scarce, but we were outside all day long, running, playing, burning off those calories we ate," she says. "There were very few overweight kids in my neighborhood."

Weight gain happens when you consume more calories than your body needs. As a result, your body will store these extra calories as fat. "You have x amount of fat cells in your body," explains Derocha. "A surplus of calories can increase the number of fat cells and their size. In addition, eating processed foods puts more chemicals into our system that confuses our body. The more toxins, the potential for things to go wrong."

Read on to learn more about how excess calories are the number one reason behind weight gain and what you can do about it. For more on how to eat healthy, don't miss Simple Ways to Start Losing Weight Immediately, According to Science.

The Simple Math Solution

You can see the way out of this common conundrum: Avoid calorie-dense processed foods, consume fewer calories overall, and try to burn off more calories all day through movement, including exercise. In short, create a calorie deficit: ending the day with fewer calories than you consumed results in weight loss.

Easier said than done? But it can be done. And it starts by understanding the simple math of weight gain.

Researchers have calculated that 1 pound of body fat stores about 3,500 calories of energy. So, let's say you cut 500 calories from your intake every day for a week. That's 500 x 7 = 3,500 calories. You would lose 1 pound of fat in seven days.

There's another way to lose that pound that doesn't require you to cut as many calories per day: move more. Theoretically, if you burned off 200 extra calories per day through exercise and sliced just 300 calories from your daily diet, you would still end up with a calorie deficit of 3,500 at the end of the week—a pound of fat gone.

So, you see, to achieve that 3,500-calorie deficit you can either cut 500 calories a day through diet, or burn an extra 500 calories per day through exercise, or do a combination of both.

Simple, right? But there's something else to take into consideration: the calories your body uses daily just to power your life—to breathe, pump blood, digest food, grow muscle, do crossword puzzles, and more. That amount of energy you need to exist is called your Basal Metabolic Rate (BMR) or Resting Metabolic Rate (RMR), your total daily energy expenditure in a resting state. That number is unique to you, determined by your genetics, sex, age, body size, and the amount of muscle you have. Knowing your BMR can make it easier to create the right calorie deficit through calorie restriction, exercise, or a combo of the two. To learn how to calculate your BMR, read our article You Should Burn This Many Calories Per Day, Say Experts.

The Reality Check

While the concept of creating a calorie deficit is the simple math of losing pounds, we all know that keeping the weight we lose off long-term is challenging. That's because as we lose weight, our body's energy needs to change. The pounds that came off so easily when we started become more difficult to shed as we continue our weight-loss journey. The slow-down in weight loss, often described as a plateau, is disappointing. It can take the wind out of your sails and make it more difficult to keep up your focus on the changing math as your body and BMR change.

That's why most dietitians and nutritionists counsel their patients to work on establishing broad healthy eating habits rather than emphasizing the daily number crunch of calories in, calories out.

"I never want my clients to feel like they are depriving themselves," says Derocha. "Food is so much more than calories; it's tied up in family, friends, memories, culture. That's why fad diets don't work. You want real change that doesn't feel so uncomfortable."

Try 'Habit Stacking'

Focus on nourishing your body rather than depriving it. "Ask yourself 'what is something I can add that I'm currently not enjoying?'" says Derocha. She calls it 'habit stacking,' for example: cutting out doughnuts and replacing them with something naturally sweet like watermelon chunks. "Habit stacking feels like you're adding something good for your body and not always taking things away."

Replace the Calorie Bombs

Derocha's two easiest pieces of weight-loss advice are… to (1) drink more water and (2) eat less processed foods.

Making those two lifestyle changes will automatically significantly reduce your daily calorie intake if you drink soda and other sweet beverages and eat a lot of cakes, cookies, salty snacks, and fast food.

"I wish I drank pop so I could stop and lose 10 pounds!" laughs Derocha. Soda, juice, energy drinks, and what she calls "coffee milkshakes" are loaded with sugar and empty calories.

"Focus on enjoying as many whole foods as possible and you'll consume far less processed stuff," she says.