When it comes to the numbers on your scale—whether you want them to go up or down—it’s all about calories in versus calories out. But that’s not always as simple as it sounds. Here are five head-scratching, WTF reasons you’re taking in way more than you’re burning.

You Buy Groceries with a Credit Card

If you’re paying with plastic, you’re apt to put 42 percent more junk food in your trolley, according to research from Cornell University. For most people, unhealthy foods are an impulse purchase, and the paper-plastic connection can contribute to this.

When you’re paying with credit as opposed to handing over a crisp R100 note, it’s just easier to follow those impulses. “When you pay cash for something you ‘feel’ it more,” says Christopher Ochner, Ph.D., a nutrition and obesity expert at Mount Sinai Hospital. Writing a shopping list and actually sticking to it—along with hitting the aisles with a full stomach—can also help keep your impulse purchases at a minimum and you away from munching on junk calories to excess later.

You Live at Sea Level

The lower your city, the higher your BMI may get. In a recent U.S. military study, researchers examined the health and locations of nearly 100,000 active members of the U.S. Army and Air Force and found that over a period of seven years, overweight service members were 41 percent more likely to become obese if they were stationed at military facilities located at a low altitude.

Why? Previous research suggests that the uptick in red blood cells people experience at high altitudes—a response to the lower concentrations of oxygen—may result in the body producing more appetite-regulating hormones. It’s also true that when there’s less O2 in your air, basically everything you do costs more energy and burns more calories, Ochner says.

You Travel for Work

If you spend a lot of your time in airports, chances are you’re racking up more than miles, according to one Columbia University study that reviewed the medical records and travel habits of more than 13,000 workers. Researchers found that those who traveled the most for work were more likely to have higher BMIs and a greater risk of obesity.

A lot of this may come down to eating out versus cooking in, says Ochner, who warns against falling for the notion that “fine dining” is healthier than your average burger joint.

You’re Addicted To Comfort

Comfortable isn’t always a good thing. It turns out, when your home’s temperature is always “just right,” your body doesn’t have to work to cool itself down or warm itself up, meaning your body burns fewer calories day in and day out, according to research published in the International Journal of Obesity.

If you’re going to put your thermostat to use, though, set it cool—and at night. A recent study published in the journal Diabetes found that when men spent a month’s worth of nights sleeping in a cool room, they increased their levels of brown fat—the “good fat” that burns calories to generate heat—which could theoretically boost metabolism.

You’re a Multitasker

The more you do at once, the less control you have in the face of fried foods. Research from Emory University shows that juggling a bunch of tasks at once (think: your everyday reality) can wear out your brain’s executive function, which is in charge of keeping up your self-control.

Instead of toggling back and forth between to-do-list tasks, try tackling just one project at a time. That especially holds true when junk food is anywhere near your desk. Myriad studies show that when you’re distracted, you just don’t realize how much food you’re shovelling in.