Before you dig into your next sandwich, you might want to pay more attention to what’s underneath that bread: People who eat sandwiches may take in more kilojoules overall, recent research from the University of Illinois found.

In the study, people reported consuming 418 more kilojoules on days where they ate sandwiches than on days when they ate other kinds of food.

And while an extra 400-odd kilojoules a day doesn’t sound like much, that can translate to gaining about 450 grams over the course of a month, says study coauthor Ruopeng An, Ph.D.

So what is it about the sandwich that sparks you to take in more kilojoules?

One reason may be that we tend to overlook how a few quick condiments can add up, says Men’s Health nutrition advisor Alan Aragon M.S.

Slap on a couple slices of American cheese and 2 tablespoons of mayo, for instance, and you’ve already added over 1255 kilojoules to your meal.

What’s more, when you eat a sandwich, you probably feel tempted to add a side to it: And what goes better with it than chips or fries?

That’s another way you can quickly add kilojoules to your meal, says Aragon.

 But it’s important to recognize that there’s nothing inherently bad about sandwiches—and the study doesn’t prove that eating them directly causes you to pack on kilograms, says Aragon.

There may be other factors at play, too, he says.

For instance, since sandwiches are so easy and convenient, you might just be more tempted to grab one on a super busy day—when you’re also more likely to make other not-so-healthy choices, too, he says.

So you don’t need to trade in your sandwich just yet. You can easily build one—or order one—that packs some serious nutritional value, says Aragon.

Look for 100 percent whole-grain options that pack in fibre and skip lots of additives.

Then, pick lean protein sources like chicken breasts or turkey cutlets, says Aragon. Don’t skimp here: Stuffing in about 85g of protein will help keep you full.

Top the meat off with some vegetables—like lettuce, carrots, or cucumbers—to add a satisfying crunch to each bite.

Avoid fatty, high-calorie spreads like mayo or ranch dressing. It’s easy to spread on way too much, which can turn a previously health sandwich into a gut bomb.

But if you can’t stomach eating your sandwich dry, consider adding low-cal options like balsamic vinegar, mustard, or hot sauce, says Aragon.