Even if you eat nutritious food, you might not be eating smart. When we know a food is healthy, we tend to think it doesn’t matter how much we eat, says Paige Smathers, R.D.N., a nutritionist based near Salt Lake City, Utah. Since the wrong serving size can be just as detrimental to your diet as the wrong food, here’s the right way to serve up 10 healthy but tricky snacks. (And might we suggest these New and Improved Low-Calorie Snacks to Tame Cravings? We tested ’em all, and they’re delicious.)

Cereal
If you’re filling a standard bowl with cereal in the morning, you’re probably downing around two cups, says Katherine Isacks, R.D., a nutritionist based near Boulder, Colorado. This mistake is common: “People really do not have a handle on their portion size for cereal,” says Isacks. Check the serving sizes on your favorite boxes—they’re usually 3/4 cup to one cup. If you’re eating more than one bowl, as many people do, that’s an even bigger problem, even if it’s not a sugary version. “The healthiest high-fiber cereal can end up being a very high-calorie and carb-loaded breakfast if you overeat,” says Isacks. She suggests purchasing a small bowl that fits just a cup. Fill it, enjoy it, and be done. (Serve up one of The Healthiest Cereal Choices to Help You Live Longer.)

Orange Juice
The first problem with juice is that it’s inferior to the whole fruit. Oranges have fiber and likely pack more antioxidants than the processed, liquid form, says Isacks. (Learn the whole story in What’s Healthier, Oranges or Orange Juice?) However, if you can’t imagine breakfast without the drink, this is another time to recalibrate your place setting. Most people fill and down a 7-ounce glass or worse, a 12-ounce glass, the latter of which packs 175 calories and 31 grams of sugar! Buy the smallest juice glass you can find and fill it 3/4 of the way, says Isacks. The ideal portion size to keep your carb and calorie intake in the reasonable zone is 4 ounces.

Cheese
Although cheese is packed with calcium and protein and is actually very nutritious, it’s calorie-dense. A half-cup of shredded cheddar, for instance, packs 229 calories. Cheese can be especially problematic for women who’ve cut back on meat and use cheese as a substitute, says Isacks. “They’ll eat 3 ounces of cheese for their main protein, and they’re getting maybe double or triple the calories than if they’d had a lean pork tenderloin or chicken breast,” she says. Her advice: Think of cheese as a flavoring agent and opt for bold varieties like goat or blue cheese to sprinkle small amounts (about an ounce) on eggs and other dishes (like The 10 Best Cheese Recipes to Satisfy Your Cravings.). That way you get just as much flavor for fewer calories. For snacking, buy cheese sticks to take out the guesswork of cutting one ounce off the block.

Yogurt
When you buy yogurt in a large container, it’s easy to scoop too much. Aim for about 6 ounces, or 3/4 cup, at a time, says Smathers. Measure it out, at least the first time. “Take a mental picture of what that looks like, and then every time you eat yogurt, aim for that portion size,” says Smathers. Of course, the type of yogurt matters too. Always reach for plain Greek yogurt—you don’t have to worry about sugar, and you won’t have to be quite as guarded about your portions (eating 9 ounces instead of 6 of the full-fat kind will only cost around 80 calories). But even with good food, it’s important to keep portion size in check so that you can fill out your diet with a variety of nutrients, Smathers says. (Try one of these 10 Savory Greek Yogurt Recipes.)

Popcorn
This one depends on whether you’re eating in front of Netflix or an IMAX. The ideal popcorn is homemade using an air popper, not slathered in butter or sugar. Then you can eat 3 or 4 cups, no big deal, says Smathers. (It’ll only cost you 100 calories or so.) You can also get away with eating a low-calorie mini bag of microwaveable popcorn. The movie theater, however, is a different story. “You have to think about what’s been put on the popcorn, and that changes how much is a reasonable portion size,” she says. Even the smallest bag at Carmike Cinemas, for example, is 530 calories. If you really want it, buy the smallest option and split it with a few friends. Limit your share to about 2 cups, and don’t make this a regular occasion, says Smathers. (Give your popcorn a flavor upgrade with one of these Healthy Popcorn Recipes with Tricked-Out Toppings.)

Avocado
Holy guacamole! Even though the average American eats about half of an avocado at once, the recommended serving size is only 1/5 of the fruit, according to CDC data. But don’t worry too much about cutting a 20-percent slice. “I think a good way to approach an avocado is anywhere from a quarter to half at a time,” says Smathers. The healthy fats in avocados will help you feel full while providing the creamy, satisfying texture your taste buds want. The problem with eating the whole fruit? It’s over 300 calories. (Change it up with 10 Savory Avocado Recipes (That Aren’t Guacamole).)

Pasta and Rice
Many people fill half or more of their plate with these starchy sides. That’s a problem because pasta or rice should only take up a quarter of that real estate, says Smathers. Since we know that these foods aren’t the smartest picks, it’s easy to tell yourself to go big or go home. That’s a problem because when you eat a plateful of spaghetti, you’re downing way more calories and carbs than you need. Plus, you’re not getting enough protein and fruits and vegetables. “If you put pasta on first, there’s not likely to be much room left for anything more than a couple sprigs of broccoli,” says Seattle-based nutritionist Marlene Maltby, R.D.N. (Skip the guilt: 15 Low-Calorie Pasta Recipes for a Healthy Italian Dinner.)

Nuts
The healthy fats in nuts have been linked to a variety of health benefits. However, their good reputation can lead to problems: Because people think of nuts as a “good” food, they think they can eat however much they want, says Smathers. A quarter cup, or a small handful, is a smart serving. To help you stick to that, buy raw unsalted nuts, suggests Smathers. Our bodies are programmed to crave salt, so it’s hard to put salty nuts down. It’s easier to stay in control with unsalted nuts because you’ll actually get sick of the flavor after a while. Rather than leaving them in the canister or bulk container, portion the nuts into small bags so you have the proper serving ready at all times. Pair them with fresh fruits or vegetables to help you fill up without loading up on calories, suggests Maltby.

Nut Butters
Heaping spoonfuls aren’t your friend. Like nuts, nut butters can be nutritious, but they pack plenty of calories and go down even easier than nuts. Measure out 2 tablespoons of nut butter so that you can see what it really looks like. Aim for that much every time you eat it, says Smathers. (Here’s 40 “Betcha Never Tried This!” Ways to Eat Nut Butter.)

Trail Mix
It’s incredibly easy to eat too much trail mix. So much so, in fact, that Smathers usually recommends trail mix to clients looking to gain weight. If that’s not you, stick to a 1/4 to 1/2 cup, placed in zippered plastic bags so you can’t go overboard. The typical components of trail mix tend to be high in calories (nuts, for example) or high in carbs (like dried fruit and candy pieces). For a high-protein mix, Smathers stirs together coconut flakes, raw nuts, and dried cranberries (it’s The Ultimate Healthy Trail Mix).

Bottled Smoothies
Check the label: Often these products pack multiple serving sizes. If you guzzle the whole thing, you’ll down plenty of carbs and calories, but probably not much filling fat and protein. “The problem with that is that carbohydrate doesn’t really give you lasting energy,” Smathers. “It gives you immediate quick energy but you do kind of crash on it quickly, and you get hungry soon and it can lead to eating more.” You’re better off making a 12-ounce smoothie at home with fruit and full-fat plain Greek yogurt, says Smathers. (Change up your usual recipe with one of these 14 Unexpected Smoothie and Green Juice Ingredients.) However, the convenience of a bottled smoothie does give it a special place in your diet—on the go, at the airport, etc. Drink half of it and pair it with something rich in protein and fat.