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Twenty years ago, a small popcorn at a movie theater had just 270 calories; today, it has 650 calories. And a tub of popcorn these days can top 1,600 calories. Of course, you don’t have to eat the whole bucket. But there’s a good chance you’ll scarf down at least a large portion of it.

Faced with an abundance of food, we have a hard time saying no, according to a 2015 review of 72 studies published by the Cochrane Library. “Research consistently shows that when we’re presented with a big portion, we eat more — even when we are not hungry,” says Lisa Young, author of “The Portion Teller Plan” and an adjunct professor of nutrition at New York University.

So can shrinking our waistlines be as simple as bringing serving sizes down a notch? That can help, Young and other experts say. But downsizing portions is only one piece of the puzzle. For weight control and good health, there are foods you’ll actually want to eat more of. And unless you take steps to ensure that you feel full on smaller portions, your serving sizes will probably creep up again.

Follow the techniques below to help you train your brain to recognize and stick with healthy helpings of food.

Smart-size your meals.

Using portion control as your primary healthy-eating strategy allows you to eat almost any food while keeping calories in check. And the calorie savings are significant: Normalizing portions could reduce calorie intake by almost one-third — about 527 calories per day, according to one study. If all else remains equal, you could lose a pound per week.

Scoop and pour. Pull out some measuring spoons and cups to dole out precise portions of your favorite foods for a few weeks. You might be surprised to see that a serving of the cereal you eat most days is three-quarters of a cup, while filling up the bowl to what looks like a reasonable portion puts you closer to two or three cups. (For a guide to serving sizes, go to choosemyplate.gov.)

Share with a friend. When dining out, start with your own healthy appetizer, such as salad or soup, and split the entree. It’s also wise to go halfsies on extras, like a side of french fries or dessert. And slow down so that you can enjoy each bite.

Watch your portions of healthy foods, too. Plenty of nutritious foods, such as almonds and dates, are high in calories. And when people think that a food is good for them, they underestimate calories, according to a study from Cornell University.

Stay satisfied.

Resized portions will seem small only if they’re not satisfying. By favoring satiating foods, you can feel full from smaller servings.

Focus on fiber. Simply choosing foods that are rich in fiber can help fill you up. In one study, increasing fiber intake to at least 30 grams per day for 12 months helped 240 adults who were at risk for Type 2 diabetes lose almost as much weight as people who followed a more complicated diet that specified exactly how many servings of carbs, vegetables and protein to consume. Fiber-rich choices include beans, fruits, vegetables and whole grains.

Curb your appetite. Take the edge off your hunger with a healthy appetizer; that will help you limit yourself to that one-cup serving of cooked pasta. In a study in the journal Appetite, a salad before or during a meal helped people eat 11 percent fewer calories overall.

Take smaller bites. That can help you keep portions in check. For example, research from the Netherlands found that people who took tinier sips of tomato soup ate about 30 percent less than those who gulped it.

Think big — sometimes.

Supersize the salad. It’s difficult to find fault with a heaping bowl of raw vegetables. So in addition to the standard lettuce, tomato and cucumbers, add asparagus, beets, green beans or whatever vegetables you like. Watch out for the extras, though: Cheese, croutons, wonton noodles and, of course, dressing can catapult a salad’s calorie count into double cheeseburger range.

Eat veggies family-style. Measure out carbs (such as potatoes) and protein (steak, for example) to control portions of higher-calorie foods. But put vegetable side dishes on the table so that people can help themselves to abundant servings of those filling, low-calorie foods.

Increase portions with produce. Not sure a half-cup serving of cooked rice will fill you up? Round it out with vegetables. For example, add a cup of chopped fresh spinach per serving of rice for a bulked-up but not weighed-down side dish. (Mix the spinach into the hot rice as it finishes cooking, stir and cover the pot for a minute. After the heat wilts the greens, stir again before serving.)

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.

Copyright 2016. Consumers Union of United States Inc.