If you want to lose weight, will you get better results by eating the same foods but cutting your portion sizes, or eating healthier foods but keeping the size of your meals the same?

Both are smart strategies, but a new Penn State University study indicates making healthier foods choices — that is, foods higher in nutrients and lower in calories — will deliver better results.

“Choosing healthy, lower-calorie-dense foods [is] more effective and more sustainable than just trying to resist large portions of higher calorie options,” said graduate student Faris Zuraikat in a statement. “If you choose high-calorie-dense foods but restrict the amount that you’re eating, portions will be too small, and you’re likely to get hungry,” he said.

Portion sizes have steadily risen over the last few decades (not coincidentally, so have numbers of overweight and obese Americans), so cutting portions seems like an obvious path to weight loss. The problem is that gauging “healthy” portion sizes is a lot tougher than it sounds.

The Penn State study, published in the journal Appetite, demonstrated that by recruiting 102 participants: about a third of these women were normal weight, a third were overweight, and another third were overweight but had participated in a year-long weight-loss course emphasising portion control strategies.

Once a week for four weeks, all the participants visited a laboratory and were provided the same foods — a mix of healthy options (salads, for example) and less healthy options (garlic bread).The research team closely monitored exactly how many calories the women ate from these meals, while playing a cunning trick on them: the sizes of the meals were increased at random, sometimes to almost double the “baseline” size. When portion sizes increased, all the women ate more — even the ones trained on portion control.

However, the women who’d received the training ate fewer calories overall than those who hadn’t, because they made better food choices: eating more of the lower-calorie, higher-nutrient foods and less of the higher-calorie, lower-nutrient foods. The research team suggested the study indicates that focusing on portion sizes isn’t a strategy that works out so well in the real world — but teaching people how to eat healthier is.

“The study supports the idea that eating less of the higher-calorie-dense foods and more of the nutritious, lower-calorie-dense foods can help to manage hunger while consuming fewer calories,” said Penn State nutrition sciences professor Barbara Rolls, a co-author of the paper. “You still have a full plate, but you’re changing the proportions of the different types of foods.”