The National Institutes of Health is conducting a study to help determine why so many people can’t stop eating ultra-processed foods. The study includes 36 participants living in a controlled setting for a month. They can eat as much as they like up to 6,000 calories per day, with a different type of diet each week.

One diet includes minimally processed foods such as oatmeal, strawberries and walnuts. Another diet involves ultra-processed, energy-dense (high-calorie) meals with most calories coming from hard-to-resist foods such as honey-roasted peanuts. A third diet is also ultra-processed and energy dense, but with fewer calories from the hyper-palatable items. The fourth diet consists of packaged foods that are neither energy-dense nor hard to resist, such as scrambled eggs from a liquid egg product, flavored yogurt and oatmeal with fiber powder and heavy cream.

Preliminary data from 18 of the participants found that while each diet made them feel full and satisfied, their consumption of calories differed, depending upon how hard-to-resist and energy-dense the food choices were. When subjects were given an energy-dense diet with very palatable foods like honey-roasted peanuts, they consumed about 1,000 more calories than with the other diets. When they were offered an ultra-processed diet that was neither energy-dense nor hyper-palatable, the calorie count increased by only 170.

The findings suggest that eating packaged foods does not automatically result in overeating or weight gain. The key may be avoiding hyper-palatable foods and offsetting energy-dense foods with unprocessed foods like salads.