A lot of food research hinges on the honesty of participants about what they’ve eaten, as well as the accuracy of their memories.

It’s possible for researchers to end up with false conclusions—for example, about how much junk food our bodies can manage—if participants don’t tell the whole truth about how many chips actually went down the hatch last Monday night.

“Many people forget to—or don’t want to—truthfully report back what they’ve eaten. As such, we found a method that uses urine tests to examine the substances present in our body after various foods are consumed. By doing so, we hope to contribute to eventually being able to conduct improved, more objective research,” explains Cristian De Gobba, an assistant professor in the University of Copenhagen’s food science department.

De Gobba and colleagues analyzed urine samples from 10 people living in Denmark to identify which substances were present after eating potatoes cooked in various ways. Their findings appear in the Journal of Agricultural and Food Chemistry.

Five men and five women, ages 24-46, received a special dietary plan to follow for one week. Some had to eat boiled potatoes, others potato chips, and others french fries. Thereafter, the researchers examined the participants’ urine samples to look for differences in the substances found.

“We used mass spectrometry, an analytical technique that separates chemical substances by their mass. To give an example, the mass of sugar is different than the mass of protein,” explains De Gobba.

“In doing so, we measured the exact mass of individual molecules allowing thousands of different compounds to be analyzed simultaneously and made it possible for us to group substances. Our study showed that certain substances are more present in french fries and chips than in boiled potatoes.”

For example, some pyrroles—associated with poor nutritional value and the potential to damage our ability to regulate sugar—are more abundant in deep-fried potatoes than in boiled ones.

While there are indications that the substances in the deep-fried foods are unhealthy, researchers still lack much of the knowledge needed to map the health effects of those substances found in the participants’ urine.

“We have yet to discover if the substances are specific to potato products, or if they are found more broadly, among all types of heated foods. Nor are we able to claim with certainty whether the substances present increased health risks,” says Lars Ove Dragsted, a professor and section head in the department of nutrition, exercise, and sports.

While more studies are required to fully determine the health characteristics of specific food products, the new method is a small step towards improved and more valid food and nutrition research.