Work groups at the university under Professor Peter Schieberle and at the University of Vienna under Professor Veronika Somoza studied four different edible fats and oils: lard, butterfat, rapeseed oil, and olive oil.
Over a period of three months, the study participants ate 500 g of low-fat yogurt enriched with one of the four fats or oils every day, as a supplement to their normal diet.
"Olive oil had the biggest satiety effect," said Schieberle, Head of the TUM Chair of Food Chemistry and Director of the German Research Center for Food Chemistry. "The olive oil group showed a higher concentration of the satiety hormone serotonin in their blood. Subjectively speaking, these participants also reported that they found the olive oil yogurt very filling." During the study period, no member of this group recorded an increase in their body fat percentage or their weight.
The findings were surprising because rapeseed oil and olive oil contain similar fatty acids. The researchers decided to turn their attention to a completely different type of substance—the aroma compounds in olive oil. In the second part of the study, one group was given yogurt with olive oil aroma extracts and a control group was given plain yogurt.
The researchers found that the olive oil group's calorie intake remained the same, but the control group had been consuming 176 extra calories a day even though both yogurts had the same calories. It was noted in the study that the olive oil aroma group adapted their eating habits, but the control group participants were not able to do the same. In addition, in comparison to the aroma group, the control group had less of the satiety hormone serotonin in their blood.
How long the feeling of satiety lasts after eating depends on a number of factors, but blood sugar level is particularly significant. The faster it falls, that is to say, the faster the somatic cells absorb glucose from the blood, the sooner the person will start to feel hungry again. In the next part of their study, the researchers investigated which of the aroma substances present in the oil are most effective at inhibiting glucose absorption.
The researchers used olive oils from Spain, Greece, Italy, and Australia for their study. The research team managed to identify two substances that reduce the absorption of glucose from the blood in liver cells: hexanal and E2-hexenal. They also discovered that Italian olive oil contained larger amounts of the two aroma compounds.
"Our findings show that aroma is capable of regulating satiety," concluded Schieberle. "We hope that this work will pave the way for the development of more effective reduced-fat food products that are nonetheless satiating."