Why hot chips are so delicious

• Comment: Fast-food restaurants must get with the program to end obesity

Scientists may have discovered why humans love scoffing hot chips - our brains appear to be very fond of fat and carbohydrates combined into one easy-to-eat snack.

A study of 206 adults by The Max Planck Institute for Metabolism Research in Germany, found the brain's reward centre values food items high in fat and carbohydrates (such as chips, doughnuts and most processed junk food) more than foods containing only fat or only carbs.

Study participants underwent brain scans while being shown photographs of familiar food containing a combination of fat and carbs, or only mostly carbs or mostly sugar. The fatty-carb combo foods lit up neural circuits in the brain's reward centre more than other types of food.

Test subjects also reported they were willing to spend more money on food containing a combination of fat and carbs.

"Our participants were very accurate at estimating calories from fat and very poor at estimating calories from carbohydrate," says Dana Small, senior author of the study and director of Yale University's Modern Diet and Physiology Research Center. "Our study shows that when both nutrients are combined, the brain seems to overestimate the energetic value of the food."

It is possible that because foods high in both fat and carbohydrates are rare in nature, our brains are yet to develop a response to regulate their intake. Our ancestors evolved eating meat and woody plants for thousands of years, however hot chips have only been around since the 18th century.

The brain's positive reaction to food items high in both carbs and fat may also help explain how the obesity epidemic took hold.

"Two thirds of Australians are now overweight or obese," says Alexandra Jones, research associate at The George Institute for Global Health's food policy division. "We like to think we're in control of what we eat, but that statistic suggests most of us are failing.

"These findings confirm what many marketers already know - there's money to be made in exploiting our brains' preference for certain unhealthy combinations."

The findings are consistent with previous research that showed rodents given access to carbohydrates or fat alone will regulate their total daily caloric intake, but unrestricted access to fat and carbohydrates led the test subjects to quickly gain weight.

"Fast-food restaurant options such as the easily 'upsized' hot-chip side make it very tricky to choose healthy options in the current food environment," says Jones. "Small changes like swapping hot chips to salad as the default option in a meal combo would make it so much easier for us to resist the stuff driving obesity."