If we eat them separately, the brain shows less interest in the food.
The results showed that the participants were willing to pay more for foods that combined fat and carbohydrates.
"Our participants were very accurate at estimating calories from fat and very poor at estimating calories from carbohydrate and our study shows that when both nutrients are combined, the brain seems to overestimate the energetic value of the food". High-fat and high-carb foods also trumped foods that were sweeter or a larger portion size.
The study found humans had not evolved enough from the days of hunting and gathering to cope with making good decisions about relatively new processed foods high in carbs and fats, such as hot chips and doughnuts.
Let's say that a mouse sees some food, but it doesn't provide energy.
The results of the study showed that the type of hazardous food "includes" in the reward center of the brain has much more neurons than any other option.
It could help explain brain-body mechanisms underlying the genetic predisposition for obesity, eating in the absence of hunger and difficulty losing or keeping off excess pounds. This is because when you analyze the modern highly processed food, you will be aware that your diet contains more than sufficient amount of fats and carbohydrates.
Our hunter-gatherer ancestors ate mostly woody plants and animal meat, the researchers said.
"The simultaneous activation of fat and carbohydrate signalling pathways launches an effect that human physiology has not evolved to handle", they wrote.
Dr Small said: 'In nature, foods high in fat and carbohydrate are very rare and tend to have fiber, which slows metabolism.
Consistent with this suggestion, mice given access to fat or sugar alone regulate their total daily caloric intake and body weight.
"One mechanism by which the modern food environment may promote overeating is by combining fat and carbohydrate to potentiate reward and therefore facilitate the transition to habitual responding as is observed in drugs of abuse".