The reason why donuts are just so gosh darn irresistible? Fats and carbohydrates, says a new study. Certainly, there's nothing quite like fats and carbs combined together. Each is nice on its own — but when they unite, the brain just can't handle it.

That's why french fries, muffins, and ice cream are so addictive, the study says. A team of researchers from Yale University wanted to look at the neurological explanation behind the deadly combination of fats and carbs; they wanted to know what makes them so tempting even for people who claim not to like them.

The study was published in the Cell Metabolism journal.

Why Carbs And Fats Are So Irresistible

The researchers asked people to look at pictures of three kinds of foods: those rich in carbs, those rich in fats, and those that have plenty of both. During this process, the researchers took fMRI images of participants' brains in an attempt to determine their neurological responses.

They were also asked to guess the density or caloric content of each just basing on the images alone, and they also stated how much they were willing to pay for them.

The team found that the participants were generally good at guessing the energy density of fatty foods. However, they weren't very good at estimating how many calories there were in foods that were high in both fats and carbs, which could explain why it's difficult to know when to stop eating them.

Unsurprisingly, people were willing to pay extra for carb and fat-rich foods as opposed to foods with just carbs or fats alone. Interestingly, the amount they said they'd pay wasn't linked to how much the person said they liked the foods, which suggests that fats and carbs together have an entirely different appeal even to people claiming they don't like it.

fMRI scans also revealed that the participants' brains lit up more when shown foods with both fats and carbs, no matter the portion size, caloric content, and sugar level. It suggests these foods activate reward centers in the brain, and that they might be as appealing the way drugs are addicting.

"Our study shows that when both nutrients are combined, the brain seems to overestimate the energetic value of the food," said lead author Dana Small, of the Modern Diet and Physiology Research Center at Yale.

More Research Needed

In addition, the study also provides insight into understanding how the food environment contributes to the obesity and diabetes pandemic.

"In the modern food environment that is rife with processed foods high in fat and carbohydrate like donuts, French fries, chocolate bars, and potato chips," said Small, "this reward potentiation may backfire to promote overeating and obesity."

That being said, it's not without its blind spots. For starters, it failed to evaluate what participants normally eat in their daily lives. What's the difference between someone who eats fats-and-carbs foods regularly and a person who never does but is offered some? Furthermore, the study only looked at a small pool of participants in Western Europe. A larger-scale study would provide more compelling results given that eating habits can differ by culture.

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