Fatty and sweet foods are a dieter’s downfall

A study says the combination hijacks the brain’s consumption limits.

It may have taken thousands of generations of hunting, gathering, farming and cooking to get here. But in the end, the genius of humankind has combined fats and carbohydrates to produce such crowning culinary glories as the doughnut, fettuccine Alfredo, nachos and chocolate cake with buttercream frosting.

It goes without saying that these delectables do not exist in nature. It turns out combinations of carbohydrates and fats generally do not exist in the landscape in which man evolved.

Neither, new research finds, does the human capacity to intuit the caloric content of such gustatory delights. Instead, the human brain, when confronted with foods that combine fat and carbohydrates, responds with a surge of motivation that outstrips the response to foods high in fat only or in carbohydrates only.

The study just published in the journal Cell Metabolism doesn’t really tell us something we didn’t at some level know: We eat too much, and too much of the wrong thing, and we’re paying the price in higher rates of heart disease, diabetes and cancer, and in lives shortened by obesity.

But it does shed some light on why, and why we find everything from the dowdy Ritz cracker to the most sublime pastry confection so very irresistible: It’s that diabolical combination of fat and carbs. Calorie for calorie, it found, we’ll take something fatty and easily converted into sugar over something that’s just fatty or something that’s just high in carbs.

The authors of the new study just published in the journal Cell Metabolism went about showing this by collecting 56 lean study participants with an average age of 25. A few hours after feeding these subjects a breakfast designed to leave them somewhat hungry, researchers gave their recruits a small monetary allowance, showed them 39 pictures of different foods that would be familiar, and asked the subjects to place bids on those they’d most like to eat. If they outbid the computer, they’d be allowed to use their allowance to buy and eat that item.

The subjects were also asked to judge how calorific each food item they saw was, and to say how much they liked the pictured food. All of the portions pictured contained the same number of calories. But one-third of the pictures were of items high in carbohydrates, including jelly beans, white bread and spaghetti, one-third were foods high in fat, such as plump wedges of cheese and slices of salami, and onethird were foods that combined fat and carbs, such as buttery crackers, chocolate candies, and pastry.

Finally, the subjects looked at the pictures while having their brains scanned to see which region became most active as they pondered different foods.

The researchers found that no matter how much subjects said they liked items that were fatty or carby, they were willing to pay most for items that combined fat and carbs. And their brain activity while looking at the pictures told the same story: They might score their liking of salami or jelly beans just as high as for cake or crackers. But the items that prompted the reward circuits of their brains to come most alive were the carb and fat combinations.

When asked to rate the items’ calorie content, subjects were a good judge of the fatty items’ value. But they fared more poorly judging the calories in carbohydraterich snacks, and in snacks that combined fat and carbs.