为何薯条薯片会让你欲罢不能?

Ever wonder why foods that are bad for you - such as fat-laced potato chips and French fries - taste so good? It turns out they follow the same pleasure-inducing biochemical pathways through the body as marijuana does, encouraging people to keep eating even when they know they should stop.

There used to be an old television commercial in the United States that boasted a certain brand of potato chip tasted so good, you could never eat just one.  It turns out there is a biological reason for that.

Fat is an important component of healthy human cell membranes and high-fat foods, which are rare in the wild, and were prized by early humans as a rich source of energy. As a result, says Daniele Piomelli at the University of California, Irvine, humans developed a biological preference for fatty foods.

“The mechanisms that have evolved to make animals eat as much as possible now are turning against us because now fat is everywhere," says Piomelli. "We have fat in our refrigerators, in our cabinets in the kitchen and it is very easy for us to eat too much of it because of this long evolution that has taught us that it is rare and hard to find.”

Piomelli's team has discovered a biological pathway that encouraged ancient humans to eat large quantities of the scarce nutrient - whenever they found it - to ensure their survival. Today, eating fat still provokes feelings of pleasure and satisfaction, similar to the high people get when smoking marijuana.

According to Piomelli, when fatty foods are swallowed and hit the upper digestive tract, they trigger the production of endocannabinoids. That's the same class of feel-good brain chemicals that marijuana, or cannabis, stimulates in the brain.

Endocannabinoids in the gut send a surge of cell-signaling to the brain, which shoots back a message telling the body to keep eating.

Piomelli's team discovered the fat pathway in research with rats. The rats didn’t like sugar water or water laced with protein as much as they liked oily water. The animals continued to consume the oil water until they were full, which is the body’s natural signal to stop eating.

But since fats contain more calories than carbohydrates or proteins combined, waiting for satiety, or fullness, is not necessarily the best strategy to limit consumption of fatty foods.

Piomelli says researchers are interested in developing drugs that target endocannabinoids in the digestive tract to help people with their fatty food cravings.

“When some people eat fat, they eat it in large amounts - for example a pint of ice cream or a whole bag of potato chips.  And hopefully by using these type of medications, we can decrease overweight and obesity.”