Serotonin and Protein: Fruit Flies Study May Reveal Clues to Appetite and Aging


When humans feel hungry, protein-rich treats like nuts, cheese and meat are what really satisfies the appetite. What is it about protein food choices that does the trick when we’re hungry?

Why do fruit flies also exhibit the same feeding habits? How does it relate to life span and aging? These are the questions researchers at the University of Michigan Medical School are asking. The team suggests that a brain chemical may be the key to the answer.

In Brief: Serotonin, the “Reward” Chemical

When serotonin is released in the brain after one performs a particular action, a sense of reward or pleasure is felt. eLife reports, U-M scientist Scott Pletcher, Ph.D. and his team examined the role the brain-released chemical plays in the eating habits and longevity of fruit flies.

Serotonin appears to affect fruit flies’ tendencies to seek protein when hungry, instead of sugars, when they have been deprived of food for an extended period of time. Somehow the chemical impacts the value that flies place on protein when hungry and their ability to distinguish which foods contain protein in the first place.

Furthermore, the brain-based reward system appears to influence how quickly the flies aged. Pletcher’s team’s study discovered the flies lived a longer life – almost twice as long — when the reward was blocked, versus the flies who ate the same amount of food with the rewarding effect in tact. It is still too early to find definite understandings of how serotonin affects humans’ eating habits or longevity; however, serotonin affects humans in similar ways as the fruit flies, Pletcher says.

The Findings:

According to Pletcher’s study, protein-rich diets have previously been found to shorten lifespans, “These results suggest that serotonin is directly involved in this process, though we have not yet found the mechanism.”

By limiting the amount of protein consumed, yet still eating enough to prevent starvation, the effect was slowed-down aging and extended life spans. However, if flies could still “smell” food in their environment after eating the reduced intake, their lifespans decreased.

The purpose of the study was to scratch the surface of how food affects health and lifespan. Protein is essential for maintaining and building cells, operating differently than sugars and carbohydrates, which provide energy. Further research in fruit flies will help the researchers understand why protein is the most appealing choice and delivers the most satisfying reward when hungry, and furthermore, how to harness the ability to evaluate food to control lifespan and aging.