When Not to Eat: Concerning Fruit Flies, Pheromones and Food


The following article appears in Under the Scope (Volume 3), an SQ journal that features the work done by undergraduate researchers in an accessible and artistic manner. This is a preview for the release of this year’s edition, which will be unveiled at the UC San Diego Student Research Showcase. | More info and RSVP.

Students find how scent attracts us to food and how eating at certain times may change the way our bodies process the food, bringing insight to our eating patterns.

by Brianna Egan, Demiana Sidrak, An Qi (Angela) Yao, Alice Zalan | Staff Writers | UTS Vol. 3 (2012-2013)

The moon glares through your dorm window and your desk spills over with scrawled-out Organic Chemistry notes and plastic ball-and-stick models of alkanes. The menacing growl from your stomach catches you off guard: time for yet another late-night Burger King run. Or is it?

Eating healthy and at regular intervals often falls as last priority in a schedule full of midterms, meetings and meltdowns. However, what if it’s not within your conscious control to decide what to eat?

Generally, people assume you are what you eat. Instead, it turns out that you eat what you are: You are, at a starkly scientific level, a jumble of of organs with a brain that directs them, thus making possible actions such as sleeping and eating. The interplay between neurons and food breakdown may be responsible for what you eat—controlling things such as your desire or distaste for certain dishes and even determining how the body will process foods depending on the time of day. Undergraduate researchers at UC San Diego are beginning to define these biological forces.

Illustration by Aimee Ermel

Illustration by Aimee Ermel

Our attraction for certain smells can be traced to the olfactory system. Beginning at the nose, this system allows us to detect the scents in our environment as our brain processes the thousands of odors we smell every day. Olfactory receptors in the brain detect specific odorants in the environment. As we further explore this system, we can pinpoint the exact neural mechanisms that are involved.

Sniffing Out the Science of Attraction

In Dr. Jin Wang’s neurobiology laboratory, Tricia Ngo conducted research on pheromones, the chemicals secreted by organisms that influence the behavior of members of the same species. The pheromone in this study, cVA (11-cis vaccenyl acetate), is responsible for attracting fruit flies to food sources.

“We came into the research already knowing that cVA was a pheromone for the fruit flies, but we determined which parts of the brain were actually necessary for attraction to it by blocking certain areas,” Ngo said.

Fruit flies (Drosophila melanogaster) were placed onto three separate test plates with either a food source of vinegar, cVA, or both. The flies’ responses showed the greatest attraction to the mixture of cVA and vinegar.

“We’re still trying to find out why the mixture leads to this greater attraction,” Ngo said, “[Now] we are going to look at imaging data as a result of our behavioral data. Using photon microscopy, we will be able to have images of brain activation in response to the cVA.”

Ngo determined that only certain parts of the Drosophila olfactory system are necessary for detecting cVA. Some neurons in the DrosopShila brain inhibit the ability to detect the cVA while other structures in the brain inhibit the attraction to cVA. This means that although the fruit fly can detect the pheromone, it will not display the same attraction response.

To understand the effect, imagine the scent of your favorite freshly-baked cookies wafting your way but feeling no desire to run to the kitchen and eat because a part of your brain is turned off. Just as the fly’s desire to eat is largely based on its ability to pick up on scents, hungry students rely on cravings—or a lack thereof—to fill their stomachs.

In another sector of Dr. Wang’s lab, Lea May Currier explored how the Drosophila flies develop meal preferences early in development.

“What we wanted to do was to basically figure out what the causal experiences are for flies to have preference for a particular smell—and usually a smell related to food,” Currier said.

After hatching, fly pupae were contained in conditioning vials for three days, which Currier determined to be a critical period for flies to develop exposure and preference towards a scent. A group of flies was exposed to apple cider vinegar in the vials and thus conditioned to the scent, while a control group had no exposure to vinegar.

After a period of starvation, female adult flies, whose olfactory senses are stronger than those of males, were introduced into a test plate containing a droplet of apple cider in the center. Blinded by a red light, the flies relied solely on their olfactory sense. If the fly remained at the center for ten seconds, it had made a definite “response” in recognizing the scent. Under what conditions did the flies not respond to the smell? Both the flies left unconditioned and the conditioned flies that lacked certain olfactory receptors altogether passed over the droplet.

Currier performed genetic crosses to create these “knockout” lines of flies lacking specific olfactory neurons and found each of these neurons to be directly needed for a fly’s retrieval of the vinegar, establishing an innate neural-based preference. Currier, who is now taking a gap year before attending medical school, is currently furthering her research.

The Wang lab has introduced a novel calcium imaging method to observe how, at a cellular level, olfactory neurons can be excited by certain scents. They are exploring if flies consume foods due to higher nutritional content. Ultimately, she explains, deciphering food preference in flies can be understood on a larger scale.

“With all these environmental cues, we want to know what makes a fly have an aversion to something toxic and an attraction to something delicious,” Currier said. “We want to figure out how something with such a tiny brain is able to navigate effectively—it all leads back to food preferences and how when you’re younger you usually develop them.”

What would happen if these innate and developed preferences did not exist? Clearly, we do not give in to every craving. Instead, many of our decisions are based on what nutrition labels and clocks tell us. Whether processing quick bites or full meals, our stomachs are subject to on-demand digestion. Some people may experience a 24/7 urge to consume while others limit themselves to set times in the day. Is one habit better for overall health?

As college students, those feeding schedules long-enforced by parents and lunch bells are now disrupted by a lifestyle filled with not only a long-desired freedom, but also disorder. Lots of it. Interestingly, science seems to explain which feeding pattern—whether around the clock or in regulated intervals—is best.

Illustation by Aimee Ermel

Illustation by Aimee Ermel

Dialing Back on Snack Attacks

To explore this phenomenon, undergraduate student Ishika Arora, working in Dr. Satchidananda Panda’s lab, divided a sample of mice into groups based on two feeding patterns. One group was given food with a high fat content around the clock while the other group was fed the same high fat food for around eight hours a day.

Despite the difference in food access times, the mice consumed the same amount of calories. However, Arora discovered that the mice who ate with a time restriction had normal cholesterol levels and did not become diabetic, compared to their counterparts who were obese and mostly diabetic with extremely high cholesterol levels.

“The whole experiment surprised me. The phenomenon is so amazing with the restricted feeding. It has so much potential in the real world that it could even work for humans,” Arora said.

Theoretically applying her results to humans’ dietary patterns, Arora believes that to become healthier, one just has to limit the time per day that one consumes high fat foods. This lifestyle intervention can be a preventative method to metabolic disease. If an innate preference is telling you to snack on those fried potato chips at midnight and again at three in the morning, it is important to disregard the preference, and focus on an eating time that is better for health purposes.

Greater restriction and reformed eating patterns can greatly reduce the risk of chronic illnesses later in life. Whether among fruit flies or mice, babies or college students, eating habits play an essential role in determining day-to-day schedules and general well-being. It is time to regain control over what nutrients you put inside your body and when you do so. Don’t let your neurons and your marathon study sessions do all the talking—or in this case, all the eating.

Before you reach for that cup of sodium and chemicals that is Top Ramen at two in the morning, pause to think about what’s driving you to make such a decision. In order to eat healthily and responsibly, we must first strive to be intentional about the meals on our plates. In this way, we can indeed eat the way we are.

Writer Information

Brianna Egan is a Biochemistry and Cell Biology major from Sixth College. She will be graduating in 2016. Demiana Sidrak is a Human Biology major from Sixth College. She will be graduating in 2015. An Qi (Angela) Yao is a Human Biology major from Revelle College. She will be graduating in 2013. Alice Zalan is a General Biology major from Thurgood Marshall College. She will be graduating in 2016.



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