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How your brain makes you overeat
Turns out the more we desire a food, the more we have to consume to feel satiated.
- The brain's reward system releases dopamine when tasting food.
- Researchers at Max Planck discovered a second dopamine release in the stomach, affecting higher cognitive functions.
- The more we desire a food, the weaker the second release, which might lead to overeating.
As if losing weight wasn't hard enough. A new study from researchers at the Max Planck Institute for Metabolism Research reveals that we're rewarded twice when eating. The first dopamine kick occurs when tasting food; the second, when the food reaches your stomach.
Making this process even more insidious, the more you crave the food, the less dopamine is produced by your stomach, which the researchers believe might lead to overeating.
Previous research has shown that even thinking about food starts the process of salivation by releasing a protein enzyme, amylase, which helps break down food before it reaches your stomach. Interestingly, if you head to your favorite restaurant and they're out of the dish you've been craving, the emotional discontent is real. Your brain has been tricked—well, your brain tricked itself.
For this study, the researchers write that pleasant taste and nutritional value are both reinforcers for consuming certain foods. Yet the desire for a gustatory-pleasing experience overrides health concerns. They point to research highlighting the brain's dopaminergic system as the key mediator in overeating. In simple terms: If we like it, we eat it, and keep eating it beyond the point of satiation.
As the team puts it:
Highly processed food with added fat and sugar is known to include higher food wanting and overconsumption.
This has been expressed in evolutionary terms elsewhere. Sweet and fats were rare throughout most of history. When our ancestors discovered them, they gorged. Now, at a time when the entirety of taste profiles and nutrients are a few swipes on your phone away, the dopaminergic system hasn't caught up to the news that we don't need all those tastes all the time. Dopamine keeps us swiping.
To test the physiological reasons for this, the team at Max Planck recruited 12 normal-weight male volunteers (average age, 56) to drink either a milkshake or a tasteless chemistry experiment in a glass. They then performed PET (positive emission topography) scans on their brains. Lead researcher, Marc Tittgemeyer, explains the results:
With the help of a new position emission topography technique we developed, we were not only able to find the two peaks of dopamine release, but we could also identify the specific brain regions that were associated with these releases.
The first release, as expected, occurred in the reward system. They identified dopamine release in the lateral hypothalamus and dorsal striatum, as well as the orosensory pathways, mesolimbic dopamine system, and regions associated with reward value signaling, memory, and inhibition control. This complex interplay of regions connects desire with continual consumption, especially those last two regions, the hippocampus and lateral ventral anterior nucleus of the thalamus.
The second dopamine release occurred 15-20 minutes later, when the milkshake was in their stomachs. These higher cognitive function regions include the anterior insula, ventral posterior medial nucleus of the thalamus (again), caudate nucleus, palladium, and amygdala, among others. Basically, the brain was being told that a) everything is all good and b) I like it.
The strangest result was the fact that the more a volunteer craved the milkshake, the less dopamine was produced in the second stage. As study co-author, Heiko Backes, states:
On one hand, dopamine release mirrors our subjective desire to consume a food item. On the other hand, our desire seems to suppress gut-induced dopamine release.
The researchers agree that this might be the physiological reason we overeat. As with many drugs, we desire the feeling we originally received when first consuming the food. The stronger the desire, the less effective it is. Our response is to keep returning in hopes of chasing down that initial feeling.
Of course, 12 men drinking milkshakes is just the beginning of this research, but fascinating at that. The more we understand why we overeat, the closer we are to finding solutions.
Certain water beetles can escape from frogs after being consumed.
- A Japanese scientist shows that some beetles can wiggle out of frog's butts after being eaten whole.
- The research suggests the beetle can get out in as little as 7 minutes.
- Most of the beetles swallowed in the experiment survived with no complications after being excreted.
In what is perhaps one of the weirdest experiments ever that comes from the category of "why did anyone need to know this?" scientists have proven that the Regimbartia attenuata beetle can climb out of a frog's butt after being eaten.
The research was carried out by Kobe University ecologist Shinji Sugiura. His team found that the majority of beetles swallowed by black-spotted pond frogs (Pelophylax nigromaculatus) used in their experiment managed to escape about 6 hours after and were perfectly fine.
"Here, I report active escape of the aquatic beetle R. attenuata from the vents of five frog species via the digestive tract," writes Sugiura in a new paper, adding "although adult beetles were easily eaten by frogs, 90 percent of swallowed beetles were excreted within six hours after being eaten and, surprisingly, were still alive."
One bug even got out in as little as 7 minutes.
Sugiura also tried putting wax on the legs of some of the beetles, preventing them from moving. These ones were not able to make it out alive, taking from 38 to 150 hours to be digested.
Naturally, as anyone would upon encountering such a story, you're wondering where's the video. Thankfully, the scientists recorded the proceedings:
The Regimbartia attenuata beetle can be found in the tropics, especially as pests in fish hatcheries. It's not the only kind of creature that can survive being swallowed. A recent study showed that snake eels are able to burrow out of the stomachs of fish using their sharp tails, only to become stuck, die, and be mummified in the gut cavity. Scientists are calling the beetle's ability the first documented "active prey escape." Usually, such travelers through the digestive tract have particular adaptations that make it possible for them to withstand extreme pH and lack of oxygen. The researchers think the beetle's trick is in inducing the frog to open a so-called "vent" controlled by the sphincter muscle.
"Individuals were always excreted head first from the frog vent, suggesting that R. attenuata stimulates the hind gut, urging the frog to defecate," explains Sugiura.
For more information, check out the study published in Current Biology.
The design of a classic video game yields insights on how to address global poverty.
Poverty can be a self-sustaining cycle that might require an external influence to break it. A new paper published in Nature Sustainability and written by professor Andrew Bell of Boston University suggests that we could improve global anti-poverty and economic development systems by turning to an idea in a video game about a race car-driving Italian plumber.
A primer on Mario Kart
For those who have not played it, Mario Kart is a racing game starring Super Mario and other characters from the video game franchise that bears his name. Players race around tracks collecting power-ups that can directly help them, such as mushrooms that speed up their karts, or slow down other players, such as heat-seeking turtle shells that momentarily crash other karts.
The game is well known for having a mechanism known as "rubber-banding." Racers in the front of the pack get wimpy power-ups, like banana peels to slip up other karts, while those toward the back get stronger ones, like golden mushrooms that provide extra long speed boosts. The effect of this is that those in the back are pushed towards the center, and those in front don't get any boosts that would make catching them impossible.
If you're in last, you might get the help you need to make a last-minute break for the lead. If you're in first, you have to be on the lookout for these breakouts (and the ever-dreaded blue shells). The game remains competitive and fun.
Rubber-banding: A moral and economic lesson from Mario Kart
In the real world, we see rubber-banding used all the time. Welfare systems tend to provide more aid to those who need it than those who do not. Many of them are financed by progressive taxation, which is heavier on the well-off than the down-and-out. Some research suggests that these do work, as countries with lower levels of income inequality have higher social mobility levels.
It is a little more difficult to use rubber-banding in real life than in a video game, of course. While in the game, it is easy to decide who is doing well and who is not, things can be a little more muddled in reality. Furthermore, while those in a racing game are necessarily antagonistic to each other, real systems often strive to improve conditions for everybody or to reach common goals.
As Bell points out, rubber-banding can also be used to encourage sustainable, growth programs that help the poor other than welfare. They point out projects such as irrigation systems in Pakistan or Payments for Ecosystems Services (PES) schemes in Malawi, which utilize positive feedback loops to both provide aid to the poor and promote stable systems that benefit everyone.
Rubber-banding feedback loops in different systems. Mario Kart (a), irrigation systems in Pakistan (b), and PES operations in Malawi (c) are shown. Links between one better-off (blue) and one worse-off (red) individual are highlighted. Feedback in Mario Kart (a), designed to balance the racers, imprAndrew Bell/ Nature Sustainability
In the Malawi case, farmers were paid to practice conservation agriculture to reduce the amount of sediment from their farms flowing into a river. This immediately benefits hydroelectric producers and their customers but also provides real benefits to farmers in the long run as their soil doesn't erode. By providing an incentive to the farmers to conserve the soil, a virtuous cycle of conservation, soil improvement, and improved yields can begin.
While this loop differs from the rubber-banding in Mario, the game's approach can help illustrate the benefits of rubber-banding in achieving a more equitable world.
The task now, as Bell says in his paper, is to look at problems that exist and find out "what the golden mushroom might be."
Satellite imagery can help better predict volcanic eruptions by monitoring changes in surface temperature near volcanoes.
- A recent study used data collected by NASA satellites to conduct a statistical analysis of surface temperatures near volcanoes that erupted from 2002 to 2019.
- The results showed that surface temperatures near volcanoes gradually increased in the months and years prior to eruptions.
- The method was able to detect potential eruptions that were not anticipated by other volcano monitoring methods, such as eruptions in Japan in 2014 and Chile in 2015.
How can modern technology help warn us of impending volcanic eruptions?
One promising answer may lie in satellite imagery. In a recent study published in Nature Geoscience, researchers used infrared data collected by NASA satellites to study the conditions near volcanoes in the months and years before they erupted.
The results revealed a pattern: Prior to eruptions, an unusually large amount of heat had been escaping through soil near volcanoes. This diffusion of subterranean heat — which is a byproduct of "large-scale thermal unrest" — could potentially represent a warning sign of future eruptions.
Conceptual model of large-scale thermal unrestCredit: Girona et al.
For the study, the researchers conducted a statistical analysis of changes in surface temperature near volcanoes, using data collected over 16.5 years by NASA's Terra and Aqua satellites. The results showed that eruptions tended to occur around the time when surface temperatures near the volcanoes peaked.
Eruptions were preceded by "subtle but significant long-term (years), large-scale (tens of square kilometres) increases in their radiant heat flux (up to ~1 °C in median radiant temperature)," the researchers wrote. After eruptions, surface temperatures reliably decreased, though the cool-down period took longer for bigger eruptions.
"Volcanoes can experience thermal unrest for several years before eruption," the researchers wrote. "This thermal unrest is dominated by a large-scale phenomenon operating over extensive areas of volcanic edifices, can be an early indicator of volcanic reactivation, can increase prior to different types of eruption and can be tracked through a statistical analysis of little-processed (that is, radiance or radiant temperature) satellite-based remote sensing data with high temporal resolution."
Temporal variations of target volcanoesCredit: Girona et al.
Although using satellites to monitor thermal unrest wouldn't enable scientists to make hyper-specific eruption predictions (like predicting the exact day), it could significantly improve prediction efforts. Seismologists and volcanologists currently use a range of techniques to forecast eruptions, including monitoring for gas emissions, ground deformation, and changes to nearby water channels, to name a few.
Still, none of these techniques have proven completely reliable, both because of the science and the practical barriers (e.g. funding) standing in the way of large-scale monitoring. In 2014, for example, Japan's Mount Ontake suddenly erupted, killing 63 people. It was the nation's deadliest eruption in nearly a century.
In the study, the researchers found that surface temperatures near Mount Ontake had been increasing in the two years prior to the eruption. To date, no other monitoring method has detected "well-defined" warning signs for the 2014 disaster, the researchers noted.
The researchers hope satellite-based infrared monitoring techniques, combined with existing methods, can improve prediction efforts for volcanic eruptions. Volcanic eruptions have killed about 2,000 people since 2000.
"Our findings can open new horizons to better constrain magma–hydrothermal interaction processes, especially when integrated with other datasets, allowing us to explore the thermal budget of volcanoes and anticipate eruptions that are very difficult to forecast through other geophysical/geochemical methods."