It is widely accepted that being overweight definitely poses a danger to our health. According to a new study, obesity may even damage the brain’s ability to recognize the sensation of fullness and be satisfied after eating fats and sugars.

Further, those brain changes may last even after people considered medically obese lose a significant amount of weight — possibly explaining why many people often regain the pounds they lose.

The study, published Monday in Nature Metabolism, was a controlled clinical trial in which 30 people considered to be medically obese and 30 people of normal weight were fed sugar carbohydrates (glucose), fats (lipids) or water (as a control). Each group of nutrients was fed directly into the stomach via a feeding tube on separate days.

The night before the testing, all 60 study participants had the same meal for dinner at home and did not eat again until the feeding tube was in place the next morning. As either sugars or fats entered the stomach via the tube, researchers used functional magnetic resonance(磁共振) imaging and single-photon emission computed tomography(断层扫描技术) to capture the brain’s response over 30 minutes.

In people with normal weight, the study found brain signals in the striatum(纹状体) slowed when either sugars or fats were put into the digestive system — evidence that the brain recognized the body had been fed. At the same time, levels of dopamine rose in those at normal weight, signaling that the reward centers of the brain were also activated. However, when the same nutrients were given via feeding tube to people considered medically obese, brain activity did not slow, and dopamine levels did not rise.

Next, the study asked people with obesity to lose 10% of their body weight within three months — an amount of weight known to improve blood sugars, reset metabolism and boost overall health.

Tests were repeated as before — with surprising results. Losing weight did not reset the brain in people with obesity.

Much more research is needed to fully understand what obesity does to the brain, and if that is triggered by the fat tissue itself, the types of food eaten, or other environmental and genetic factors.

Human societies developed food preferences based on what was available and what the group decided it liked most. Those preferences were then passed along as socially learned behaviors, values, knowledge and customs that make up culture. Besides humans, many other social animals are believed to exhibit forms of culture in various ways, too.

In fact, according to a new study led by Harvard scientist Liran Samuni, bonobos(倭黑猩猩), one of our closest living relatives, could be the latest addition to the list.

The researchers studied the hunting and feeding habits of two neighboring groups of bonobos in the Democratic Republic of Congo. Analyzing the data, they saw many similarities in the lives of the two bonobo groups—the Ekalakala and the Kokoalongo. They also both have the access and opportunity to hunt the same kind of prey(猎物). This, however, is precisely where researchers noticed a striking difference.

The groups consistently preferred to hunt and feast on two different types of prey. The Ekalakala group went after an anomalure(鳞尾松鼠). The Kokoalongo group on the other hand, favored a duiker(小羚羊).

“It’s basically like two human cultures exploiting a common resource in different ways,” says Samuni. “Think about two cultures living close to each other but having different preferences: One prefers chicken while the other is more of a beef-eating culture.”

Using statistical modeling, the researchers found that the only variable that could reliably predict prey preference was whether the hunters were team Ekalakala or team Kokoalongo.

The researchers haven't yet investigated how the bonobo groups learned this hunting preference, but through their analysis they were able to rule out ecological factors or genetic differences. Basically, it means all evidence points toward this being a learned social behavior.

“If our closest living relatives have some cultural traits(特征), then it's likely our ancestors already had some capacity for culture,” Samuni says.

Being highly connected to a strong social network has its benefits. Now a new study is showing the same goes for trees, thanks to their underground neighbors. The study is the first to show that the growth of adult trees is linked to their participation in fungal networks living in the forest soil. Though past research has focused on young trees, these findings give new insight into the significance of fungal networks to older trees — which are more environmentally beneficial for functions like capturing carbon.

“Large trees make up the main part of the forest, so they drive what the forest is doing,” said researcher Joseph Birch, who led the study. When they live in the forest soil, fungal networks act as a sort of highway, allowing water, nutrients and compounds to flow back and forth among the trees. The network also helps nutrients flow to resource - limited trees like family units that support one another in times of stress.

Cores taken from 350 Douglas firs (花旗松) showed that annual tree ring growth was related to the extent of fungal connections a tree had with other trees. They had much higher growth than those that had only a few connections. The research also showed that trees with more connections to many unique fungi had much greater growth than those with only one or two connections. “If you have this network that is helping trees grow faster, that helps capture more carbon year after year. These networks may help trees grow more steadily even as conditions become more stressful, and could even help protect them against death.” said Birch.

Birch hopes his findings lead to further studies in different kinds of forests in other geographical areas, because it's likely that the connections among trees change from year to year. He said, “Knowing whether fungal networks are operating the same way in other tree species could factor into how we reforest areas after harvesting them, and it could inform how we want to plant trees to preserve these networks.”