Medical News Today: New research may explain why evolution made humans ‘fat’

Scientists have compared fat samples from humans and other primates and found that changes in DNA packaging affected how the human body processes fat.
close up of hand drawing evolution of humans from primates
Evolution made humans the ‘fat primate,’ researchers suggest.

Our bodies need fat to store energy and protect vital organs.

Fat also helps the body absorb some nutrients and produce important hormones.

Dietary fats include saturated fats, trans fats, monounsaturated fats, and polyunsaturated fats, all of which have different properties.

People should try to avoid or only consume saturated and trans fats in moderation because they raise low-density lipoprotein (LDL), or “bad,” cholesterol levels. Monounsaturated and polyunsaturated fats, however, can lower LDL cholesterol levels.

Triglycerides are the most common type of fat in the body. They store excess energy from the food we eat. During digestion, our bodies break these down and transfer them to the cells via the bloodstream. Our bodies use some of this fat as energy and store the rest inside the cells.

Fat metabolism is key to human survival, and any imbalances in the process can lead to obesity, diabetes, and cardiovascular disease.

Cardiovascular disease is the number one cause of death worldwide. The World Health Organization (WHO) estimate that almost 18 million people died from the condition in 2016.

How humans became the ‘fat’ primate

Modern eating habits and a lack of exercise have contributed to the obesity “epidemic,” but new research highlights the role that evolution played in the increasing formation of human body fat.

The scientists found that changes to how DNA is packaged inside fat cells reduced the human body’s ability to turn “bad” fat into “good” fat. The results of the research now appear in the journal Genome Biology and Evolution.

“We’re the fat primates,” says study co-author Devi Swain-Lenz, a postdoctoral associate in biology at Duke University in Durham, NC.

The researchers — who Swain-Lenz and Duke biologist Greg Wray led — compared fat samples from humans, chimps, and other primates using a technique called ATAC-seq. This analyzes how fat cell DNA is packaged in the bodies of different species.

The findings revealed that humans have anywhere from 14% to 31% body fat, while other primates have less than 9%. Also, DNA regions in humans are more condensed, thereby limiting accessibility to the genes involved in fat metabolism.

The researchers also found that around 780 DNA regions were more accessible in chimps and macaques compared with humans. This means that the human body has a reduced capacity to transform bad fat into good fat.

Not all fat is the same

Swain-Lenz explains that most fat is made up of “calorie-storing white fat.” This is the type of fat that accumulates on our bellies and around our waistlines. Other fat cells, called beige and brown fat, help burn calories.

The results of this new study revealed that one of the reasons humans carry more fat is because the DNA regions that should help convert white fat into brown fat are compressed and do not allow this transformation to take place.

“It’s still possible to activate the body’s limited brown fat by doing things like exposing people to cold temperatures, but we need to work for it,” Swain-Lenz adds.

The team believes that early humans may have needed to accumulate fat not just to protect vital organs and warm up, but also to nurture their growing brains. In fact, the human brain tripled in size during evolution, and it now uses more energy than any other organ.

Scientists have been working to understand if promoting the body’s ability to convert white fat to brown fat could reduce obesity, but more research is necessary.

“Maybe we could figure out a group of genes that we need to turn on or off, but we’re still very far from that,” Swain-Lenz concludes.

Medical News Today: Humans can learn new foreign words while asleep

Recent research reveals for the first time that people can learn new information while they are asleep.
woman asleep with book
Learning can also occur during sleep, new research shows.

Scientists already know that sleep consolidates learning of new information that we acquire during wakefulness.

Now, researchers at the University of Bern in Switzerland suggest that learning can also take place during deep, or slow-wave sleep.

In a study that features in the journal Current Biology, they show how associations with new foreign words can occur at certain phases of slow-wave sleep.

Much sleep research concerns the processes that stabilize and consolidate memories that form during periods of wakefulness.

There is now considerable evidence that replay during sleep strengthens memories and embeds them in the previously acquired knowledge store in the brain.

The study authors note that many deem it impossible that learning can take place during sleep because “sleep lacks the conscious awareness” and the necessary brain chemistry and activity.

In addition, studies that have examined sleep learning in humans have yielded conflicting results.

Learning during daytime naps

The researchers were intrigued by the question: If the sleep state strengthens a “memory trace” that forms during wakefulness, then why can’t the sleep state itself form a memory trace that endures into wakefulness?

Using electroencephalograms (EEGs), they recorded brainwave activity in 41 healthy male and female volunteers as they took a daytime nap and while they underwent subsequent memory tests.

During the nap, the volunteers also wore in-ear headphones through which the researchers played recordings of numerous verbal word pairs.

They devised each word pair so that one word was a familiar, native-language word while the other was a made-up “pseudoword.”

For example, they paired the word “house” with the pseudoword “tofer.” In another pair, the familiar word was “cork,” and the pseudoword was “aryl.”

After the nap, the volunteers underwent a test of their “sleep-formed associations.”

The test presented them with random samples of the pseudowords. At each presentation, they had to say whether the object the word described could fit inside a shoebox or not.

The results showed that the size classification of the pseudowords was better than chance if the “acoustic presentation of the second word of a pair during sleep repeatedly hit an ongoing slow-wave peak.”

Timing of encoding is key

Slow-wave, or deep sleep is the most beneficial stage for consolidating memories that form in the period of wakefulness that precedes it.

As the brain enters slow-wave sleep, its cells gradually synchronize their activity. They fall into a pattern that alternates every 0.5 seconds between brief periods of universal activity and inactivity. Periods of activity appear as peaks on EEGs.

The researchers found that the volunteers only encoded the association between a sleep-played, familiar, native-language word and its pseudoword under two conditions.

The first condition was repetition of the word pair, and the second condition was that the acoustic presentation of the second word had to coincide with an active phase of slow-wave sleep.

In other words, the volunteers were better able to correctly classify “tofer” as being too large to fit into a shoebox if they had heard the word pair “house-tofer” several times, and the second word had occurred while their brain cells were in an active phase of slow-wave sleep.

Co-first study author Marc Züst, Ph.D., says that they also observed that retrieval of sleep-learned words during the test coincided with activity in the hippocampus and language areas of the brain. The hippocampus plays a key role in memory and learning.

These are the same brain areas that are active when learning occurs during wakefulness.

These brain structures appear to mediate memory formation independently of the prevailing state of consciousness — unconscious during deep sleep, conscious during wakefulness.”

Marc Züst, Ph.D.