“Aw, you still have your baby fat!” This refrain plagued me throughout my childhood. No matter what I did, I couldn’t shake my “baby fat.” I was not a particularly overweight child. I just seemed to maintain the round cheeks and pudgy tummy that most of my friends shed early on. “Oh, sweetheart, don’t worry,” my mother would say, “it will keep you warm. Just a little added insulation.” She wasn’t even half right.
In the years since, I’ve become an anthropologist who studies nutrition, human growth, and development. And, as it turns out, I wasn’t the only one who carried a few extra pounds. Humans are the fattest species on record at birth. A baby human is born with about 15 percent body fat—a higher percentage than any other species in the world. Only a small number of other mammals make it into the double digits at birth: about 11 percent for guinea pigs and around 10 percent for harp seals, for example. Even our nearest primate relatives are not born as fat as we are.
Most of the fat animal babies we think of—seal pups, piglets, and puppies—gain much of their fat after birth. This is true for all of our fellow mammals, whether they are much smaller than us or much larger. But human babies keep on gaining fat too. Infant fatness peaks between 4 and 9 months of age at about 25 percent before it begins a long slow decline. This period of baby fat thinning leads to a stage in childhood when most humans have the lowest body fat percentage they will have in their lives, unless of course you’re one of the not-so-lucky ones. So just why is it that human babies are born with so much fat?
Like my mom, many scholars have proposed that a thick layer of fat helps keep babies warm. But there isn’t much evidence that supports this theory. We don’t observe greater levels of body fat in populations that live in colder climates, and putting on layers of fat doesn’t seem to help us deal with the cold. Fat is critical to our warmth—it just doesn’t serve us by working only as insulation.
There are actually two kinds of fat: white fat, the normal fat we all know and love, and brown fat, also known as “brown adipose tissue,” or BAT. BAT is a special kind of fat that’s present in all neonatal mammals and is especially important in humans, who are unable to raise their body temperature through shivering. BAT generates heat by burning white fat and serves as a baby’s internal “furnace.” As infants and children develop, BAT begins to shrink until there is very little left in adulthood. Unfortunately for my mom, BAT only composes about 5 percent of an infant’s total body fat.
So, if it’s not for warmth, what does all that baby fat do?
Fat is the way that humans and all other mammals store energy. We do this to provide for ourselves during periods of nutritional shortfall, when there isn’t enough food or when food sources are irregular. One of the reasons such stores are so important for humans is that we have an extremely demanding organ that requires a lot of energy: our brain.
A human baby’s brain is massive relative to its body size and is estimated to use around 50 to 60 percent of a baby’s energy budget. That means if there are any shortfalls in energy or if an infant’s nutrition is poor, there can be serious consequences. As such, babies have large energetic reserves in the form of fat deposits that they can use if nutrition is inadequate. High fat at birth is particularly useful for humans, who go through a sort of fasting period after birth while waiting for their mother’s breast milk to come in; the first milk, or colostrum, is packed with protein, vitamins, minerals, and immune boosting antibodies but is lower in sugar and fat content than regular breast milk.
On top of needing to provide for their big, energetically expensive brains, human babies also require energy for growth and for staving off illness. As I mentioned, they continue to grow their fat reserves through the first 4 to 9 months of postnatal life. Interestingly, it is at this stage in their development that infants begin to experience two major issues: an increase in exposures to pathogens that can make them sick—crawling around on the ground, putting literally everything in their mouths—and marginal nutrition. During this phase, the nutrition that mom provides through breastfeeding isn’t enough and has to be supplemented with specially prepared, nutritionally dense foods. While some of us can now acquire manufactured baby foods designed to do just that, such shortcuts weren’t available for the majority of human history. Between increasingly complex nutritional needs and the demand for energy necessary to fight off illness, human babies use their baby fat reserves as an essential energetic buffer for these transition periods, allowing them to feed their brains and continue their growth.
So my pudgy tummy didn’t offer warmth, but I guess my mom was right about one thing: Baby fat isn’t so bad after all.
The Aftermath of Michael Jackson’s Antigravity Lean
The infamous lean.
In Michael Jackson’s 1987 music video “Smooth Criminal,” the legendary performer leans forward 45 degrees from a straight-up position — and comes back. It’s a feat that seemingly defies both physics and physiology, and the move has become another element of MJ’s aura of mystery.
Some type of cinematic or mechanical trick must be responsible, since most people can manage only a 20-degree forward tilt before toppling headlong. Yet Jackson performed the move live on tours around the world for years.
In a study published this week in the Journal of Neurosurgery, three scientists examine the so-called Antigravity Lean, not from a physics but from a physiological perspective. The three neurosurgeons, all at the Postgraduate Institute of Medical Education and Research in Chandigarh, India, combine in the article their knowledge of Jackson with data on spine biomechanics.
It’s been known for years how Jackson defied gravity. His shoes had a slot that slid onto a bolt in the floor, allowing him to perform the dramatic lean.
Bending forward is limited by the erector spinae muscles, which act like cables to support forward bends up to 20 degrees, though some dancers can achieve 30 degrees, the paper says. When near the max of a bend, you can feel the strain on the Achilles’ heel as the ankles become the fulcrum for balance. People soon return to vertical or catch themselves from falling headlong.
Though Jackson’s 45-degree bend is not physically possible without trickery, the King of Pop still needed incredible core strength and leg muscles to pull it off, the authors write. Not just anyone can lock their shoes into the floor and become Michael Jackson, it seems.
“Several MJ fans, including the authors, have tried to copy this move and failed, often injuring themselves in their endeavors,” the researchers write.
Figure A shows the Antigravity Tilt (a 45-degree forward bend) and the normal limit that most people can bend forward. Jackson used shoes with a slot that slid onto a bolt in the floor. Figure B shows the shift when the body’s fulcrum is the hip and when it’s the Achilles’ tendon. (Illustration courtesy of Manjul Tripathi)
Tough Act to Follow
Jackson’s sleight of foot inspired generations of dancers who push the limits physically. This has resulted in spinal stresses not previously seen by neurosurgeons.
This is not to point the finger at Jackson. But it does suggest the reality that injuries can occur that might require implant spinal surgery, the article says, something potentially devastating to a dancer.
But it’s not all bad news — neurosurgeons have gained a lot of new information on how to treat spinal cord injuries in recent years, something that could be in part thanks to MJ’s envelope-pushing dance moves.
“The King of Pop has not only been an inspiration but a challenge to the medical fraternity,” Tripathi says.
Your Emergency Contact Does More Than You Think
You know when you’re filling out your medical paperwork and it asks for your emergency contact? Sure, the process might be annoying, but that emergency contact could actually be put to good use by researchers.
Since many of us use a family member, those contacts can help scientists create family trees. And they can also be used for genetics and disease research, according to a study released Thursday in Cell. Discovering what diseases are inheritable can be a laborious and expensive process — patients must be recruited and researchers must clearly determine patients’ phenotypes (physical traits that include eye color, height, and overall health and are often influenced by your genes).
To make that process easier researchers from three major New York medical centers generated family trees from millions of electronic medical records to create a database.This is the first time electronic health records have been used to trace ancestry and it’s the largest study of heritability using such records.
The More You Know
The researchers identified 7.4 million relatives with an algorithm that matched names, addresses and phone numbers from three medical centers. They found 500 inheritable phenotypes in the data just by looking at test results and observations in health records. The traits included diseases affecting skin, blood and mental health.
The data can help determine the heritability level of many common diseases. For example, researchers found that having an increase of HDL (good) cholesterol is 50 percent heritable, while LDL (bad) cholesterol is only 25 percent heritable. The study’s findings were consistent across the participating medical centers and published studies.
Previous heritability research primarily documented Caucasians of northern European descent, according to the study’s first author Fernanda Polubriaginof, but this research is much broader.
“This dataset will allow us for the first time to compute whether there are differences in other races and ethnicities,” said Polubriaginof in a news release.
Future studies could look at medical records for the hereditary contribution of any trait. Due to privacy issues, patient identifiers were removed for the data, which can only be used for research at the moment. Though, with patient consent, emergency contacts could be put to important use in the future.
Mosquito Bites Leave A Lasting Impression On Our Immune System
Mosquito bites are like a gross form of French kissing — the insects swap your blood with their saliva, and leave a trail of salivary secretions behind like mosquito cooties. Some of those compounds prevent clotting as the insects slurp up your blood. Now researchers find mosquito spit aggravates your immune system for days afterward. The findings could help scientists develop vaccines for mosquito-born diseases like Zika.
Rebecca Rico-Hesse, a virologist at Baylor College of Medicine in Houston, Texas, wanted to know how mosquitoes exploit our immune systems with their drool. So, she and her team exposed mice with human-like immune systems to live mosquitoes. Then, they sized up the mice’s immune response as it reacted to the mosquito spittle.
The bug’s saliva toyed with their immune systems in both bone marrow and skin cells with effects that lasted up to seven days after biting, the team reports today in PLoS: Neglected Tropical Diseases. The researchers say their discovery could explain how these tissues might act as virus incubators and help spread disease.
In 2012, Rico-Hesse was looking to untangle how Dengue virus causes Dengue hemorrhagic fever — an illness that affects 400 million people each year and can lead to death — when she came across a strange occurrence. Mice infected with the virus from mosquito bites fared far worse than mice that had received an injection of the virus but hadn’t been served as a mosquito meal. The result made Rico-Hesse take a step back.
It seems that mosquito bites caused the immune system to behave differently, and in ways that could potentially give infectious diseases a leg up.
To find out, Rico-Hesse and her team set starving Aedes aegypti mosquitoes on mice that had received a dose of human stem cells to make their immune systems look more like a human’s. Each mouse endured eight mosquito bites total. Then the team checked out different parts of the immune system — blood, bone marrow, spleen, and skin cells — six and 24 hours after biting, as well as seven days later. By then, the immune system should have returned to normal.
Instead, the team discovered immune cells that had disappeared from the skin at least six hours post-bite came back seven days later after maturing in bone marrow, something that shouldn’t have happened. If those cells harbored a virus, they could then pass it on to new mosquitoes, who could infect others.
The research is pointing out new ways in which mosquito bites affect our immune systems, and it goes beyond simple itching and scratching.
“Mosquito saliva has evolved to modify our immune system,” Rico-Hesse said. And as their new research shows, viruses and parasites could be hijacking that activity to get to the cells they reproduce in, like bone marrow cells, faster, according to her.
Essentially, viruses might be taking advantage of the immune system’s response to travel from their point of entry — the skin — to a place they can multiply in that’s away from attacks by the immune system.
“It’s mind-blowing,” Rico-Hesse said. “No one has ever seen this before.”
Ultimately, the work could lead to infection-blocking vaccines, said Duane Gubler, an international health expert who was not involved in the research.
That’s what Rico-Hesse hopes, too. “If we can make a vaccine that would protect us against the effects of the [mosquito] saliva, or blocking our immune reaction … then we could stop global vector-born diseases,” she said.
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