Chapter 9. Homeostasis: Active Regulation of the Internal Environment
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By ANAHAD O’CONNOR People who avoid carbohydrates and eat more fat, even saturated fat, lose more body fat and have fewer cardiovascular risks than people who follow the low-fat diet that health authorities have favored for decades, a major new study shows. The findings are unlikely to be the final salvo in what has been a long and often contentious debate about what foods are best to eat for weight loss and overall health. The notion that dietary fat is harmful, particularly saturated fat, arose decades ago from comparisons of disease rates among large national populations. But more recent clinical studies in which individuals and their diets were assessed over time have produced a more complex picture. Some have provided strong evidence that people can sharply reduce their heart disease risk by eating fewer carbohydrates and more dietary fat, with the exception of trans fats. The new findings suggest that this strategy more effectively reduces body fat and also lowers overall weight. The new study was financed by the National Institutes of Health and published in the Annals of Internal Medicine. It included a racially diverse group of 150 men and women — a rarity in clinical nutrition studies — who were assigned to follow diets for one year that limited either the amount of carbs or fat that they could eat, but not overall calories. “To my knowledge, this is one of the first long-term trials that’s given these diets without calorie restrictions,” said Dariush Mozaffarian, the dean of the Friedman School of Nutrition Science and Policy at Tufts University, who was not involved in the new study. “It shows that in a free-living setting, cutting your carbs helps you lose weight without focusing on calories. And that’s really important because someone can change what they eat more easily than trying to cut down on their calories.” © 2014 The New York Times Company
Link ID: 20018 - Posted: 09.02.2014
By CARL ZIMMER Your body is home to about 100 trillion bacteria and other microbes, collectively known as your microbiome. Naturalists first became aware of our invisible lodgers in the 1600s, but it wasn’t until the past few years that we’ve become really familiar with them. This recent research has given the microbiome a cuddly kind of fame. We’ve come to appreciate how beneficial our microbes are — breaking down our food, fighting off infections and nurturing our immune system. It’s a lovely, invisible garden we should be tending for our own well-being. But in the journal Bioessays, a team of scientists has raised a creepier possibility. Perhaps our menagerie of germs is also influencing our behavior in order to advance its own evolutionary success — giving us cravings for certain foods, for example. “One of the ways we started thinking about this was in a crime-novel perspective,” said Carlo C. Maley, an evolutionary biologist at the University of California, San Francisco, and a co-author of the new paper. “What are the means, motives and opportunity for the microbes to manipulate us? They have all three.” The idea that a simple organism could control a complex animal may sound like science fiction. In fact, there are many well-documented examples of parasites controlling their hosts. Some species of fungi, for example, infiltrate the brains of ants and coax them to climb plants and clamp onto the underside of leaves. The fungi then sprout out of the ants and send spores showering onto uninfected ants below. How parasites control their hosts remains mysterious. But it looks as if they release molecules that directly or indirectly can influence their brains. © 2014 The New York Times Company
|By Melinda Wenner Moyer For most people, “fat,” particularly the kind that bulges under the skin, is a four-letter word. It makes our thighs jiggle; it lingers despite our torturous attempts to eliminate it. Too much of it increases our risk for heart disease and type 2 diabetes (the most common form of the condition). For decades researchers have looked for ways to reduce our collective stores of fat because they seemed to do more harm than good. But biology is rarely that simple. In the late 2000s several research groups independently discovered something that shattered the consensus about the absolute dangers of body fat. Scientists had long known that humans produce at least two types of fat tissue—white and brown. Each white fat cell stores energy in the form of a single large, oily droplet but is otherwise relatively inert. In contrast, brown fat cells contain many smaller droplets, as well as chestnut-colored molecular machines known as mitochondria. These organelles in turn burn up the droplets to generate heat. Babies, who have not yet developed the ability to shiver to maintain their body temperature, rely on thermogenic deposits of brown fat in the neck and around the shoulders to stay warm. Yet investigators assumed that all brown fat disappears during childhood. The new findings revealed otherwise. Adults have brown fat, too. Suddenly, people started throwing around terms like holy grail to describe the promise of brown fat to combat obesity. The idea was appealingly simple: if researchers could figure out how to incite the body to produce extra brown fat or somehow rev up existing brown fat, a larger number of calories would be converted into heat, reducing deposits of white fat in the process. © 2014 Scientific American
Link ID: 19953 - Posted: 08.13.2014
James Gorman Deep in the mouse brain, scientists recently found that a very small network of cells, a few thousand at most, turns appetite on and off. They used the most sophisticated of modern techniques, but as has often happened in science — witness penicillin, Velcro and Viagra — the researchers discovered something they weren’t looking for. “This was an accidental discovery,” said David Anderson, of the California Institute of Technology, the senior scientist on the team that reported the finding, in Nature Neuroscience. The discovery may eventually lead to a better understanding and treatment of eating disorders. The surprise and drama of the finding are immediately clear, however, in lab videos. A mouse busily munches lab chow until a light signal is sent to its brain, and the mouse wanders off, no longer interested in food. His lab had previously studied this small group of neurons, in a part of the brain called the amygdala. That earlier research was on fear, an emotion strongly associated with the amygdala in both mice and humans. As a technique called optogenetics became more and more refined, he said, it seemed worth revisiting the neurons with this new tool. Optogenetics requires genetic manipulation of specific cells to make them sensitive to light in a certain wavelength, in this case blue light. Then fiber-optic cables are inserted into the brain, and when the light is turned on, neurons can be activated or turned off. Researchers in Dr. Anderson’s lab, including Haijiang Cai, a postdoctoral researcher and a co-author of the report, prepared the mice and conducted the experiment with the entirely unexpected result. © 2014 The New York Times Company
Link ID: 19945 - Posted: 08.12.2014
The gurgles made by a hungry belly are familiar to us all, but they are not just the side effect of an empty stomach. Brain cells not normally associated with communication send out a signal when they detect blood glucose levels are running low, and this triggers the stomach contractions. Richard Rogers of the Pennington Biomedical Research Center at Louisiana State University and colleagues used a drug called fluorocitrate to knock out the function of certain astrocytes and neurons in the brains of rats, blocking the sensation of hunger. Only when astrocyte function was restored did the gastric grumbles return, showing that it is these cells that respond to low glucose levels (Journal of Neuroscience, DOI: 10.1523/JNEUROSCI.1406-14.2014). The feeling of discomfort you get when hungry is called "hypoglycaemia awareness". "For most people this is only slightly unpleasant, but for diabetics whose glucose levels can drop significantly, [being hungry] can be dangerous," says Rogers. "It's important to understand how this mechanism works." © Copyright Reed Business Information Ltd.
Sarah C. P. Williams Every fall, grizzly bears pack on the pounds in preparation for their winter hibernation. In humans, such extreme weight gain would likely lead to diabetes or other metabolic diseases, but the bears manage to stay healthy year after year. Their ability to remain diabetes-free, researchers have now discovered, can be chalked up to the shutting down of a protein found in fat cells. The discovery could lead to new diabetes drugs that turn off the same pathway in humans. The findings are “provocative and interesting,” says biologist Sandy Martin of the University of Colorado, Denver, who was not involved in the new work. “They found a natural solution to a problem that we haven’t been able to solve.” As people gain weight, fat, liver, and muscle cells typically become less sensitive to the hormone insulin—which normally helps control blood sugar levels—and insulin levels rise. In turn, that increased insulin prevents the breakdown of fat cells, causing a vicious cycle that can lead to full-blown insulin resistance, or diabetes. Developing new diabetes drugs has been hampered by the fact that findings from many mouse models of diabetes have not translated to humans. So Kevin Corbit, a senior scientist at Thousand Oaks, California–based drug company Amgen, decided to start looking at obesity and metabolic disease in other animals. “When I was thinking about things that are quite fat, one of the first things I thought of was bears, and what they do to prepare to go into hibernation,” he says. “But of course you don’t see bears running around with diabetes and heart disease.” © 2014 American Association for the Advancement of Science
Link ID: 19919 - Posted: 08.06.2014
By Smitha Mundasad Health reporter, BBC News Scientists have discovered a central hub of brain cells that may put the brakes on a desire to eat, a study in mice shows. And switching on these neurons can stop feeding immediately, according to the Nature Neurosciences report. Researchers say the findings may one day contribute to therapies for obesity and anorexia. Experts say this sheds light on the many complex nerve circuits involved in appetite control. Scientists from the California Institute of Technology suggest the nerve cells act as a central switchboard, combining and relaying many different messages in the brain to help reduce food intake. Using laser beams they were able to stimulate the neurons - leading to a complete and immediate stop to food consumption. Prof David Anderson, lead author of the study told the BBC: "It was incredibly surprising. "It was like you could just flick a switch and prevent the animals from feeding." Researchers then used chemicals to mimic a variety of scenarios - including feelings of satiety, malaise, nausea and a bitter taste. They found the neurons were active in all situations, suggesting they may be integral in the response to many diverse stimuli. BBC © 2014
Link ID: 19887 - Posted: 07.28.2014
Obese women may have a "food learning impairment" that could explain their attitude to food, research from Yale School of Medicine suggests. Tests on groups of obese and healthy-weight people found that the obese women performed worst when asked to remember a sequence of food picture cards. Writing in Current Biology, Yale researchers tested 135 men and women. The findings could lead to new ways to tackle obesity, the study says. Study author Ifat Levy, assistant professor at Yale School of Medicine, said the difference in the performance of the obese women compared with the other groups was "really striking" and "significant". The tests looked at an individual's ability to learn and predict the appearance of pictures of food or money on coloured cards. The participants were told they would be given whatever appeared on these "reward" cards. In the first phase, the reward cards always followed a particular coloured card in a sequence. Later, the order was changed and the reward cards appeared following a different coloured card. During this time, participants were asked to predict the likelihood of a reward card appearing as the cards were shown one by one. The results showed that obese women performed worst because they overestimated how often the pictures of food, including pretzels or chocolate, appeared. Even after researchers had accounted for other factors, there was still a large difference in their learning performance. Prof Levy said: "This is not a general learning impairment, as obese women had no problem learning when the reward was money rather than food. BBC © 2014
By GRETCHEN REYNOLDS Sleep is essential for good health, as we all know. But a new study hints that there may be an easy but unrealized way to augment its virtues: lower the thermostat. Cooler bedrooms could subtly transform a person’s stores of brown fat — what has lately come to be thought of as “good fat” — and consequently alter energy expenditure and metabolic health, even into daylight hours. Until recently, most scientists thought that adults had no brown fat. But in the past few years, scanty deposits — teaspoonfuls, really — of the tissue have been detected in the necks and upper backs in many adults. This is important because brown fat, unlike the more common white stuff, is metabolically active. Experiments with mice have shown that it takes sugar out of the bloodstream to burn calories and maintain core temperature. A similar process seems to take place in humans. For the new study, published in June in Diabetes, researchers affiliated with the National Institutes of Health persuaded five healthy young male volunteers to sleep in climate-controlled chambers at the N.I.H. for four months. The men went about their normal lives during the days, then returned at 8 every evening. All meals, including lunch, were provided, to keep their caloric intakes constant. They slept in hospital scrubs under light sheets. For the first month, the researchers kept the bedrooms at 75 degrees, considered a neutral temperature that would not prompt moderating responses from the body. The next month, the bedrooms were cooled to 66 degrees, a temperature that the researchers expected might stimulate brown-fat activity (but not shivering, which usually begins at more frigid temperatures). The following month, the bedrooms were reset to 75 degrees, to undo any effects from the chillier room, and for the last month, the sleeping temperature was a balmy 81 degrees. Throughout, the subjects’ blood-sugar and insulin levels and daily caloric expenditures were tracked; after each month, the amount of brown fat was measured. © 2014 The New York Times Company
Link ID: 19844 - Posted: 07.17.2014
by Azeen Ghorayshi Food could be a new weapon in shaking off the effects of jet lag after research in mice showed that the insulin released as a result of eating can be a key factor in restoring a disrupted body clock. Miho Sato and her colleagues at The Research Institute for Time Studies at Yamaguchi University in Japan did experiments in mice and tissue cultures to show, for the first time, that increases in insulin affect circadian rhythms. These daily rhythms affect alertness, sleep patterns, and mediate many other physiological processes. Your biological clock is regulated by two broad factors: first, the central rhythm is reset daily by light, as sensory input from the eyes is processed by a small part of the brain called the suprachiasmatic nucleus. The rise and fall of hormones linked to sleep, for example, match this rhythm. But circadian rhythms are also present in peripheral "clocks" in a wide range of cell types in the body. Some of these can be influenced by food. Sato demonstrated the role of insulin by shifting the peripheral body clock in the livers of mice by feeding them only at night. They then split the mice into two groups, supressed insulin levels in one group, and returned all the mice to daytime feeding. Four days later, the livers of the non-supressed mice had readjusted to a normal daily rhythm, as revealed by the daily rise and fall of liver-gene expression. The livers of the insulin-suppressed mice had still not returned to normal. © Copyright Reed Business Information Ltd.
Keyword: Biological Rhythms
Link ID: 19830 - Posted: 07.15.2014
By Sharon Oosthoek, CBC News Mounting evidence that gut bacteria affect mood and behaviour has researchers investigating just how much power these tiny microbes wield over our mental health. "Many people with chronic intestinal conditions also have psychological disturbances and we never understood why," says McMaster University gastroenterologist Dr. Stephen Collins. Now, scientists such as Dr. Collins are starting to come up with answers. Our lower gastrointestinal tract is home to almost 100 trillion microorganisms, most of which are bacteria. They are, by and large, "good" bacteria that help us digest food and release the energy and nutrients we need. They also crowd out bacteria that can trigger disease. But when things go awry in our guts, they can also go awry in our brains. Up to 80 per cent of people with irritable bowel syndrome experience increased anxiety and depression. And those with autism — a syndrome associated with problems interacting with others — are more likely to have abnormal levels of gut bacteria. Dr. Collins and fellow McMaster gastroenterologist Premysl Bercik have done some of the seminal research into the bacteria-brain-behaviour connection. In a study published last year, they changed the behaviour of mice by giving them fecal transplants of intestinal bacteria. It involved giving adventurous mice bacteria from timid ones, thereby inducing timid behaviour. Before the transplant, adventurous mice placed in a dark, protected enclosure spent much of their time exploring an attached bright, wide-open area. After the transplant, they rarely ventured beyond their enclosure. © CBC 2014
by Helen Thomson You are what your grandmother ate, potentially, but maybe not what your great grandmother consumed. A study in mice shows that undernourishment during pregnancy increases the chances that the next two generations will develop obesity and diabetes. But by then the slate is wiped clean. If the same holds true for humans, it may mean that stressful events in our lives affect our grandchildren's health, but not great-grandchildren. Environmental stresses cause chemical changes to DNA that turn genes on and off. Many researchers believe that these changes can be passed down through sperm and eggs – a mechanism known as epigenetic inheritance. Low-calorie diet For example, studies have linked pregnant mothers that were undernourished during the second world war with gene changes in their children that put them at higher risk of becoming obese or getting cancer. But what happens to later generations is not clear. To model this effect, Anne Ferguson-Smith at the University of Cambridge and her colleagues fed pregnant mice a diet containing 50 per cent fewer calories than usual from the 12th day of gestation until the birth, which is normally after about 20 days. Offspring were smaller than average and developed diabetes when fed a healthy diet. When the male pups had offspring, they were also at higher risk of becoming diabetic. The team analysed the sperm of the offspring from the undernourished mothers to see how many genes had had their expression altered by the addition or removal of a methyl group – an epigenetic change. The team found a decrease in methylation in 111 regions of the DNA compared with sperm from mice born to mothers fed a healthy diet. © Copyright Reed Business Information Ltd
Erika Check Hayden Nearly 750,000 babies born each year in the United Kingdom are at risk of brain damage because of low oxygen during birth. Cooling babies who are at risk of brain damage provides long-lasting prevention of such injuries, researchers report today in the New England Journal of Medicine1. A team led by Denis Azzopardi, a neonatologist at King’s College London, lowered the body temperature of 145 full-term babies who were born after at least 36 weeks of gestation. All were at risk of brain damage because they had been deprived of oxygen during birth — a problem that is often caused by troubles with the placenta or umbilical cord, and affects nearly 750,000 babies a year in the United Kingdom. The researchers cooled the infants to between 33°C and 34°C for 72 hours, starting within 6 hours of birth. The technique is known to boost the chances that children avoid brain damage until they become toddlers2, but any longer-term benefits have remained unclear. The study finds treated babies had better mental and physical health than untreated infants through to ages 6 or 7: they were 60% more likely to have normal intelligence, hearing and vision. Those who survived to childhood also had fewer disabilities such as difficulty walking and seeing. "The bottom line is that this doubles a child’s chance of normal survival," says David Edwards, a neonatologist at King’s College London and an author of the study. Neonatologist David Rowitch from the University of California, San Francisco, who studies treatments for paediatric brain damage, says the new findings are important because they show sustained improvements. "This study is encouraging, adding to the weight of evidence showing both positive early indicators and also school-age benefits to hypothermia," Rowitch adds. © 2014 Nature Publishing Group,
Keyword: Development of the Brain
Link ID: 19814 - Posted: 07.10.2014
Adults with extreme obesity have increased risks of dying at a young age from cancer and many other causes including heart disease, stroke, diabetes, and kidney and liver diseases, according to results of an analysis of data pooled from 20 large studies of people from three countries. The study, led by researchers from the National Cancer Institute (NCI), part of the National Institutes of Health, found that people with class III (or extreme) obesity had a dramatic reduction in life expectancy compared with people of normal weight. The findings appeared July 8, 2014, in PLOS Medicine. “While once a relatively uncommon condition, the prevalence of class III, or extreme, obesity is on the rise. In the United States, for example, six percent of adults are now classified as extremely obese, which, for a person of average height, is more than 100 pounds over the recommended range for normal weight,” said Cari Kitahara, Ph.D., Division of Cancer Epidemiology and Genetics, NCI, and lead author of the study. “Prior to our study, little had been known about the risk of premature death associated with extreme obesity.” In the study, researchers classified participants according to their body mass index (BMI), which is a measure of total body fat and is calculated by dividing a person’s weight in kilograms by their height in meters squared. The 20 studies that were analyzed included adults from the United States, Sweden and Australia. These groups form a major part of the NCI Cohort Consortium, which is a large-scale partnership that identifies risk factors for cancer death. After excluding individuals who had ever smoked or had a history of certain diseases, the researchers evaluated the risk of premature death overall and the risk of premature death from specific causes in more than 9,500 individuals who were class III obese and 304,000 others who were classified as normal weight.
Link ID: 19812 - Posted: 07.10.2014
|By Emilie Reas A poor diet can eat away at brain health. Now a study in Neurology helps elucidate why. It suggests that eating a lot of sugar or other carbohydrates can be hazardous to both brain structure and function. Diabetes, which is characterized by chronically high levels of blood glucose, has been linked to an elevated risk of dementia and a smaller hippocampus, a brain region critical for memory. The new study sought to identify whether glucose had an effect on memory even in people without the disease because having it could induce other brain changes that confound the data. In the experiment, researchers at the Charité University Medical Center in Berlin evaluated both short- and long-term glucose markers in 141 healthy, nondiabetic older adults. The participants performed a memory test and underwent imaging to assess the structure of their hippocampus. Higher levels on both glucose measures were associated with worse memory, as well as a smaller hippocampus and compromised hippocampal structure. The researchers also found that the structural changes partially accounted for the statistical link between glucose and memory. According to study co-author Agnes Flöel, a neurologist at Charité, the results “provide further evidence that glucose might directly contribute to hippocampal atrophy,” but she cautions that their data cannot establish a causal relation between sugar and brain health. These findings indicate that even in the absence of diabetes or glucose intolerance, higher blood sugar may harm the brain and disrupt memory function. Future research will need to characterize how glucose exerts these effects and whether dietary or lifestyle interventions might reverse such pathological changes. © 2014 Scientific American
Link ID: 19798 - Posted: 07.08.2014
Priyanka Pulla Not everyone who is obese is unhealthy. So say some researchers, who note that a small fraction of overweight people have normal blood sugar levels and blood pressure, and are thus “healthy obese.” Now, scientists have identified a single protein that seems to determine whether obesity is harmful or benign. The protein is a new player in our understanding of how obesity leads to disease, says Alan Saltiel, a cell biologist at the University of Michigan, Ann Arbor, who was not involved in the study. It is well known that obesity leads to a wide range of health problems, from diabetes to heart disease to cancer. So established is the link between extra pounds and illness that last year the American Medical Association voted to classify obesity itself as a disease. Although some researchers have suggested that a small number of obese people are healthy, that idea remains controversial. Instead, the emerging consensus is that healthy obesity is a transient phase, says Ravi Retnakaran, an endocrinologist at the Leadership Sinai Centre for Diabetes in Toronto, Canada. Sooner or later, he says, these outliers will develop metabolic syndrome, a condition in which glucose, cholesterol, and lipid levels soar, causing diabetes and heart disease. In fact, so-called healthy obese people may already have early signs of disease, which are too muted to show up on routine tests. In a study of more than 14,000 metabolically healthy Korean people last year, scientists found early plaque buildup in the arteries of obese subjects more often than they did in the lean ones. © 2014 American Association for the Advancement of Science
Link ID: 19797 - Posted: 07.04.2014
By LISA SANDERS, M.D. On Wednesday, we challenged Well readers to solve the case of a middle-aged woman who suddenly began to have episodes of confusion caused by low blood sugars. Her endocrinologist thought she might have an insulinoma, an insulin-producing tumor of the pancreas, but the testing he did seemed to rule out that diagnosis. Nearly 200 of you took on the challenge of trying to figure out what was causing her life-threatening drops in blood sugar level. The correct diagnosis is… Insulinoma The first respondent to make the diagnosis was Karen Unkel of Kinder, La. She is not a doctor but has a longstanding interest in hypoglycemia that allowed her to recognize the disease even in the face of an apparently negative work-up. Well done, Ms. Unkel. An insulinoma is a rare tumor of pancreatic tissue that makes and secretes insulin independently of blood glucose levels. This results in episodes of hypoglycemia that can be quite severe, even life-threatening. The diagnosis is suspected when a patient fulfills what is known as Whipple’s triad: 1) symptoms of hypoglycemia 2) associated with low measured blood sugar and 3) which improve when blood sugar is raised to the normal range. The diagnosis is made when doctors show that the patient is making too much insulin given his or her blood sugar level. Measuring insulin levels is not always accurate because insulin is processed rapidly in the body and because it is difficult to distinguish between insulin made naturally in the pancreas and any insulin that the patient might be injecting. What is measured instead is something known as C-peptide. Insulin is first made as a larger molecule known as proinsulin. When blood sugar rises, an extra bit is shaved off the molecule; that extra bit is C-peptide, and both the resulting insulin and C-peptide are released into the bloodstream. © 2014 The New York Times Company
By ANDREW POLLACK It is a tantalizingly simple idea for losing weight: Before meals, swallow a capsule that temporarily swells up in the stomach, making you feel full. Now, some early results for such a pill are in. And they are only partly fulfilling. People who took the capsule lost 6.1 percent of their weight after 12 weeks, compared with 4.1 percent for those taking a placebo, according to results presented Sunday at an endocrinology meeting in Chicago. Gelesis, the company developing the capsule, declared the results a triumph and said it would start a larger study next year aimed at winning approval for the product, called Gelesis100. “I’m definitely impressed, absolutely,” Dr. Arne V. Astrup, head of the department of nutrition, exercise and sports at the University of Copenhagen in Denmark and the lead investigator in the study, said in an interview. He said the physical mode of action could make the product safer than many existing diet drugs, which act chemically on the brain to influence appetite. But Dr. Daniel H. Bessesen, an endocrinologist at the University of Colorado who was not involved in the study, said weight loss of 2 percent beyond that provided by a placebo was “very modest.” “It doesn’t look like a game changer,” he said. Gelesis, a privately held company based in Boston, is one of many trying to come up with a product that can provide significant weight loss without bariatric surgery. Two new drugs — Qsymia from Vivus, and Belviq from Arena Pharmaceuticals and Eisai — have had disappointing sales since their approvals in 2012. Reasons include modest effectiveness, safety concerns, lack of insurance reimbursement and a belief among some doctors and overweight people that obesity is not a disease. © 2014 The New York Times Company
Link ID: 19758 - Posted: 06.23.2014
Jennifer Couzin-Frankel What if you could trick your body into thinking you were racing on a treadmill—and burning off calories at a rapid clip—while simply walking down the street? Changing our rate of energy expenditure is still far into the future, but work in mice explores how this might happen. Two teams of scientists suggest that activating immune cells in fat can convert the tissue from a type of fat that stores energy to one that burns it, opening up potential new therapies for obesity and diabetes. There are two types of fat in humans: white adipose tissue, which makes up nearly all the fat in adults, and brown adipose tissue, which is found in babies but disappears as they age. Brown fat protects against the cold (it’s also common in animals that hibernate), and researchers have found that mice exposed to cold show a temporary “browning” of some of their white fat. The same effect occurred in preliminary studies of people, where the browning—which creates a tissue known as beige fat—helps generate heat and burn calories. But cold is “the only stimulus we know that can increase beige fat mass or brown fat mass,” says Ajay Chawla, a physiologist at the University of California (UC), San Francisco. He wanted to better understand how cold caused this change in the tissue and whether there was a way to mimic cold and induce browning some other way. A few years ago, Chawla’s group had reported that cold exposure activated macrophages, a type of immune cell, in white adipose tissue. To further untangle what was going on, Chawla, his postdoc Yifu Qiu, and their colleagues used mice that lacked interleukin-4 (IL-4) and interleukin-13, proteins that help activate macrophages. When they exposed these mice to the cold, the animals developed far fewer beige fat cells than did normal animals, suggesting that macrophages were key to browning of white fat. © 2014 American Association for the Advancement of Science
Link ID: 19732 - Posted: 06.14.2014
by Lauren Hitchings Being cold can burn calories but no one wants to freeze just to sculpt their muffin-top. Soon we may not have to. Researchers have identified immune molecules triggered by cold temperatures that make obese mice lose weight – without the need for the mercury to drop. Humans and other mammals respond to cold in two ways. On the surface, we shiver to burn energy and produce a quick burst of heat. On a deeper level, as Ajay Chawla at the University of California, San Francisco, and his colleagues recently discovered, cold temperatures send signals to immune molecules called macrophages. They, in turn, release other molecules that convert energy-storing white fat into another type that burns energy. Babies and some hibernating animals have lots of these energy-burning cells – known as brown fat – but it almost all disappears as people age. We now know that cold temperatures can trigger a "browning" of white fat in adults – converting some of their white fat into an intermediate form called beige fat. It may seem counterintuitive for our bodies to use up fat stores when we get cold, but think of the white fat as the wooden walls of a log cabin – having them there is a good way to keep warm generally, but when the cold sets in, you're going to want firewood – brown or beige fat, to burn. Now Chawla's team have identified interleukin-4 and interleukin-13 as the signalling molecules that kick-start the transition of white fat to its darker counterpart. What's more, by injecting mice with interleukin-4 four times over a period of eight days, the team was able to bypass the physical cold stimulus and activate the pathway biochemically. © Copyright Reed Business Information Ltd.
Link ID: 19719 - Posted: 06.10.2014