Archive for the ‘Weight loss’ Category

Researchers at The University of Auckland have shown for the first time that the mere presence of carbohydrate solution in the mouth immediately boosts muscle strength, even before it is swallowed.

The results suggest that a previously unknown neural pathway is activated when receptors in the mouth detect carbohydrate, stimulating parts of the brain that control muscle activity and producing an increase in muscle strength.

Previous research had shown that the presence of carbohydrate in the mouth can improve physical performance during prolonged activity, but the mechanism involved was not known and it was unclear whether a person must be fatigued for the effect to be seen.

“There appears to be a pathway in the brain that tells our muscles when energy is on the way,” says lead researcher Dr Nicholas Gant from the Department of Sport and Exercise Science.

“We have shown that carbohydrate in the mouth produces an immediate increase in neural drive to both fresh and fatigued muscle and that the size of the effect is unrelated to the amount of glucose in the blood or the extent of fatigue.”

The current research has been published in the journal Brain Research and has also captured the attention of New Scientist magazine.

In the first of two experiments, 16 healthy young men who had been doing biceps exercises for 11 minutes were given a carbohydrate solution to drink or an identically flavored energy-free placebo. Their biceps strength was measured before and immediately afterward, as was the activity of the brain pathway known to supply the biceps.

Around one second after swallowing the drink, neural activity increased by 30 percent and muscle strength two percent, with the effect lasting for around three minutes. The response was not related to the amount of glucose in the bloodstream or how fatigued the participants were.

“It might not sound like much, but a two percent increase in muscle strength is enormous, especially at the elite level. It’s the difference between winning an Olympic medal or not,” says co-author Dr Cathy Stinear.

As might be expected, a second boost in muscle strength was observed after 10 minutes when carbohydrate reached the bloodstream and muscles through digestion, but no additional boost in neural activity was seen at that time.

“Two quite distinct mechanisms are involved,” says Dr Stinear. “The first is the signal from the mouth via the brain that energy is about to be available and the second is when the carbohydrate actually reaches the muscles and provides that energy,” says Dr Stinear.

“The carbohydrate and placebo solutions used in the experiment were of identical flavor and sweetness, confirming that receptors in the mouth can process other sensory information aside from the basic taste qualities of food. The results suggest that detecting energy may be a sixth taste sense in humans,” says Dr Gant.

In the second experiment, 17 participants who had not been doing exercise and were not fatigued simply held one of the solutions in their mouths without swallowing. Measurements of the muscle between the thumb and index finger were taken while the muscle was either relaxed or active.

A similar, though smaller effect was observed as in the first experiment, with a nine percent increase in neural activity produced by the carbohydrate solution compared with placebo. This showed that the response is seen in both large powerful muscles and in smaller muscles responsible for fine hand movements.

“Together the results show that carbohydrate in the mouth activates the neural pathway whether or not muscles are fatigued. We were surprised by this, because we had expected that the response would be part of the brain’s sophisticated system for monitoring energy levels during exercise,” says Dr Stinear.

“Seeing the same effect in fresh muscle suggests that it’s more of a simple reflex – part of our basic wiring – and it appears that very ancient parts of the brain such as the brainstem are involved. Reflexive movements in response to touch, vision and hearing are well known but this is the first time that a reflex linking taste and muscle activity has been described,” she says.

Further research is required to determine the precise mechanisms involved and to learn more about the size of the effect on fresh versus fatigued muscle.

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Article adapted by MD Sports from original press release.
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Contact: Pauline Curtis
The University of Auckland

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Women who walked two or more hours a week or who usually walked at a brisk pace (3 miles per hour or faster) had a significantly lower risk of stroke than women who didn’t walk, according to a large, long-term study reported in Stroke: Journal of the American Heart Association.

The risks were lower for total stroke, clot-related (ischemic) stroke and bleeding (hemorrhagic) stroke, researchers said.

Compared to women who didn’t walk:

  • Women who usually walked at a brisk pace had a 37 percent lower risk of any type of stroke and those who walked two or more hours a week had a 30 percent lower risk of any type of stroke.
  • Women who typically walked at a brisk pace had a 68 percent lower risk of hemorrhagic stroke and those who walked two or more hours a week had a 57 percent lower risk of hemorrhagic stroke.
  • Women who usually walked at a brisk pace had a 25 percent lower risk of ischemic stroke and those who usually walked more than two hours a week had a 21 percent lower risk of ischemic stroke — both “borderline significant,” according to researchers.

“Physical activity, including regular walking, is an important modifiable behavior for stroke prevention,” said Jacob R. Sattelmair, M.Sc., lead author and doctoral candidate in epidemiology at Harvard School of Public Health in Boston, Mass. “Physical activity is essential to promoting cardiovascular health and reducing risk of cardiovascular disease, and walking is one way of achieving physical activity.”

More physically active people generally have a lower risk of stroke than the least active, with more-active persons having a 25 percent to 30 percent lower risk for all strokes, according to previous studies.

“Though the exact relationship among different types of physical activity and different stroke
subtypes remains unclear, the results of this specific study indicate that walking, in particular, is associated with lower risk of stroke,” Sattelmair said.

Researchers followed 39,315 U.S. female health professionals (average age 54, predominantly white) participating in the Women’s Health Study. Every two to three years, participants reported their leisure-time physical activity during the past year — specifically time spent walking or hiking, jogging, running, biking, doing aerobic exercise/aerobic dance, using exercise machines, playing tennis/squash/racquetball, swimming, doing yoga and stretching/toning. No household, occupational activity or sedentary behaviors were assessed.

They also reported their usual walking pace as no walking, casual (about 2 mph), normal (2.9 mph), brisk (3.9 mph) or very brisk (4 mph).

Sattelmair noted that walking pace can be assessed objectively or in terms of the level of exertion, using a heart rate monitor, self-perceived exertion, “or a crude estimate such as the ‘talk test’ – wherein, for a brisk pace, you should be able to talk but not able to sing. If you cannot talk, slow down a bit. If you can sing, walk a bit faster.”

During 11.9 years of follow-up, 579 women had a stroke (473 were ischemic, 102 were hemorrhagic and four were of unknown type).

The women who were most active in their leisure time activities were 17 percent less likely to have any type of stroke compared to the least-active women.

Researchers didn’t find a link between vigorous activity and reduced stroke risk. The reason is unclear, but they suspect that too few women reported vigorous activity in the study to get an accurate picture and/or that moderate-intensity activity may be more effective at lowering blood pressure as suggested by some previous research.

Stroke is the third leading cause of death and a leading cause of serious disability in the United States, so it’s important to identify modifiable risk factors for primary prevention, Sattelmair said.

An inverse association between physical activity and stroke risk is consistent across genders. But there tend to be differences between men and women regarding stroke risk and physical activity patterns.

“The exact relation between walking and stroke risk identified in this study is not directly generalizable to men,” Sattelmair said. “In previous studies, the relation between walking and stroke risk among men has been inconsistent.”

The study is limited because it was observational and physical activity was self-reported. But strengths are that it was large and long-term with detailed information on physical activity, he said.

Further study is needed on more hemorrhagic strokes and with more ethnically diverse women, Sattelmair said.

The American Heart Association recommends for substantial health benefits, adults should do at least 150 minutes a week of moderate-intensity or 75 minutes a week of vigorous-intensity aerobic physical activity or a combination.

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Article adapted by MD Sports from original press release.
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Contact: Birdgette McNeill
American Heart Association

Molecular switch found in mice could lead to future obesity treatments, scientists say

A surprise discovery — that calorie-burning brown fat can be produced experimentally from muscle precursor cells in mice — raises the prospect of new ways to fight obesity and overweight, say scientists from Dana-Farber Cancer Institute.

Reporting in the Aug. 21 issue of the journal Nature, the researchers demonstrated that brown fat, which is known as the “good” form of fat — so called because it burns calories and releases energy, unlike “bad” white fat that simply stores extra calories — can be generated from unspecialized precursors that routinely spawn skeletal muscle.

The team led by Dana-Farber’s Bruce Spiegelman, PhD, showed that a previously known molecular switch, PRDM16, regulates the creation of brown fat from immature muscle cells. They also determined that the process is a two-way street: Knocking out PRDM16 in brown fat cells can convert them into muscle cells. However, Spiegelman called the latter an “experimental lab trick” for which he currently envisions no practical applications.

The “huge surprise” of the study results, he said, was that muscle precursor cells known as “satellite cells” are able to give birth to brown fat cells under the control of PRDM16.

Spiegelman said the finding confirms that PRDM16 is the “master regulator” of brown fat development. The confirmation will spur ongoing research in his laboratory, he said, to see if drugs that rev up PRDM16 in mice — and potentially, in people — could convert white fat into brown fat and thereby treat obesity. Another strategy, he said, might be to transplant brown fat cells into an overweight person to turn on the calorie-burning process.

“I think we now have very convincing evidence that PRDM16 can turn cells into brown fat cells, with the possibility of combating obesity,” said Spiegelman, the senior author of the paper. The lead author is Patrick Seale, PhD, a postdoctoral fellow in the Spiegelman lab.

Another paper in the same issue of Nature described a different trigger of brown fat production, a molecule called BMP7. A commentary in the journal by Barbara Cannon, an internationally recognized researcher in the biology of fat cells at the University of Stockholm, said that the two reports “take us a step closer to the ultimate goal of promoting the brown fat lineage as a potential way of counteracting obesity.”

The Spiegelman group has long studied fat cells both as a model for normal and abnormal cell development, which relates to cancer, and also because fat cells play such a key role in the growing epidemics of obesity and diabetes.

There is much interest in brown fat’s role in regulating metabolism. Rodents and human infants have abundant brown fat that dissipates food energy as heat to protect against the cold. Though human adults have little brown fat, it apparently does have a metabolic function, including the potential to be amplified in some way to combat obesity.

In 2007, Spiegelman and colleagues reported they had inserted PRDM16 genes into white fat precursors, which they implanted under the skin of mice. The PRDM16 switch coaxed the white fat precursors to produce brown fat cells instead of white. To Spiegelman, this suggested the possibility of transplanting PRDM16-equipped white fat precursors into people who are at high risk of becoming obese, to shift their metabolism slightly into a calorie-burning mode.

The new research adds another potential source of brown fat — the muscle cell progenitors, or myoblasts, that exist in the body to replace mature muscle cells as needed. The progenitors, which can be thought of as “adult stem cells,” are committed to becoming specialized muscle cells when activated by appropriate signals, or, as the study revealed, brown fat cells when PDRM16 is turned on. The PRDM16 trigger “is very powerful at what it does,” said Spiegelman, who is also a professor of cell biology at Harvard Medical School.

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Article adapted by MD Sports from original press release.
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Contact: Bill Schaller
Dana-Farber Cancer Institute 

Other authors of the paper include Bryan Bjork, PhD, and David R. Beier, PhD, MD, of Brigham and Women’s Hospital; Michael Rudnicki, PhD, of the Ottawa Health Research Institute; and Hediye Erdjument-Bromage, PhD, and Paul Tempst, PhD, of Memorial Sloan-Kettering Cancer Center.

Dana-Farber Cancer Institute (www.dana-farber.org) is a principal teaching affiliate of the Harvard Medical School and is among the leading cancer research and care centers in the United States. It is a founding member of the Dana-Farber/Harvard Cancer Center (DF/HCC), designated a comprehensive cancer center by the National Cancer Institute.

Researchers from the Division of Health Promotion & Sports Medicine at Oregon Health & Science University have found steroid use among teen girls is not limited to athletes and often goes hand in hand with other unhealthy choices, including smoking and taking diet pills. The study was published in the Archives of Pediatrics & Adolescent Medicine, a JAMA/Archives journal.Diane Elliot, M.D., professor of medicine (health promotion and sports medicine), OHSU School of Medicine, and colleagues analyzed findings from the Center for Disease Control’s Youth Risk Behavior Survey of 7,544 ninth- through 12th-grade girls from around the country. The questionnaire asked about sports participation, anabolic steroid and drug use, and other illegal or unhealthy behaviors. Approximately 5 percent of participants reported prior or ongoing anabolic steroid use.

In addition to greater substance use, young female steroid users were more likely to have had sexual intercourse before age 13; have been pregnant; drink and drive or have ridden with a drinking driver; carry a weapon; have been in a fight on school property; have feelings of sadness or hopelessness almost every day for at least two weeks; and have attempted suicide. Those reporting anabolic steroid use were less likely to participate in team athletics.

Overall, more than two-thirds of those surveyed reported trying to change their weight. Girls who used steroids were more likely try extreme weight-loss techniques, such as vomiting and laxative use.

Adolescent girls reporting anabolic steroid use had significantly more other health-harming behaviors, Elliot explained, “They were much more likely to use other unhealthy substances, including cigarettes, alcohol, marijuana and cocaine.”

“Across all grades, these seem to be troubled adolescents with co-occurring health-compromising activities in the domains of substance use, sexual behavior, violence and mental health,” Elliot said. “Anabolic steroid use is a marker for high-risk girls. High-risk young women have received less attention than young men, perhaps reflecting that their actions are less socially, albeit more personally, destructive. Further study is needed to develop effective interventions for these young women.”

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Article adapted by MD Sports Weblog from original press release.
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Contact: Tamara Hargens
Oregon Health & Science University

New research on the effects of the female sex hormone estrogen in the brain lend credence to what many women have suspected about the hormonal changes that accompany aging: Menopause can make you fat.Scientists long have sought to understand how changes in hormones during menopause could account for the increase in appetite and accompanying weight gain that often occurs among aging women.

In a series of animal experiments described today at the 234th national meeting of the American Chemical Society, the world’s largest scientific society, researchers showed how estrogen receptors located in the hypothalamus serve as a master switch to control food intake, energy expenditure and body fat distribution. When these receptors are destroyed, the animals immediately begin to eat more food, burn less energy and pack on pounds.

This research seems to support a link between estrogen and regulation of obesity, especially the dangerous accumulation of abdominal fat linked to heart disease, diabetes, and cancer, says Deborah J. Clegg, Ph. D., assistant professor of psychiatry at the University of Cincinnati Academic Health Center, who is directing the studies.

The findings may also help scientists develop more targeted hormone replacement therapies, capable of stimulating estrogen receptors in one part of the brain or body while dampening it in the next, Clegg says.

Estrogen receptors are located on cells throughout a woman’s body. Previous studies have shown that one type of estrogen receptor, known as estrogen receptor alpha or ER-alpha, plays a role in regulating food intake and energy expenditure. But scientists have been unable to pinpoint exactly where these fat-regulating receptors reside or how they work to govern these behaviors.

To determine the effect of dwindling estrogen levels in the brain, Clegg and her colleagues are focusing on two ER-alpha rich regions located in the hypothalamus, an area of the brain that controls body temperature, hunger and thirst. The first region, called the ventromedial nucleus or VMN, is a key center for energy regulation.

Using a relatively new gene-silencing technique called RNA interference, the researchers in earlier research deactivated the alpha-receptors in the VMN. The estrogen receptors in other regions of the brain maintained their normal capacity.

When estrogen levels in the VMN dipped, the animals’ metabolic rate and energy levels also plummeted. The findings show the animals quickly developed an impaired tolerance to glucose and a sizable weight gain, even when their caloric intake remained the same. What’s more, the excess weight went straight to their middle sections, creating an increase in visceral fat.

The findings suggested that the ER-alpha in this region plays an essential role in controlling energy balance, body fat distribution and normal body weight.

Clegg now plans to perform a similar experiment to deactivate ER-alpha in the arcuate nucleus region of the hypothalamus. This region contains two populations of neurons: one puts the brake on food intake and the other stimulates food intake. Clegg anticipates that a loss of estrogen in this region may create an increase in the animals’ appetites as well as their weight.

Clegg says her studies address an area that is sorely needed given the incidence and impact of gender differences in obesity and its complications.

“The accumulation of abdominal fat puts both men and women at a heightened risk of cardiovascular disease, diabetes, and insulin resistance,” she says. “Women are protected from these negative consequences as long as they carry their weight in their hips and saddlebags. But when they go through menopause and the body fat shifts to the abdomen, they have to start battling all of these medical complications.”

By identifying the critical brain regions that determine where body fat is distributed, Clegg says her findings may help scientists design hormone replacement therapies to better manage and manipulate estrogen levels.

“If we could target those critical regions and estrogen receptors associated with weight gain and energy expenditure, we could perhaps design therapies that help women sidestep many of the complications brought on by the onset of menopause,” she says.

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Article adapted by MD Sports Weblog from original press release.
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Contact: Charmayne Marsh
American Chemical Society

 The American Chemical Society — the world’s largest scientific society — is a nonprofit organization chartered by the U.S. Congress and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.

Deborah J. Clegg, Ph.D., is assistant professor of psychiatry at the University of Cincinnati Academic Health Center in Cincinnati, Ohio.

The old adage “use it or lose it” is truer than ever. People who maintain a vigorously active lifestyle as they age gain less weight than people who exercise at more moderate levels, according to a first-of-its-kind study that tracked a large group of runners who kept the same exercise regimen as they grew older. The study also found that maintaining exercise with age is particularly effective in preventing extreme weight gain, which is associated with high blood pressure, high cholesterol, diabetes, and other diseases.

The study, conducted by Paul Williams of the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), followed 6,119 men and 2,221 women who maintained their weekly running mileage (to within three miles per week) over a seven-year period. On average, the men and women who ran over 30 miles per week gained half the weight of those who ran less than 15 miles per week.

“To my knowledge, this is the only study of its type,” says Williams, a staff scientist in Berkeley Lab’s Life Sciences Division. “Other studies have tracked exercise over time, but the majority of people will have changed their exercise habits considerably.”

The research is the latest report from the National Runners’ Health Study, a 20-year research initiative started by Williams that includes more than 120,000 runners. It appears in the May issue of the journal Medicine and Science in Sports and Exercise.

Specifically, between the time subjects entered the study and when they were re-contacted seven years later, 25-to-34-year-old men gained 1.4 pounds annually if they ran less than 15 miles per week. In addition, male runners gained 0.8 pounds annually if they ran between 15 and 30 miles per week, and 0.6 pounds annually if they ran more than 30 miles per week.

This trend is mirrored in women. Women between the ages of 18 and 25 gained about two pounds annually if they ran less than 15 miles per week, 1.4 pounds annually if they ran 15 to 30 miles per week, and slightly more than three-quarters of a pound annually if they ran more than 30 miles per week. Other benefits to running more miles each week included fewer inches gained around the waist in both men and women, and fewer added inches to the hips in women.

“As these runners aged, the benefits of exercise were not in the changes they saw in their bodies, but how they didn’t change like the people around them,” says Williams.

Although growing older and gaining weight is something of a package deal, it isn’t the same in everyone. The lucky few remain lean as they age, most people pack on several pounds, and some people become obese. The latter group is particularly at risk for high blood pressure, high cholesterol, and diabetes. Fortunately, Williams’ results show that maintaining exercise can combat such extreme weight gain.

“Getting people to commit to a vigorously active lifestyle while young and lean will go a long way to reducing the obesity epidemic in this country,” says Williams.

Another paper published in the November 2006 issue of the journal Obesity by Williams and Paul Thompson of Hartford (CT) Hospital found that runners who increased their running mileage gained less weight than those who remained sedentary, and runners that quit running became fatter.

“The time to think about exercise is before you think you need it,” says Williams. “The medical journals are full of reports on how difficult it is to regain the slenderness of youth. The trick is not to get fat.”

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Article adapted by MD Sports Weblog from original press release.
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Contact: Dan Krotz
DOE/Lawrence Berkeley National Laboratory

Williams’ research was funded by the National Heart, Lung and Blood Institute. The study in the May issue of the journal Medicine and Science in Sports and Exercise is entitled Maintaining Vigorous Activity Attenuates 7-yr Weight Gain in 8,340 Runners.

Taking a break in the middle of your workout may metabolize more fat than exercising without stopping, according to a recent study in Japan. Researchers conducted the first known study to compare these two exercise methods—exercising continually in one long bout versus breaking up the same workout with a rest period. The findings could change the way we approach exercise. Who wouldn’t want to take a breather for that”“Many people believe prolonged exercise will be optimal in order to reduce body fat, but our study has shown that repetitions of shorter exercise may cause enhancements of fat mobilization and utilization during and after the exercise. These findings will be informative about the design of [future] exercise regimens,” said lead researcher Kazushige Goto, Ph.D. “Most people are reluctant to perform a single bout of prolonged exercise. The repeated exercise with shorter bouts of exercise will be a great help [in keeping up with fitness].”

This finding is part of a study entitled Enhancement of fat metabolism by repeated bouts of moderate endurance exercise, found in the June 2007 edition of the Journal of Applied Physiology, which is published by the American Physiological Society. It was conducted by Kazushige Goto, of both the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo, Japan and the Institute of Sports Medicine, Bispebjerg Hospital, Copenhagen, Denmark; Naokata Ishii, of the Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Tokyo, Japan; and Ayuko Mizuno and Kaoru Takamatsu, both of the Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.

Summary of Methodology

The researchers used seven healthy (avg. body mass: 66.1, percentage fat: 17.6) men with an average age of 25 who were physically active and familiar with exercise and had them perform three separate trials:

  • one single bout of 60-min exercise followed with a 60-min recovery period (Single)
  • two bouts of 30-min exercise with a 20-min rest after the first 30-min bout, along with a 60-min recovery period at the end (Repeated)
  • one 60-min rest period (Control)

The men performed each trial at the same time of day after fasting overnight. They exercised on a single ergometer (cycling machine) at the commonly recommended exercise prescription of 60% maximum oxygen intake. The recovery and rest periods were conducted while the subjects sat in chairs. Blood samples were taken every 15 minutes during the exercise and every 30 minutes during the recovery period. Their respiratory gas and heart rates were monitored continuously throughout the trial.

Summary of Results

The Repeated trial showed a greater amount of lipolysis (fat breakdown) than did the Single trial. This Repeated trial also had a pronounced increase in free fatty acids and glycerol (chemical compounds that are released when stored fat is used) concentrations in the final 15 minutes of exercise, whereas these concentrations only progressively increased throughout the Single trial. Also, the second half of the Repeated trial showed a significantly greater epinephrine response while also having a rapid decrease in insulin concentration as a result of lower plasma glucose. This combination of high epinephrine and low insulin concentration may have also increased the lipolysis. There was also enhanced fat oxidation in the recovery period of the Repeated trial than in the Single trial, but this result may be because the free fatty acids concentration was already high before the recovery period.

Conclusions

The American College of Sports Medicine recommends moderate exercise for the duration of 45 to 60 minutes to ensure a sufficient amount of energy is depleted in obese individuals. This has caused a greater focus on extending exercise sessions in order to burn more fat. However, this study shows that this method may not be the most effective way to enhance fat metabolism, as splitting up a long bout of exercise with a rest period burns more fat than a continuous bout of exercise. This study could help with the practical application of implementing new exercise methods in order to better manage and control weight in individuals in the future. However, Goto and his team of researchers plan on conducting further studies in order to explore the results in a variety of exercise durations as well as in different types of individuals.

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Article adapted by MD Only Weblog from original press release.
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Contact: Celia Lee
American Physiological Society