Category: Diet and Weight Loss

 The brains of mice fed a high-fat diet for an extended period of time showed irreversible changes in areas associated with reward and pleasure, a new study has found.

The research was presented at Neuroscience 2010, the annual meeting of the Society for Neuroscience, held in San Diego.

"Our data show that chronic consumption of a high-fat diet leads to significant changes in brain chemistry," said senior author Teresa Reyes, PhD, of the University of Pennsylvania, School of Medicine.

Fatty foods tap the pleasure centers of the brain, the same areas triggered by cocaine or heroin. Reyes and her colleagues explored whether these pathways could be modified on a molecular level by eating a high-fat diet for a long period of time. The researchers found that the genes involved with reward were altered in mice fed a high-fat diet for more than six months. The authors suggest the changes, which may promote cravings for fatty foods, could have far-reaching consequences.

Many people struggle with unhealthy cycles of weight loss and gain. This study illustrates the biological challenges of breaking out of this cycle. "These results provide further insight into the health consequences of long-term, high-fat diets, and suggest one explanation for why some people face such difficulty in the path to weight loss and healthier eating," Reyes said.

Research was supported by the National Institute of Mental Health.

Regular exercise can reduce around two dozen physical and mental health conditions and slow down how quickly the body ages, according to a research review summarising the key findings of 40 papers published between 2006 and 2010.

The paper provides an invaluable source for both news and feature editors as it is divided into a number of key sections, ranging from: "Why should I exercise" to "I'm too busy, I don't have time." Health conditions covered by the review include: cancer, heart disease, dementia, stroke, type 2 diabetes, depression, obesity and high blood pressure.

People who take regular exercise could reduce their risk of developing around two dozen physical and mental health conditions — including some cancers and dementia — and slow down how quickly their body deteriorates as they age.

An extensive research review, published in the December issue of IJCP, the International Journal of Clinical Practice, says that apart from not smoking, being physically active is the most powerful lifestyle choice any individual can make to improve their health.

Physiotherapist and lecturer Leslie Alford from the University of East Anglia reviewed 40 papers covering the latest international research published between 2006 and 2010.

"The literature reviewed shows that how long people live and how healthy they are depends on a complex mix of factors, including their lifestyle, where they live and even luck" says Mr Alford. "Individuals have an element of control over some of these factors, including obesity, diet, smoking and physical activity.

"Although the focus of my study was on men's health, the messages on physical activity are relevant to both sexes and all age groups."

Health benefits identified by the review include:

• Regular moderate to intense physical activity is associated with decreased risk of coronary heart disease and ischaemic and haemorrhagic stroke.
• A growing body of evidence suggests that increasing physical activity can also reduce the risk of certain types of cancers, osteoporosis, type 2 diabetes, depression, obesity and high blood pressure.
• Evidence of the beneficial effects of physical activity in the primary prevention and management of cancer is growing and there is an association between higher levels of physical activity and lower cancer death rates.
• Research has found that walking or cycling for at least an half-an-hour a day is associated with a reduction in cancer and that when this is increased to an hour cancer incidence falls by 16 per cent.
• Evidence is mixed when it comes to specific cancers. Research has shown a strong relationship between increased physical activity and reduced colon cancer in both sexes. And men who are more active at work — not just sitting at a desk — have lower rates of prostate cancer.
• Other cancer studies show that physical activity after diagnosis can aid recovery and improve outcomes.
• Studies have also shown that men who are physically active are less likely to experience erection problems.
• There is growing evidence that physical activity could decrease the risk of dementia in the elderly.

Recommendations identified by the review include:

• Healthy adults aged between 18 and 65 should aim for 150 minutes of moderate intensity physical activity a week, such as 30 minutes of brisk walking, five days a week. And people who undertake more vigorous intensity exercise, such as jogging, should aim for 20 minutes three days a week.
• Healthy adults should aim for two strength-training sessions a week that work with the body's major muscle groups.
• Older people can benefit from exercise that helps to maintain their balance and flexibility.
• People who are physically active should continue to exercise even when they become middle aged or elderly and those who aren't should increase their physical activity.
• Not smoking and following a healthy diet is also important.

"Ideally, to gain maximum health benefits people should exercise, not smoke, eat a healthy diet and have a body mass index of less than 25" says Mr Alford. "The more of these healthy traits an individual has, the less likely they are to develop a range of chronic disorders. Even if people can't give up smoking and maintain a healthy weight, they can still gain health benefits from increasing the amount of regular exercise they take.

"Physical inactivity results in widespread pathophysiological changes to our bodies. It appears that our bodies have evolved to function optimally on a certain level of physically activity that many of us simply do not achieve in our modern, sedentary lifestyles.

"What is clear from the research is that men and women of all ages should be encouraged to be more physically active for the sake of their long-term health."

Journal Reference:

1. L. Alford. What men should know about the impact of physical activity on their health. International Journal of Clinical Practice, 2010; 64 (13): 1731 DOI: 10.1111/j.1742-1241.2010.02478.x

High cholesterol levels in middle age do not appear to increase women's risk of developing Alzheimer's disease and other forms of dementia later in life, new Johns Hopkins-led research finds, despite a body of scientific evidence long suggesting a link between the two.

What the study, published online in the journal Neurology, does find is that women whose cholesterol levels decline from middle age to old age are at 2.5 times greater risk of developing the memory-wasting diseases than those whose cholesterol stayed the same or increased over the years.

"Our research refutes the notion that high cholesterol in midlife is a risk factor for Alzheimer's disease, at least among women," says Michelle M. Mielke, Ph.D., an assistant professor of psychiatry at the Johns Hopkins University School of Medicine and the study's lead author.

Even though Mielke and her colleagues found no link between high middle-age cholesterol levels and dementia risk, Mielke cautions that people still need to watch their cholesterol. High cholesterol levels are linked to cardiovascular and other diseases. Cholesterol levels can be kept in check through diet, exercise and medication.

Mielke and her colleagues examined data from the Prospective Population Study of Women, which began in 1968 and consisted of 1,462 Swedish women ages 38 to 60. Follow-ups were conducted at four intervals across the intervening decades, with the most recent examinations concluding in 2001. As part of the study, the women were given physical exams, heart tests, chest x-rays and blood tests. The group was also surveyed for smoking habits, alcohol and medication use, education and medical history. Throughout the study, body mass index (BMI), a measurement of weight-per-height, and blood pressure were taken. Women were assessed for dementia throughout the 32 years of follow-up between 1968 and 2001. In 2001, 161 of the original group had been diagnosed with Alzheimer's or other forms of dementia, but the youngest group was just reaching age 70.

Despite the advances being made in biomarker and other dementia research, the biggest known risk factor for these neurodegenerative diseases is old age.

Mielke says that later in life, women with slightly higher body mass index, higher levels of cholesterol and higher blood pressure tend to be healthier overall than those whose weight, cholesterol and blood pressure are too low. But it is unclear whether "too low" cholesterol, BMI and blood pressure are risk factors for dementia or if they could be signs that dementia is developing, she says. For example, an inadvertent loss of weight often precedes the development of dementia, she says, but the exact cause is unclear.

The study was supported by the National Institute of Health, the National Institute on Aging, the National Institutes of Neurological Disorders and Stroke, the Swedish Research Council, the Swedish Brain Power Project, the University of Gothenburg, Swedish Council for Working Life and Social Research, Swedish Alzheimer Association, European Commission Seventh Framework Program, Svenssons Foundation, the Swedish Society of Medicine, the Söderström-Königska Nursing Home Foundation, the Foundation för Gamla Tjänarinnor, Hjalmar Svenssons Foundation, the Swedish Society of Medicine, the Göteborg Medical Society, the Lions Foundation, the Dr. Felix Neubergh Foundation, the Wilhelm and Martina Lundgren Foundation, the Elsa and Eivind Kison Sylvan Foundation, and the Alzheimer's Association Zenith Award.

Johns Hopkins associate professor Peter P. Zandi, Ph.D., also participated in the study as well as researchers from SUNY-Downstate Medical Center in Brooklyn, N.Y., and the University of Gothenburg in Sweden.

Journal Reference:

1. M.M. Mielke, P.P. Zandi, H. Shao, M. Waern, S. Östling, X. Guo, C. Björkelund, L. Lissner, I. Skoog, D.R. Gustafson. The 32-year relationship between cholesterol and dementia from midlife to late life. Neurology, 2010; DOI: 10.1212/WNL.0b013e3181feb2bf

When it comes to understanding where tendencies to overweight and obesity develop, you have to begin with the very young, says John Spence, a behavioural scientist in the Faculty of Physical Education and Recreation at the University of Alberta.

His research, the first of its kind to look at North American kids and published in the International Journal of Pediatric Obesity, examined four- and five-year-olds' avoidance or approach behaviours to food and their relationship with body weight.

What he's found may help to unlock the causes of obesity and what we can do to prevent a condition in Canada where, alarmingly, 26 per cent of 2- to 17-year-olds are overweight or obese.

Spence and his team recruited 1730 Canadian children into the study — an equal mix of boys and girls, and four- and five-year-olds — via immunization clinics from 2005 to 2007 when they came for their pre-school vaccinations. Kids were classified according to body weight status and parents asked to complete the UK-developed Children's Eating Behaviour Questionnaire (CEBQ), which has been used in European studies to establish the relationship between food behaviours and body weight in children.

Parents were given a list of statements relating to how their child responded to food, for example, "My child loves food," or "My child eats more when worried" and asked if or to what extent the behaviour occurred.

The results of the two-year study were in line with what Spence had anticipated. He found significant differences between the children in different weight status groups for food responsiveness, emotional over-eating, enjoyment of food, satiety responsiveness, slowness in eating, and food fussiness.

"It does appear that children, not surprisingly, who are demonstrating approach behaviours to food (eating when upset, or eating when bored, for example) are going to be more overweight whereas children who are demonstrating avoidance behaviours (such as fussy or slow eating) are more likely to be underweight. But the issue now is: how do children develop these approach or avoidance tendencies to food?" says Spence.

"This model suggests that to some extent this is influenced by the household environment where the parents may be rewarding children for certain types of behaviours. It would suggest that there is some dynamic in the household that is leading children to be more approach or avoidant in relation to food."

Spence says the results, which show clear linear relationships across the body weight groups, bode well for his follow-up research, now in progress.

"If we are seeing associations between where children live and play; if there are associations between the environment and the weight status of the child then we have to try and figure out how that environment influences that child," says Spence.

"Is it exposure to food, prevention or promotion of physical activity? Is it the way they interact with their food as shaped by their environment? This is more of a household variable than one would expect, so is the child being rewarded or punished in relation to their food and is that then related to their weight status? Is there education we can be providing to parents?

"These have potential intervention implications because if we can identify this and understand what the causes of approach and avoidance behaviours are, we can identify what we can intervene on."

Spence has begun a longitudinal study following the children from the original study who are now seven and eight-year-olds. This time researchers will probe deeper and with confidence knowing their work is grounded in a solid foundation of findings consistent with European studies that have used the CBEQ to establish these associations between food behaviours and body weight.

"Now we'll be situating (our research) in a larger framework with more variables and we'll be looking to see how some of these work together," says Spence. "We'll look to see if, in children who are more approach-oriented to food, we are seeing more food being consumed and are they consuming some of the 'bad' food."

Spence says he expects governments to step in with policies once researchers know more. "Now that we've established the associations, we need to know how to change things, and if we change things how do we implement those in policy, and affect populations."

Journal Reference:

1. John C. Spence, Valerie Carson, Linda Casey, Normand Boule. Examining behavioural susceptibility to obesity among Canadian pre-school children: The role of eating behaviours. International Journal of Pediatric Obesity, 2010; 100913044201049 DOI: 10.3109/17477166.2010.512087

NewsPsychology (Oct. 27, 2010) — Scientists have revealed that an anti-obesity drug changes the way the brain responds to appetising, high-calorie foods in obese individuals. This insight may aid the development of new anti-obesity drugs which reduce the activity in the regions of the brain stimulated by the sight of tasty foods.

Researchers at the University of Cambridge discovered that the anti-obesity drug sibutramine reduced brain responses in two regions of the brain, the hypothalamus and the amygdala, both of which are known to be important in appetite control and eating behaviour. Their findings are reported in The Journal of Neuroscience.

Professor Paul Fletcher, from the Department of Psychiatry and the Behavioural & Clinical Neuroscience Institute at the University of Cambridge and one of the paper’s authors, said: “Currently, there are few drugs that effectively help patients to lose weight. Developing new pharmaceuticals is expensive and risky. However, our findings suggest that we may be able to use brain imaging and psychological tests to make better predictions of which drugs are likely to work.”

Using functional magnetic resonance imaging (fMRI), the researchers measured brain activity while obese volunteers viewed pictures of appetising high-calorie foods — like chocolate cake — or pictures of low-calorie foods — like broccoli. The brain scanning was carried out both after two weeks of treatment with the anti-obesity drug, sibutramine, and two weeks of placebo treatment.

On placebo, it was shown that simply seeing pictures of appetising foods caused greater activation of many regions of the brain that are known to be important for reward processing. On sibutramine, however, they found that the anti-obesity drug reduced brain responses to the appetising foods in two regions of the volunteers’ brain — the hypothalamus and the amygdala. These two regions are known to be important in appetite control and eating behaviour. Additionally, people who had the greatest reduction of brain activation following drug treatment tended to eat less and to lose more weight.

Professor Ed Bullmore, from the Department of Psychiatry at the University of Cambridge and director of the GlaxoSmithKline (GSK) Clinical Unit in Cambridge (CUC), said: “Our results help us to understand more precisely how anti-obesity drugs work in the brain to change eating behaviour and hence, ultimately, to assist people in losing weight.

“The most exciting aspect of these results is that they help us to see that brain and behaviour are fundamental to understanding and treating obesity. Simply because obesity involves major changes in body weight and body composition, it is easy to imagine that it is entirely ‘a body problem’. These results remind us that the major cause of obesity in the West is over-eating, and this behaviour is regulated by reward and satiety processing circuits in the brain.”

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The above story is reprinted (with editorial adaptations by newsPsychology staff) from materials provided by University of Cambridge, via EurekAlert!, a service of AAAS.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of NewsPsychology or its staff.

Because of impairments in their insulin sensitivity, obese individuals demonstrate different brain responses than their normal-weight peers while completing a challenging cognitive task, according to new research by psychologists at The University of Texas at Austin.

The results provide further evidence that a healthy lifestyle at midlife could lead to a higher quality of life later on, especially as new drugs and treatments allow people to live longer.

"The good thing about insulin sensitivity is that it's very modifiable through diet and exercise," says psychology graduate student Mitzi Gonzales, who co-authored the paper published in the journal Obesity with Assistant Professor Andreana Haley and other colleagues.

To better understand why midlife obesity is linked to higher risk of cognitive decline and dementia in old age, the researchers had middle-aged adults between 40 and 60 years of age complete a challenging cognitive task while undergoing functional magnetic resonance imaging (fMRI).

While obese, overweight and normal-weight participants performed equally well on the task, obese individuals displayed lower functional brain response in one brain region, the inferior parietal lobe.

Obese participants also had lower insulin sensitivity than their normal weight and overweight peers, meaning that their bodies break down glucose less efficiently. Poor insulin sensitivity may ultimately lead to diabetes mellitus if the pancreas is unable to secrete enough insulin to compensate for reduced glucose use.

The study shows that impaired insulin sensitivity, which generally accompanies obesity, may serve as a mediator between midlife obesity and cognitive decline later on. Researchers chose to examine insulin sensitivity because insulin helps regulate people's metabolism and also affects cognitive functions.

The study exemplifies the aim of Haley's lab, which is to use neuroimaging in middle-aged individuals to provide early identification of risk for cognitive decline later in life.

"Generally, very few people study the middle-aged segment of the population, but that's when many chronic diseases are first identified and neurodegenerative processes are triggered," says Haley. "We found that while behavioral performance of obese middle-aged individuals may be the same — they can complete the same cognitive tasks as normal weight individuals — their brain is already doing something different to produce that outcome."

Haley and Gonzales are planning a follow up study to determine if a 12-week exercise intervention can reverse the observed differences in brain response.

Journal Reference:

1. Mitzi M. Gonzales, Takashi Tarumi, Steven C. Miles, Hirofumi Tanaka, Furqan Shah, Andreana P. Haley. Insulin Sensitivity as a Mediator of the Relationship Between BMI and Working Memory-Related Brain Activation. Obesity, 2010; DOI: 10.1038/oby.2010.183

A diet rich in the plant compound luteolin reduces age-related inflammation in the brain and related memory deficits by directly inhibiting the release of inflammatory molecules in the brain, researchers report.

Luteolin (LOOT-ee-oh-lin) is found in many plants, including carrots, peppers, celery, olive oil, peppermint, rosemary and chamomile.

The new study, which examined the effects of dietary luteolin in a mouse model of aging, appears in the Journal of Nutrition.

The researchers focused on microglial cells, specialized immune cells that reside in the brain and spinal cord. Infections stimulate microglia to produce signaling molecules, called cytokines, which spur a cascade of chemical changes in the brain. Some of these signaling molecules, the inflammatory cytokines, induce "sickness behavior": the sleepiness, loss of appetite, memory deficits and depressive behaviors that often accompany illness.

Inflammation in the brain also appears to be a key contributor to age-related memory problems, said University of Illinois animal sciences professor Rodney Johnson, who led the new study. Johnson directs the Division of Nutritional Sciences at Illinois.

"We found previously that during normal aging, microglial cells become dysregulated and begin producing excessive levels of inflammatory cytokines," he said.

"We think this contributes to cognitive aging and is a predisposing factor for the development of neurodegenerative diseases."

Johnson has spent nearly a decade studying the anti-inflammatory properties of nutrients and various bioactive plant compounds, including luteolin. Previous studies — by Johnson's lab and others — have shown that luteolin has anti-inflammatory effects in the body. This is the first study to suggest, however, that luteolin improves cognitive health by acting directly on the microglial cells to reduce their production of inflammatory cytokines in the brain.

The researchers showed that microglial cells that were exposed to a bacterial toxin produced inflammatory cytokines that could kill neurons. When the microglia were exposed to luteolin before they encountered the toxin, however, the neurons lived.

"The neurons survived because the luteolin inhibited the production of neurotoxic inflammatory mediators," Johnson said.

Exposing only the neurons to luteolin before the experiment had no effect on their survival, the researchers found.

"This demonstrated that luteolin isn't protecting the neurons directly," he said. "It's doing it by affecting the microglial cells."

The researchers next turned their attention to the effects of luteolin on the brains and behavior of adult (3- to 6-month-old) and aged (2-year-old) mice. The mice were fed a control diet or a luteolin-supplemented diet for four weeks. The researchers assessed their spatial memory and measured levels of inflammatory markers in the hippocampus, a brain region that is important to memory and spatial awareness.

Normally, aged mice have higher levels of inflammatory molecules in the hippocampus and are more impaired on memory tests than younger adult mice. Aged mice on the luteolin-supplemented diet, however, did better on the learning and memory task than their peers, and the levels of inflammatory cytokines in their brains were more like those of the younger adult mice.

"When we provided the old mice luteolin in the diet it reduced inflammation in the brain and at the same time restored working memory to what was seen in young cohorts," Johnson said.

Studies have shown that plant compounds such as luteolin can get into the brain, Johnson said. "We believe dietary luteolin accesses the brain and inhibits or reduces activation of microglial cells and the inflammatory cytokines they produce. This anti-inflammatory effect is likely the mechanism which allows their working memory to be restored to what it was at an earlier age."

"These data suggest that consuming a healthy diet has the potential to reduce age-associated inflammation in the brain, which can result in better cognitive health," he said.

The National Institutes of Health provided funding to support this research.

Journal Reference:

1. S. Jang, R. N. Dilger, R. W. Johnson. Luteolin Inhibits Microglia and Alters Hippocampal-Dependent Spatial Working Memory in Aged Mice. Journal of Nutrition, 2010; 140 (10): 1892 DOI: 10.3945/jn.110.123273

Babies whose mothers had relatively high levels of the chemical DDE in their blood were more likely to both grow rapidly during their first 6 months and to have a high body mass index (BMI) by 14 months, according to a team of scientists based in Barcelona, Spain. DDE, an endocrine disruptor, is a by-product of the pesticide DDT.

Published online October 5 ahead of print in the peer-reviewed journal Environmental Health Perspectives (EHP), the study examined data collected between 2004 and 2006 on a representative sample of 518 Spanish women in their first trimester of pregnancy. Among babies whose mothers were normal weight pre-pregnancy, those babies whose mothers had DDE levels in the top 75 percent of exposure were twice as likely to grow rapidly during their first 6 months as babies whose mothers had the lowest DDE levels. Infants in the top 50 percent of exposure were three times more likely to have high BMI scores at 14 months. The researchers did not observe an association between DDE and weight for babies of mothers who were overweight before pregnancy.

Two other human studies have shown an association between prenatal DDE exposure and obesity later in life. "However, this analysis suggests, to our knowledge for the first time, that fetal DDE exposure may promote rapid growth starting in the immediate postnatal period," report lead author and epidemiologist Michelle A. Mendez, of the Centre for Research in Environmental Epidemiology, and her colleagues. Laboratory studies have suggested that "exposure to chemicals with endocrine-disrupting properties might promote shifts in appetite regulation, but may also promote obesity through metabolic changes," says Mendez.

Only 14 percent of all the children had a BMI exceeding the 85th percentile, but rapid growers of both normal-weight and overweight mothers were five times more likely than other babies to have a high BMI at 14 months. Other studies have shown that infants who grow rapidly also tend to have higher levels of body fat. More than 40 studies have associated rapid weight gain in the first few months of life with obesity and metabolic disorders later in life, the team writes.

The team tested the mothers' blood serum for other organochlorine compounds with endocrine-disrupting properties, including polychlorinated biphenyls (PCBs), but these chemicals showed no association with early weight gain. The researchers controlled for other factors in rapid growth and high BMI, such as parents' height and weight, duration of breastfeeding, and whether the mother smoked. The team is continuing to study the children, who are now 4 years old.

"Most of the exposure to organochlorine compounds is thought to come from the diet," says Mendez. Foods including meats, fish, dairy products, and fruits and vegetables are potential sources of exposure to DDE and similar compounds. "These chemicals persist in the environment as they are highly resistant to degradation," Mendez says.

Journal Reference:

1. Michelle A. Mendez, Raquel Garcia-Esteban, M?nica Guxens, Martine Vrijheid, Manolis Kogevinas, Fernando Go?i, Silvia Fochs, Jordi Sunyer. Prenatal Organochlorine Compound Exposure, Rapid Weight Gain and Overweight in Infancy. Environmental Health Perspectives, 2010; DOI: 10.1289/ehp.1002169

Cutting back on sleep reduces the benefits of dieting, according to a study published October 5, 2010, in the Annals of Internal Medicine.

When dieters in the study got a full night's sleep, they lost the same amount of weight as when they slept less. When dieters got adequate sleep, however, more than half of the weight they lost was fat. When they cut back on their sleep, only one-fourth of their weight loss came from fat.

They also felt hungrier. When sleep was restricted, dieters produced higher levels of ghrelin, a hormone that triggers hunger and reduces energy expenditure.

"If your goal is to lose fat, skipping sleep is like poking sticks in your bicycle wheels," said study director Plamen Penev, MD, PhD, assistant professor of medicine at the University of Chicago. "Cutting back on sleep, a behavior that is ubiquitous in modern society, appears to compromise efforts to lose fat through dieting. In our study it reduced fat loss by 55 percent."

The study, performed at the University of Chicago's General Clinical Resource Center, followed 10 overweight but healthy volunteers aged 35 to 49 with a body mass index ranging from 25, considered overweight, to 32, considered obese. Participants were placed on an individualized, balanced diet, with calories restricted to 90 percent of what each person needed to maintain his or her weight without exercise.

Each participant was studied twice: once for 14 days in the laboratory with an 8.5-hour period set aside for sleep, and once for 14 days with only 5.5 hours for sleep. They spent their waking hours engaged in home- or office-like work or leisure activities.

During the two-week, 8.5-hours-in-bed phase, volunteers slept an average of 7 hours and 25 minutes each night. In the 5.5-hour phase, they slept 5 hours and 14 minutes, or more than two hours less. The number of calories they consumed, about 1,450 per day, was kept the same.

The volunteers lost an average of 6.6 pounds during each 14-day session. During weeks with adequate sleep, they lost 3.1 pounds of fat and 3.3 pounds of fat-free body mass, mostly protein. During the short-sleep weeks, participants lost an average of 1.3 pounds of fat and 5.3 pounds of fat-free mass.

Getting adequate sleep also helped control the dieters' hunger. Average levels of ghrelin did not change when dieters spent 8.5 hours in bed. When they spent 5.5 hours in bed, their ghrelin levels rose over two weeks from 75 ng/L to 84 ng/L.

Higher ghrelin levels have been shown to "reduce energy expenditure, stimulate hunger and food intake, promote retention of fat, and increase hepatic glucose production to support the availability of fuel to glucose dependent tissues," the authors note. "In our experiment, sleep restriction was accompanied by a similar pattern of increased hunger and … reduced oxidation of fat."

The tightly controlled circumstances of this study may actually have masked some of sleep's benefits for dieters, suggested Penev. Study subjects did not have access to extra calories. This may have helped dieters to "stick with their lower-calorie meal plans despite increased hunger in the presence of sleep restriction," he said.

The message for people trying to lose weight is clear, Penev said. "For the first time, we have evidence that the amount of sleep makes a big difference on the results of dietary interventions. One should not ignore the way they sleep when going on a diet. Obtaining adequate sleep may enhance the beneficial effects of a diet. Not getting enough sleep could defeat the desired effects."

The National Institutes of Health funded this study. Additional researchers include Dale Schoeller, PhD, of the University of Wisconsin, Madison, WI; plus Jennifer Kilkus, MS, and Jacqueline Imperial, RN, of the University of Chicago's General Clinical Resource Center; and Arlet Nedeltcheva, MD, at the University of Chicago at the time of the study but now at the U.S. Food and Drug Administration.

Most doctors are spending a good deal of time counseling their patients about diet and weight loss, but for the most part, it isn't making any difference, according to a new study appearing in the American Journal of Preventive Medicine.

Duke University Medical Center researchers recorded the conversations between 40 primary care physicians and 461 of their overweight or obese patients over an 18-month period. Investigators didn't tell them what they were listening for — only that they wanted to record the encounters to see how doctors talked about health. What they were really tracking, however, was how much time was spent and, specifically, how doctors talked with their patients about diet, exercise and weight loss.

Turns out, doctors talk about weight quite a bit. Physicians discussed weight with patients in 69 percent of the encounters.

"We found that on average, physicians spent about three and a half minutes talking about diet and weight loss," says Kathryn Pollak, PhD, a member of the Cancer Prevention Program in the Duke Comprehensive Cancer Center and the lead author of the study. "That may not sound like much, but it amounts to about 15 percent of the time of the average office visit, which ran about 20 minutes. So the good news is, physicians realize how important the issue is, and they are making a point to talk about it."

But the data showed that there was no difference in weight loss between those patients who received counseling and those who did not get it.

Investigators found a very different story, however, when they dug a little deeper and divided the doctors and their patients into groups according to communication styles.

They found that three months after the office visit, patients whose doctors talked about diet and weight loss in a more motivational fashion — using predominantly reflective or empathic statements — were much more likely to lose weight, compared to those whose physicians used a more judgmental or confrontational style of communication. Patients whose physicians communicated well lost about 3.5 pounds three months after the visit, which is substantial given most overweight and obese patients gain weight over time, says Pollak.

"Patients don't like to be told what to do, and they are generally not going to question or talk back to their doctor," says Pollak. "But what happens when doctors use reflective statements or a more motivational and empathic approach, it changes the relationship; the patient becomes more of an equal, more of a partner in care."

"So, for example, instead of asking a question like 'So, you can't fit exercise into your day?' a physician might say something like 'It sounds like you're finding it hard to find time to exercise.' That kind of reflection seems to help patients open up more and give more meaningful information to doctors."

Just over a third of the physicians in the study reported having some training in behavioral counseling, and Pollak says such instruction is becoming a higher priority item in traditional medical education.

She says the study is the largest of its kind and the first to examine not only the frequency of diet and weight counseling in physician office visits, but also the quality of the counseling and its impact on patients.

"Results of the study indicate that physicians may indeed have the power to help patients change their eating and exercise habits," says Pollak.

She says future research should examine whether weight loss that resulted from the sessions can be maintained over time, and whether improving physicians' training in behavioral communications would lead to more effective counseling and even greater weight loss.

The research was supported from grants from the National Cancer Institute and the Department of Veterans Affairs.

Duke colleagues who contributed to the study include Stewart Alexander, Cynthia Coffman, James Tulsky, Pauline Lyna, Rowena Dolor, Iguehi James, Rebecca Brouwer, Justin Manusov and Truls Ostbye.