Sunday, 14 June 2015
Why artificial sweetners make you eat more: your body can tell they provide no nutrients
How many people 'on a diet', eat foods labelled fat-free and low-calorie then find they are stuffing themselves with more food shortly after, and never lose weight?
One theory to explain this phenomenon is that artificial sweeteners don't contain the calories or energy that evolution has trained the brain to expect from sweet-tasting foods, so they don't fool the brain into satisfying hunger. However, until now, nobody understood how organisms distinguish between real sugar and artificial sweetener.
Now, a researcher at the University of Michigan has discovered how the brain of a fruit fly differentiates between the two. Because that molecular machinery is present in the guts and brains of humans on a larger scale, Monica Dus, assistant professor in the U-M Department of Molecular, Cellular, and Developmental Biology, believes human brains differentiate in the same way.
Fruit flies and humans share about 75% of the same disease-causing genes, says Dus, first author on a study that outlines the findings and appears in the journal Neuron.
"We can ask, 'Do these genes work the same in humans, to tell real sugar from artificial sweetener?'" Dus said. "The bits and pieces are there, so it is really possible that these genes work in a similar way. Plus, we knew that the human brain could tell the difference between real and fake sugar, we just did not know how."
Dus and colleagues Greg Suh and Jason Lai of New York University School of Medicine deprived fruit flies of food for several hours and then gave them a choice between diet, non-nutritive sweeteners and real sugar. When the flies licked the real sugar, it activated a group of six neurons that released a hormone with receptors in the gut and brain.
The hormone fueled digestion and allowed the fly to lick more of the nutritious food. On the other hand, when the fly licked the diet sweetener, it never produced this hormone/digestive reaction because zero-calorie sweetener has no nutritional or energy value.
In every case, the flies abandoned the artificial sweetener and chose the regular sugar because the starved flies needed the energy provided by the calories in the real sugar.
From an evolutionary perspective, sweet taste means sugar (traditionally from fruit or high concentrate carbohydrates) and a subsequent big energy boost. Fruit flies can't call out for pizza—their brains expect calories if they eat something sweet, and that's why they chose the regular sugar, Dus says.
If our brains work the same way, this helps explains why diet foods don't satiate or satisfy us, and we gain weight while dieting, she says. It's analogous to a person eating that entire sleeve of low-calorie cookies and the body telling her she's still hungry. She keeps snacking until she eats something with nutritional value that meets her energy needs.
The fruit fly has roughly 100,000 neurons and the human brain has about 86 billion. The six neurons identified in fruit flies are in roughly the same spot in humans, which removes an immense amount of guesswork and lets researchers zero in on a location. The neurons fire only when they encounter real sugar, which provides a very elegant way for the brain to differentiate between real sugar and artificial sweeteners since they taste similar.
In two previous studies, Dus and her colleagues found that flies that couldn't taste preferred real sugar to a zero-calorie sweetener, which underscores the theory of energy preference. They also characterized a neural circuit, dubbed Cupcake+, which functions as a behavioral on/off switch for eating. Turning off the Cupcake neurons makes the fruit flies "feel" hungry, Dus says.
Source: University of Michigan
Your health is affected by the month of your birth
Columbia University scientists have developed a computational method to investigate the relationship between birth month and disease risk. The researchers analysed New York City medical databases and found 55 diseases that correlated with the season of birth.
Overall, the study indicated people born in May had the lowest disease risk, and those born in October the highest. The study was published in the Journal of American Medical Informatics Association.
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| Credit: Dr Nick Tatonetti, Columbia University Medical Center. This data visualization maps the statistical relationship between birth month and disease incidence in the electronic records of 1.7 million New York City patients. |
"This data could help scientists uncover new disease risk factors," said study senior author Nicholas Tatonetti, PhD, an assistant professor of biomedical informatics at Columbia University Medical Center (CUMC) and Columbia's Data Science Institute. The researchers plan to replicate their study with data from several other locations in the U.S. and abroad to see how results vary with the change of seasons and environmental factors in those places. By identifying what's causing disease disparities by birth month, the researchers hope to figure out how they might close the gap.
Earlier research on individual diseases such as ADHD and asthma suggested a connection between birth season and incidence, but no large-scale studies had been undertaken. This motivated Columbia's scientists to compare 1,688 diseases against the birth dates and medical histories of 1.7 million patients treated at NewYork-Presbyterian Hospital/CUMC between 1985 and 2013.
The study ruled out more than 1,600 associations and confirmed 39 links previously reported in the medical literature. The researchers also uncovered 16 new associations, including nine types of heart disease, the leading cause of death in the United States. The researchers performed statistical tests to check that the 55 diseases for which they found associations did not arise by chance.
"It's important not to get overly nervous about these results because even though we found significant associations the overall disease risk is not that great," notes Dr. Tatonetti. "The risk related to birth month is relatively minor when compared to more influential variables like diet and exercise."
The new data are consistent with previous research on individual diseases. For example, the study authors found that asthma risk is greatest for July and October babies. An earlier Danish study on the disease found that the peak risk was in the months (May and August) when Denmark's sunlight levels are similar to New York's in the July and October period.
For ADHD, the Columbia data suggest that around one in 675 occurrences could relate to being born in New York in November. This result matches a Swedish study showing peak rates of ADHD in November babies.
The researchers also found a relationship between birth month and nine types of heart disease, with people born in March facing the highest risk for atrial fibrillation, congestive heart failure, and mitral valve disorder. One in 40 atrial fibrillation cases may relate to seasonal effects for a March birth. A previous study using Austrian and Danish patient records found that those born in months with higher heart disease rates--March through June--had shorter life spans.
"Faster computers and electronic health records are accelerating the pace of discovery," said the study's lead author, Mary Regina Boland, a graduate student at Columbia. "We are working to help doctors solve important clinical problems using this new wealth of data."
Source: Birth Month Affects Lifetime Disease Risk: A Phenome-Wide Method. The contributors are: Mary Regina Boland, Zachary Shahn, David Madigan, George Hripcsak, Nicholas P. Tatonetti (CUMC).
Journal link: http://jamia.oxfordjournals.org/content/early/2015/06/01/jamia.ocv046
Yoga, running, weight lifting, and gardening associated with better sleep habits
Physical activities, such as walking, as well as aerobics/calisthenics, biking, gardening, golfing, running, weight-lifting, and yoga/Pilates are associated with better sleep habits, compared to no activity, according to a new study from researchers at the Perelman School of Medicine at the University of Pennsylvania.
In contrast, the study shows that other types of physical activity – such as household and childcare — are associated with increased cases of poor sleep habits.
Physical activity is already well associated with healthy sleep, but the new study, led by Michael Grandner, PhD, instructor in Psychiatry and member of the Center for Sleep and Circadian Neurobiology at Penn, yields insight into whether specific types of physical activities may impact sleep quality.
Using data on sleep and physical activities of 429,110 adults from the 2013 Behavioral Risk Factor Surveillance System, the Penn researchers measured whether each of 10 types of activities was associated with typical amount of sleep, relative to both no activity and to walking. Survey respondents were asked what type of physical activity they spent the most time doing in the past month, and also asked how much sleep they got in a typical 24-hour period.
Since previous studies showed that people who get less than 7 hours are at greater risk for poor health and functioning, the study evaluated whether people who reported specific activities were more likely to also report sufficient sleep.
Compared to those who reported that they did not get physical activity in the past month, all types of activity except for household/childcare were associated with a lower likelihood of insufficient sleep. To assess whether these effects are just a result of any activity, results were compared to those who reported walking as their main source of activity.
Compared to just walking, aerobics/calisthenics, biking, gardening, golf, running, weight-lifting and yoga/Pilates were each associated with fewer cases of insufficient sleep, and household/childcare activity was associated with higher cases of insufficient sleep. These results were adjusted for age, sex, education level, and body mass index.
“Although previous research has shown that lack of exercise is associated with poor sleep, the results of this study were surprising,” said Grandner. “Not only does this study show that those who get exercise simply by walking are more likely to have better sleep habits, but these effects are even stronger for more purposeful activities, such as running and yoga, and even gardening and golf.
It was also interesting that people who receive most of their activity from housework and childcare were more likely to experience insufficient sleep —we know that home and work demands are some of the main reasons people lose sleep.”
“These results are consistent with the growing scientific literature on the role of sleep in human performance,” said Grandner. “Lab studies show that lack of sleep is associated with poor physical and mental performance, and this study shows us that this is consistent with real-world data as well. Since these results are correlational, more studies are needed to help us understand whether certain kinds of physical activity can actually improve or worsen sleep, and how sleep habits help or hurt a person’s ability to engage in specific types of activity.”
The full results of the study (Abstract #0246) were presented on June 8, at SLEEP 2015, the 29th annual meeting of the Associated Professional Sleep Societies LLC, June 6-10, in Seattle, WA.
Penn Medicine News from Sleep 2015 is available online at http://www.uphs.upenn.edu/news/.
How to keep hydrated while exercising in summer heat
Building a tolerance to heat
The ability to tolerate heat varies greatly between individuals. You can improve your capacity to withstand heat stress by repeated and slowly increasing exposures to heat over a period of ten days to two weeks. This process, called acclimatization, may take even longer in people who are less physically fit, children, elderly and those with chronic medical conditions or those using certain medications.
Keep hydrated
Dehydration, which results from the failure to replace fluids lost during activity, can increase the risk for exertional heat illness and stress the cardiovascular system. Experts recommend that to prevent dehydration and heat illness, water lost due to sweating should be replaced at a rate close to or equal to the amount of sweat lost.
For physically active adults, this can range from 3-10 liters per day.
It’s about more than thirst
Relying on thirst alone to determine fluid needs is inadequate. We experience the sensation of thirst only after our bodies are already experiencing the stress of fluid loss. In addition, drinking water extinguishes the sensation of thirst before restoration of fluid balance has occurred. Interspersing sports drinks, which contain sodium, with water during hydration actually helps maintain your thirst drive and may aid rehydration. Elderly, active individuals need to use more caution as their sense of thirst is diminished with dehydration.
“Under heat stress, children’s exercise tolerance time is reduced compared to adults,” says Dr. Roberta Millard, a sports medicine specialist at Penn State Hershey. “For that reason, children should be encouraged to drink more fluids than dictated by thirst alone.”
Individuals engaged in vigorous exercise or whose work involves sweating for two or more hours daily should especially take precautions in the heat. The appearance of urine can also be helpful to monitor fluid intake. If well-hydrated, your urine should have the appearance of lemonade. If your urine is dark and has the appearance of apple juice, you should drink more.
Drink up – and drink early
Hydration should begin prior to physical activity or work in the heat by drinking at least two cups of water or sports drink one to two hours prior to exercise. In hot weather, drinking between a half-cup and a whole cup of fluid for every 15 minutes of vigorous exercise is a general guideline. Drinking cool fluids does double duty, both hydrating and cooling of the body.
By knowing your limits, dressing appropriately and drinking the right things, you can stay safe during summertime exercise, and ensure the benefits you realize are not outweighed by heat-related illnesses that can take a toll on the body.
Source: Penn State Milton S. Hershey Medical Center
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